source string | id string | question string | options list | answer string | reasoning string |
|---|---|---|---|---|---|
SciQ | SciQ-2844 | electrostatics, charge
Title: Will charges attract or repel? If the universe consist of only two particles namely electron and proton, and if they are separated away by huge distance, they will still attract each other.
Can we prove it without using Coulomb's law?
Can we find out why they attract or what causes them to attract?
What really happens there that makes the both particles move towards each other? Physics does not answer why questions, except with how from postulates and mathematical models one can describe the data. The how is Coulombs law.
Physics is about fitting experimental observations with mathematical models. The answer to the "why attraction" in this case, is, data dictates so. There is no other answer except that Coulomb's law fits the data. Our present theories of physics incorporate this law in more inclusive mathematical models, because of this experimental fact.
The following is multiple choice question (with options) to answer.
Because opposite charges attract, oppositely charged ions attract each other to form what? | [
"ionic bonds",
"nuclear bonds",
"soluble bonds",
"particle bonds"
] | A | until all atoms have octets. Because some atoms will lose electrons and some atoms will gain electrons, there is no overall change in the number of electrons, but individual atoms acquire a nonzero electric charge. Those that lose electrons become positively charged, and those that gain electrons become negatively charged. Charged atoms are called ions. Because opposite charges attract (while like charges repel), these oppositely charged ions attract each other, forming ionic bonds. The resulting compounds are called ionic compounds and are the primary subject of this chapter. The second way for an atom to obtain an octet of electrons is by sharing electrons with another atom. These shared electrons simultaneously occupy the outermost shell of more than one atom. The bond made by electron sharing is called a covalent bond. Covalent bonding and covalent compounds will be discussed in Chapter 4 "Covalent Bonding and Simple Molecular Compounds". |
SciQ | SciQ-2845 | energy, fuel, environmental-chemistry
Title: Effect of coal and natural gas burning on particulate matter pollution I sometimes hear people talking about how we should replace coal burning plants with natural gas ones, to alleviate the case of particulate matter pollution. What exactly is the difference between coal fuel and natural gas that makes the latter seem "cleaner"?
At the same energy outcome, natural gas produces less carbon dioxide than coal. In a way, natural gas is half way between coal and hydrogen.
Coal produces smelly smoke, solid particles, sulfur dioxide and minor or trace heavy metal pollutants.
It is less known to common people, but power plants burning coal are more significant source of radioactive pollution than nuclear plants. This pollution is very diluted, but rather significant in absolute amount. Coal ash, used in past as a filler for some construction materials, has lead in some cases to significantly increased content of radium-226 in building walls. This radium is a product of long term decay of natural uranium. It further decays while producing radioactive gaseous radon-222, which is dangerous in long term inhalation because of lung cancer. As it stays in lungs as polonium-218 and its decay products.
See e.g. Uranium produced from coal ash
... the uranium concentration in the ash pile is about 150-180 parts per million, about 1/4th of the concentration often thought of as commercially viable for ISL[In Situ Leaching] mining. However, coal ash piles have some physical characteristics that might help overcome that disadvantage since they may be easier to drill and it might be easier to protect the local groundwater from contamination. ...
See Radon in building materials by Czech government agency for radiation protection.
The following is multiple choice question (with options) to answer.
A major source of primary pollutants is the burning of oil and coal, which are types of what? | [
"erosion fuels",
"renewable fuels",
"greenhouse gases",
"fossil fuels"
] | D | Outdoor air pollution is made of chemical particles. When smoke or other pollutants enter the air, the particles found in the pollution mix with the air. Air is polluted when it contains many large toxic particles. Outdoor air pollution changes the natural characteristics of the atmosphere. Primary pollutants are added directly to the atmosphere. Fires add primary pollutants to the air. Particles released from the fire directly enter the air and cause pollution ( Figure below ). Burning of fossil fuels such as oil and coal is a major source of primary pollutants ( Figure below ). |
SciQ | SciQ-2846 | biochemistry, botany
Title: Ripening bananas artificially: What is the biological theory behind? I am a resident of the tropical island of Sri Lanka, and we have a strange traditional method to ripen our banana harvest quickly.
What we do is this: We dig a pit in earth that is enough to put the whole banana cluster in. Then, after safely laying the bananas in the pit, we cover up the pit with a sheet such that only a small hole from a side remains: visualize a small 3-4 inch door to the pit.
After that, we light a fire with semi-dry leaves just outside the pit's door. (Semi-dry leaves are used to get as much smoke as possible. Dry leaves do not give that much smoke, because they completely oxidize quickly). And the smoke is sent through the door by blowing it with the aid of a bamboo.
This sends a good amount of smoke and warms the inside of the pit considerably. And by experience I can tell you that this makes the bananas to ripen really quickly. I have done a controlled experiment where half of the cluster was not put into the pit. Bananas in the pit ripen overnight and the control sample took days to ripen.
Can anybody explain what are the bio-mechanisms that are working here? Ripening of bananas (and other fruits) is induced by acetylene and ethylene (Ethyne and Ethene) (see reference 1), which acts as a hormone and induces the ripening process. The incomplete combustion of the leaves produces ethylene, additionally the warmth of the process will help the enzymes as well. There is even a paper about this technique (although it is unfortunately not accessible), see reference 2 for more information. Smoking Chambers are routinely used in this process, see reference 3 and 4.
References:
Role of Ethylene in Fruit Ripening
Effects of smoking on some physiological changes in bananas.
Fruit Ripening
Technology for ripening fruits as important as marketing them
The following is multiple choice question (with options) to answer.
What causes natural ripening in fruit? | [
"chloride",
"ethylene",
"acid",
"sulfur"
] | B | |
SciQ | SciQ-2847 | evolution, reproduction, natural-selection, sex, gamete
Title: Are there multicellular isogamous species? Are there multicellular isogamous species?
Seeking through the examples of wikipedia I would tend to think that there are no multicellular isogamous species.
Our knowledge about the sexual transmission of mitochondria and
plastids (hereafter organelles) in isogamous eukaryotes comes mostly
from studies of the yeast Saccharomyces cerevisiae and the green alga
Chlamydomonas reinhardtii which are both unicellular species. To
investigate organelle inheritance in a multicellular organism with
morphological isogamy, we studied the filamentous brown alga
Ectocarpus siliculosus, in which each gamete contributes one plastid
and at least one mitochondrion to the zygote. ...
2004 - Inheritance of organelles in artificial hybrids of the isogamous multicellular chromist alga Ectocarpus siliculosus (Phaeophyceae)
So it is possible, but it seems like very rare.
The following is multiple choice question (with options) to answer.
In species with sexual reproduction, each cell of the body has two copies of each what? | [
"cell",
"dna strand",
"rna strand",
"chromosome"
] | D | In species with sexual reproduction, each cell of the body has two copies of each chromosome. For example, human beings have 23 different chromosomes. Each body cell contains two of each chromosome, for a total of 46 chromosomes. You can see the 23 pairs of human chromosomes in Figure below . The number of different types of chromosomes is called the haploid number. In humans, the haploid number is 23. The number of chromosomes in normal body cells is called the diploid number. The diploid number is twice the haploid number. In humans, the diploid number is two times 23, or 46. |
SciQ | SciQ-2848 | ichthyology, vertebrates
Title: If an organism is supported only by cartilage, does it have an endoskeleton? Lamprey and sharks lack bones, but does this mean they are not classified as having an endoskelton? Does an organism need bone to be considered as having an endoskeleton? From wikipedia
An endoskeleton (From Greek ἔνδον, éndon = "within", "inner" + σκελετός, skeletos = "skeleton") is an internal support structure of an animal, composed of mineralized tissue.
Cartilage is a mineralized tissue so it counts as a skeleton from this definition. A bit further in the wikipedia article it says
The vertebrate endoskeleton is basically made up of two types of tissues (bone and cartilage)
The following is multiple choice question (with options) to answer.
On what part of bones would you expect to find cartilage? | [
"exterior",
"interior",
"end",
"marrow"
] | C | The adult human skeleton has 206 bones, some of which are named below ( Figure below ). Bones are made up of living tissue. They contain many different types of tissues. Cartilage, a dense connective tissue, is found at the end of bones and is made of tough protein fibers. Cartilage creates smooth surfaces for the movement of bones that are next to each other, like the bones of the knee. |
SciQ | SciQ-2849 | taxonomy, history
Title: How many species did Carl Linnaeus classify? How many species did Carl Linnaeus (senior) classify? More than 13,000.
Plants: >9,000 names.
In Systema Naturae 10th edition, commonly taken as the starting point of modern taxonomy, Linnaeus is reported to have published around 6,000 plant names (I haven't counted, but Müller-Wille gives 5,900 and Stearn says "almost 6,000". The Wikipedia figure of 7,700 may come from a different edition of Systema Naturae).
However, that's just SN10. Luckily, a wonderful source has compiled the names from all of Linnaeus's work:
The Linnaean Plant Name Typification Project of the Natural History Museum says that Linnaeus published more than 9,000 valid plant names in his life (names that are still valid under current nomenclatural conventions), and they have many of them in a searchable database with references to where Linnaeus published them.
Animals: >4,200 names.
For SN10, different authors give 4,236 or 4,378 animal names. Stearn says "nearly 4,400", so perhaps he too was unsure. The total number Linnaues described in his life is probably higher, as he did write separate zoological publications like Fauna Svevica, but I couldn't find a source like the project bringing together all of his animal names.
Müller-Wille S. 2006. Linnaeus' herbarium cabinet: a piece of furniture and its function. Endeavour 30: 60–64.
Stearn WT. 1959. The Background of Linnaeus's Contributions to the Nomenclature and Methods of Systematic Biology.)
The following is multiple choice question (with options) to answer.
Who invented the taxonomic classification system? | [
"gregor mendel",
"Pascal",
"Isaac Newton",
"carl linnaeus"
] | D | The Levels of Classification Taxonomy (which literally means “arrangement law”) is the science of naming and grouping species to construct an internationally shared classification system. The taxonomic classification system (also called the Linnaean system after its inventor, Carl Linnaeus, a Swedish naturalist) uses a hierarchical model. A hierarchical system has levels and each group at one of the levels includes groups at the next lowest level, so that at the lowest level each member belongs to a series of nested groups. An analogy is the nested series of directories on the main disk drive of a computer. For example, in the most inclusive grouping, scientists divide organisms into three domains: Bacteria, Archaea, and Eukarya. Within each domain is a second level called a kingdom. Each domain contains several kingdoms. Within kingdoms, the subsequent categories of increasing specificity are: phylum, class, order, family, genus, and species. As an example, the classification levels for the domestic dog are shown in Figure 12.3. The group at each level is called a taxon (plural: taxa). In other words, for the dog, Carnivora is the taxon at the order level, Canidae is the taxon at the family level, and so forth. Organisms also have a common name that people typically use, such as domestic dog, or wolf. Each taxon name is capitalized except for species, and the genus and species names are italicized. Scientists refer to an organism by its genus and species names together, commonly called a scientific name, or Latin name. This two-name system is called binomial nomenclature. The scientific name of the wolf is therefore Canis lupus. Recent study of the DNA of domestic. |
SciQ | SciQ-2850 | immunology, parasitology
Title: Why is untreated trypanosomiasis invariably fatal in humans? If left untreated, African trypanosomiasis will invariably kill the patient. The human immune system is unable to clear the infection.
I am aware of a few other infectious diseases with this property and I have a rudimentary understanding of the reason why. For example, I'm told that rabies has evolved to be uniquely good at attacking the brain because that's the only way it can spread to other hosts, and the neuroimmune system, being quite different from the peripheral immune system, is not capable of dealing with a virus that has this property.
I do not understand why the human immune system is ineffective against trypanosomiasis. One explanation I was offered is that the human immune system is just not very good at fighting parasitic infections (compared to viral and bacterial infections). However, this can't be the full answer, because there are other parasitic infections that may go away on their own without treatment. African trypanosomiasis, or sleeping sickness, is caused by the protozoan Trypanosoma brucei, a single-celled eukaryote. Being eukaryotic, it has a cell nucleus and a larger genome than most bacteria; it also has a flagellum with which it can propel itself. Infection with T. brucei occurs via the bite of a blood-sucking fly, one of several species of tsetse fly.
The mammalian immune system has a difficult time with T. brucei because of an effective set of adaptations. The protozoan's surface maintains a dense coat of a particular glycoprotein on its surface which generally hide other necessary surface features such as chemical receptors and ion channels. Since it is this glycoprotein that the adaptive immune system will encounter, that molecule is the one which it will develop antibodies to recognize.
The following is multiple choice question (with options) to answer.
What type of pathogen is responsible for african sleeping sickness? | [
"salmonella",
"Trichinella spiralis",
"streptococcus",
"trypanosoma"
] | D | Flagellates have long flagella, or tails. Flagella rotate in a propeller-like fashion, pushing the protist through its environment ( Figure below ). An example of a flagellate is Trypanosoma , which causes African sleeping sickness. |
SciQ | SciQ-2851 | soft-question, biophysics, biology
Title: Does physics explain why the laws and behaviors observed in biology are as they are? Does physics explain why the laws and behaviors observed in biology are as they are? I feel like biology and physics are completely separate and although physics determine what's possible in biology, we have no idea how physics determine every facets of biology. We know roughly how forces in physics may impact biological systems, but not every little connections and relations that exist between physics and biology. Am I wrong? To get more insight into a question like this, you might like to ponder the relationship between logic gates and programming languages in the case of computers. This is a lot simpler than the physics—biology question, but begins to open up some of the issues. When a computer runs a program, certainly lots of logic gates and memory elements etc. are enacting the process described by the program. But the logic gates do not themselves tell you much about the structure and nature of a high-level programming language such as Java or Python. In a similar way, further study of atoms and molecules will not in itself reveal much about the immune system in mammals, or the social structure of an ant colony, and things like that.
This "answer" is really a brief comment on what is, in the end, quite a deep issue concerning the whole nature and structure of scientific knowledge. Another useful thing to ponder is the relationship between the concepts involved when one moves from the equations of particle physics to many-body physics. There is every reason to consider that the motions of a non-linear many-body system are all consistent with the description offered by the Standard Model of particle physics for all the various fields and interactions. However, the low-level description does not in itself tell us how to formulate a field theory which correctly captures the main elements of the collective behaviour.
The following is multiple choice question (with options) to answer.
How many underlying principles does the science of biology have? | [
"four",
"five",
"eleven",
"three"
] | A | Four underlying principles form the basis of biology. They are cell theory, gene theory, homeostasis, and evolution. |
SciQ | SciQ-2852 | biochemistry, plant-physiology, plant-anatomy
Title: Why do plants store energy as carbohydrates and not as fats? In my introductory biology class, we are learning about biomolecules. The textbook says fats are a more efficient energy store than carbohydrates.
So my question is - why would plants store their energy as carbohydrates and not as fats, if fats are a more efficient energy store? There are quite some reasons for why plants prefer carbohydrates for energy storage rather than fats. I will reach some of them one at a time.
The following is multiple choice question (with options) to answer.
What are biochemical compounds, such as fats and oils, that consist of fatty acids and store energy? | [
"tissues",
"lipids",
"proteins",
"oils"
] | B | Lipids are biochemical compounds such as fats and oils. They consist of fatty acids, which may saturated or unsaturated. Lipids are used to store energy. They also make up cell membranes. |
SciQ | SciQ-2853 | quantum-mechanics, temperature, molecules, gas
Title: O2 molecues speed in air, and their limit Temperature is the proportional measure of kinetic energy of the random motion of the constituent micro particles in a system as per wikipedia.
Now I understand that O2 molecules are randomly moving in air at normal temperatures.
I could not find if we could define the speed of these molecules at a certain temperature.
Obviously these particles with rest mass cannot move as fast as light. So they must cause a max limit to temperature.
I wanted to know if there was a limit to the temperature of air (gases) due to this speed limit of their constituent gas molecules? Is this temperature the absolute max (like absolute min 0 K)? Have we ever seen anything close to this in the universe?
Question:
The following is multiple choice question (with options) to answer.
The temperature at which all molecular motion has ceased is called what? | [
"absolute zero",
"0 degrees celcius",
"stopping point",
"0 degrees kelvin"
] | A | Making Connections: Absolute Zero What is absolute zero? Absolute zero is the temperature at which all molecular motion has ceased. The concept of absolute zero arises from the behavior of gases. Figure 13.9 shows how the pressure of gases at a constant volume decreases as temperature decreases. Various scientists have noted that the pressures of gases extrapolate to zero at the same temperature, –273.15ºC . This extrapolation implies that there is a lowest temperature. This temperature is called absolute zero. Today we know that most gases first liquefy and then freeze, and it is not actually possible to reach absolute zero. The numerical value of absolute zero temperature is –273.15ºC or 0 K. |
SciQ | SciQ-2854 | terminology, metabolism, energy-metabolism
As Wikipedia puts it (emphasis mine):
An endotherm is an organism that maintains its body at a metabolically favorable temperature, largely by the use of heat released by its internal bodily functions instead of relying almost purely on ambient heat.
That really does seem to better match the "exo-" prefix.
Is there a real inconsistency here, or do I just understand this incorrectly? The prefix "endo" comes from the Greek "endon" meaning "inner". "Therm" comes likewise from the Greek "therme" meaning heat.
Thus Endo = inner, Therm = heat, heat from inside!
The confusion applies in chemistry, not in that someone has it wrong, but that molecular reactions sometimes release heat - this is obviously to the outside so it must be "exo". The Greek opposite of exo is endo, so the converse reaction (absorbing heat) must be endothermic.
Note also that in the case of an endothermic reaction, the heat supplied for the reaction to work comes from within the materials of the reaction, it's just that in the process of the reaction occurring the heat is "used up" so the reaction vessel feels cold. Because the heat is coming from inside the reaction "endo" makes sense here too.
I did my basic chemistry too long ago for me to remember for endothermic reactions if environmental heat is needed for the reaction to proceed, but I suspect that at any temp above 0 K, the answer is generally no; the heat comes from breaking of intra-molecular bonds.
The following is multiple choice question (with options) to answer.
What term means controlling body temperature within a narrow range from the inside through biochemical or physical means? | [
"regulation",
"endothermy",
"evaporation",
"exothermy"
] | B | Both mammals and birds evolved endothermy. Endothermy means controlling body temperature within a narrow range from the inside through biochemical or physical means. For example, on a cold day, an endotherm may produce more body heat by increasing its rate of metabolism. On a hot day, it may give off more heat by increasing blood flow to the surface of the body. That way, some of the heat can radiate into the air from the body’s surface. Endothermy requires more energy (and food) than ectothermy. However, it allows the animal to stay active regardless of the temperature outside. You can learn more about how vertebrates regulate their temperature by watching this video: https://www. youtube. com/watch?v=TSUCdLkI474 . |
SciQ | SciQ-2855 | physiology, herpetology, poison, amphibians
+
0.002 mg/L will fatally damage the sensitive skin on tadpoles, frogs, salamanders and other amphibians.
another source:
Free chlorine (Cl2) is a greenish gas that is well known for its
highly toxic properties as can be attested to by the thousands of
soldiers that died and were severely injured from chlorine exposure
during World War I. In water, chlorine is the most toxic substance
that we will discuss. Ironically for the amphibian keeper, it is this
toxic nature of chlorine and its ability to denature proteins, which
makes its encounter inevitable. Chlorine is generally used as an
antibacterial agent in municipal water supplies and may be present in
concentrations of over 9 mg/1 in some tap water (measured in Houston,
Texas as an example, although levels were generally lower). The
concentration of chlorine in municipal water supplies can vary greatly
from day to day, or even hour to hour, depending on conditions at the
water treatment facilities. Concentrations as low as 0.0034 mg/1 have
been noted to reduce reproduction in fathead minnows with 72 hour
LC100 (lethal concentration for 100% kill) at 0.15 mg/1 (Arthur and
Eaton,1971). LC50 (96 hour) for the shiners (Notemigonus chrysoleucas)
was as low as 0.19 mg/1 (Esvelt et al., 1971). The concentrations
found in municipal water supplies are many times greater than the
minimum lethal concentrations for many aquatic life forms.
Thus, the well being of the frog in the water of the swimming pool depends on the time the frog spends in the water. Eventually, with extended exposure the chlorine concentration will exceed the one compatible will life and the frog will die. This time is multifactorial variable, thus cannot be assessed easily - the weight and the skin surface area and skin permeability will affect the frog survival in a great degree.
The following is multiple choice question (with options) to answer.
The most important characteristic of extant amphibians is a moist, permeable skin used for this? | [
"cutaneous respiration",
"avian respiration",
"benign respiration",
"simple respiration"
] | A | 29.3 Amphibians As tetrapods, most amphibians are characterized by four well-developed limbs, although some species of salamanders and all caecilians are limbless. The most important characteristic of extant amphibians is a moist, permeable skin used for cutaneous respiration. The fossil record provides evidence of amphibian species, now extinct, that arose over 400 million years ago as the first tetrapods. Amphibia can be divided into three clades: salamanders (Urodela), frogs (Anura), and caecilians (Apoda). The life cycle of frogs, like the majority of amphibians, consists of two distinct stages: the larval stage and metamorphosis to an adult stage. Some species in all orders bypass a free-living larval stage. |
SciQ | SciQ-2856 | genetics, cell-biology, embryology, meiosis, gamete
Title: Fertilization of the human egg- where does our centrosome come from? Is there a centrosome in a human egg cell? Is the reason why the egg cell remains paused before meiosis 2 because there isn't a centrosome, and it only divides when the sperm fertilizes it thus it can have a centrosome? If this is so, then how did oogenesis happen? ? To answer the first part of your question. The sperm actually introduces two centrosomes. The centrosome then nucleates the new microtubule assembly to form the sperm aster — a step essential for successful fertilization. You can visit these sites Simerly, et al as well as Paweltz, et al
The following is multiple choice question (with options) to answer.
Fertilized mollusk eggs develop into what? | [
"bark",
"shrimp",
"leaf",
"larvae"
] | D | Mollusks reproduce sexually. Most species have separate male and female sexes. Fertilization may be internal or external, depending on the species. Fertilized eggs develop into larvae. There may be one or more larval stages. Each one is different from the adult stage. |
SciQ | SciQ-2857 | biochemistry, metabolism, enzymes, human-physiology, fat-metabolism
[My de-emphasis of glycolysis]
To understand this requires one to consider the different functions of liver and adipose tissue and how they should respond to the fed and fasted state. Then one can appreciate that the differences in enzyme complement are one of the ways by which this is achieved. (The other is their differential responses to hormones.)
The role of the adipose tissue is to store fat (triglycerides) in the fed state and make it available for the other tissues in the body in the fasted state.
The role of the liver is to divert metabolism to the synthesis of fat in the fed state (at the appropriate stage) and to ensure that there is a supply of glucose in the fasted state for those tissues that depend on it (brain, erythrocytes) or a supply of ketone bodies for the brain.
The substrates for triglyceride synthesis are L-glycerol phosphate and fatty acids. There are two enzymes that can catalyse its production, glycerokinase (glycerol kinase) in the liver and glycerol 3-phosphate dehydrogenase in both liver and adipose tissue, as shown in my diagram below:
Fed State
The liver has surplus glucose so it can switch to fatty acid production from acetyl CoA (from pyruvate) and generate L-glycerol phosphate from the dihydroxyacetone phosphate intermediate of glycolysis, catalysed by glycerol 3-P dehydrogenase. This allows the synthesis of triglyceride, which is exported as lipoprotein.
When the triglyceride reaches the adipose tissue it is broken down to fatty acids and glycerol by the hormone-sensitive lipase. The glycerol cannot be used by the adipose tissue, but adipose tissue can synthesize L-glycerol phosphate itself in the same way as liver as there is glucose available for glycolysis in the adipose tissue. Hence the triglyceride can be resynthesized and stored.
Fasted State
The following is multiple choice question (with options) to answer.
Proper kidney function is essential for homeostasis of what level, which in turn helps ensure the functioning of enzymes? | [
"ions",
"oxygen",
"calcium",
"ph"
] | D | pH Regulation Recall that enzymes lose their three-dimensional conformation and, therefore, their function if the pH is too acidic or basic. This loss of conformation may be a consequence of the breaking of hydrogen bonds. Move the pH away from the optimum for a specific enzyme and you may severely hamper its function throughout the body, including hormone binding, central nervous system signaling, or myocardial contraction. Proper kidney function is essential for pH homeostasis. |
SciQ | SciQ-2858 | proteins, amino-acids, classification
Title: Classifying Polypeptides (and/or Proteins) Since polypeptides are a linear chain of twenty amino acids, each having a single letter abbreviation (e.g. Alanine = A). So can a polypeptide be represented as just the sequence (say: ADN for an Alanine, Aspartic acid, Asparagine polypeptide)?
This method of classifying polypeptides would lead to a possible 8000 (20**3) variations just for 3-amino-acid-polypetides (3200000 for 5-amino-acid-polypeptides, etc.) and that there would be many variations; and for longer polypeptides - that is, proteins - there would be even more variations.
Or are only the important polypeptides and proteins named, since not every variation of polypeptides and proteins are found in the body? I would've thought that many proteins (and enzymes, etc.) are incredibly specific and so they could be classified in some methodological way, as opposed to just 'lipase' or 'carbohydrase' which provides no structural information (though it would have a long methodological name). You can certainly refer to short peptides by their sequence. I don't know of any exact boundaries, but I've seen tripeptides referred to by either their three letter codes (Ala-Asp-Asn) or even the chemical name (alanylaspartylasparagine) although obviously that gets ridiculous pretty quickly.
As the largest known protein, titin also has the longest IUPAC name of
a protein. The full chemical name of the human canonical form of
titin, which starts methionyl... and ends ...isoleucine, contains
189,819 letters and is sometimes stated to be the longest word in the
English language, or any language. However, lexicographers regard generic names of chemical compounds as verbal formulae rather than English words
The following is multiple choice question (with options) to answer.
Proteins include 20 common types of what compounds? | [
"mitochondria",
"rna acids",
"dna",
"amino acids"
] | D | There are 20 common amino acids in proteins. There are 64 possible codons, more than enough to code for the 20 amino acids. The genetic code is shown in Figure below . To see how scientists cracked the genetic code, go to this link: http://www. dnalc. org/view/16494-Animation-22-DNA-words-are-three-letters-long-. html . |
SciQ | SciQ-2859 | nuclear-physics
Title: Why are elements with even atomic number more abundant? In reading this article about the origins of elements, I found the following diagram:
What strikes me about this image is the very consistent zig-zagging of the line that appears to indicate that elements/isotopes with an even number are more abundant.
Am I correct? What's going on here? I will add to the answer from @BowlofRed https://physics.stackexchange.com/a/158270/36194 that the nuclear pairing interaction lowers the energy in nuclei where the number of like nucleons is even: thus for instance there are more isotopes with even rather than odd number of neutrons. This also favors the formation of even-proton-numbered nuclei over the neighbouring odd ones.
The following is multiple choice question (with options) to answer.
Isotopes have different number of these in their nuclei? | [
"protons",
"electrons",
"atoms",
"neutrons"
] | D | Isotopes have different numbers of neutrons in their nuclei. |
SciQ | SciQ-2860 | cancer, mutations
Here is another great paper that specifically addresses your question, linking increased cell division with the accumulation of both significant and insignificant mutations, which over time, lead to an accumulation of mutations needed for cancer to develop.
The following is multiple choice question (with options) to answer.
What can destroy living cells, produce mutations and cause cancer? | [
"plasma rays",
"prismatic rays",
"stingrays",
"gamma rays"
] | D | Gamma rays can destroy living cells, produce mutations, and cause cancer. They can be used to treat cancer by focusing the deadly rays on cancer cells. |
SciQ | SciQ-2861 | taxonomy
Title: Why are sponges sometimes not considered multicellular? I read somewhere (I can't find where) that there is no scientific consensus whether sponges should be considered multicellular organisms.
It seems I don't understand where is the line between unicellular and multicellular life.
I am not able to find a more elaborate explanation of that doubt. What are the reasons for it? Sponges are generally considered as colonial organisms because there is little cell specialization and little separation of function/role. All cells do pretty much the same thing; it looks more like a pile of individual cells than an actual multicellular organism. In reality it is a little bit in between.
In any case, what one wants to call multicellular or unicellular is a matter of definition and preferences. You cannot find the line between unicellular and multicellular because there is no such line that would not be very arbitrary and filled with special cases.
You can study a little more the physiology of sponges and then decide for yourself if it looks sufficiently like a multicellular organism or more like a colony of cells (a colonial organism).
The following is multiple choice question (with options) to answer.
What type of feeders are sponges? | [
"layer feeders",
"bottom feeders",
"filter feeders",
"surface feeders"
] | C | Other specialized cells are involved in feeding. Sponges are filter feeders. They filter food out of the water as it flows through them. Sponges pump water into their body through specialized pore cells called porocytes. |
SciQ | SciQ-2862 | human-physiology, digestion, stomach
The stomach accomplishes much of its function by mechanically breaking down the swallowed food particles and mixing them with acid and enzymes into a sort of slurry. To do this, there are three major layers of muscle surround the stomach - from the outside, the longitudinal layer, the circular layer, and the oblique layer. The stomach also has two holes in it - the gastroesophageal opening, coming from the esophagus with the swallowed food/saliva mix, and the pylorus, where the food/acid/enzyme slurry exits into the duodenum, which is the beginning of the small intestine.
Due to the three layers of (rather strong) muscle, the stomach doesn't have a lot of expansion capability once it is filled completely to capacity. Fortunately, this almost never occurs (despite how we may feel after a large meal) because material is always leaving the stomach on its way to enzymatic digestion in the intestines. Additionally, once the stomach is filled to a certain extent, hormones such as leptin are secreted that give you the feeling of being sated, or full, triggering the brain to make you stop eating.
Of course, as we can see with the current epidemic of obesity around the world, the stomach can change its size over time. However, this is a rather slow process (weeks to months to years) of adapting to continuously consuming large meals.
But what would happen if you completely ignored these internal warnings, or were being force-fed, or whatever? Instead of rupturing (the biological equivalent of "exploding"), food would most likely be expelled either into the small intestine or back into the esophagus and back up the way it came down, i.e. causing vomiting.
The following is multiple choice question (with options) to answer.
The first consumption of breast milk or formula floods the baby's gastrointestinal tract with what? | [
"hemoglobin",
"nerves",
"beneficial bacteria",
"enzymes"
] | C | Gastrointestinal and Urinary Adjustments In adults, the gastrointestinal tract harbors bacterial flora—trillions of bacteria that aid in digestion, produce vitamins, and protect from the invasion or replication of pathogens. In stark contrast, the fetal intestine is sterile. The first consumption of breast milk or formula floods the neonatal gastrointestinal tract with beneficial bacteria that begin to establish the bacterial flora. The fetal kidneys filter blood and produce urine, but the neonatal kidneys are still immature and inefficient at concentrating urine. Therefore, newborns produce very dilute urine, making it particularly important for infants to obtain sufficient fluids from breast milk or formula. |
SciQ | SciQ-2863 | mass, weight
Title: Mass versus Weight What are the difference between mass and weight? I keep getting confused in my physics class, and I am in 8th grade. Thank you in advance. Mass is a measure of how much matter (atoms) make up an object. Weight is a force that results from that quantity of matter accelerating in a gravitational field. Weight = mass*acceleration due to gravity. Weight can change depending on what gravitational field you are in, mass cannot change.
The following is multiple choice question (with options) to answer.
Weight refers to what force acting on a mass? | [
"gravitational",
"magnetic",
"solar",
"electronic"
] | A | The terms mass and weight, while often used interchangeably, are technically different terms. Mass is the quantity of inertia possessed by an object. Weight refers to the gravitational force acting on a mass, as measured on a scale. On the surface of the earth, the numerical values of mass and the corresponding force of gravity (weight) are approximately equivalent. For now, we will use the terms mass and weight interchangeably although mass is the more appropriate scientific term. |
SciQ | SciQ-2864 | human-biology, biophysics, skin, light, uv
Title: Can UV radiation be safe for the skin? It is well known that UV radiation can damage the DNA and generally harm our skin.
We also know that UV radiation helps on the production of melanin and Vitamin D.
From what I could find, the DNA absorption spectrum goes to almost zero for wavelengths higher than 300 nm. This seems to suggest that we would be safe to use UV radiation between 300 and 340 nm in our skin (as long as the power or exposure is not too high/long to make burns), for therapeutic purposes such as the stimulation of Vitamin D production.
Is this assumption correct? Are there any evidences that we could use this UV wavelength range safely? You're talking about long-wave UV, or UV-A radiation. In the 80s, experts claimed that this was a safe wavelength. Protection against UV-A was not part of sunscreen in the early days. Consequently, UV-A was (and still is) used in tanning beds due to its perceived safety over UV-B. However, a lot of research has been done since.
UV-A is well understood now to also be unsafe in unreasonable amounts. Currently, UV-A protection is a typical feature of sunscreen and tanning beds are still not a healthy alternative to moderate, healthy doses of sun. Here is a recent review covering some of the aspects comparing different UV range effects on skin. I really suggest you put a search engine to good use here; it makes little sense for us to expound on the literature when it is so clear and easily available.
In summary,
UVA certainly contributes to the development of skin cancer.
UVA penetrates deeper into the skin than UV-B (which is largely responsible for 'burning' of the topmost layer of skin, without directly affecting the deeper layers). For this reason, UV-B is associated primarily with burning and UV-A is primarily associated with aging and aging diseases like cancer.
It is important to note that 95% of UV light in every day life is UV-A, because it does not vary seasonally and can penetrate clouds and windows. Therefore, in spite of the fact that short wavelengths carry more energy per photon, the ratios of UV-A and UV-B exposure are far from equal.
These are only a few of the explanations as to why we observe an incidence of aging and skin damage and disease upon UV-A exposure.
The following is multiple choice question (with options) to answer.
Being exposed to sunlight will produce what vitamin in the skin? | [
"vitamin A",
"vitamin d",
"Vitamin E",
"B-complex"
] | B | Some vitamins are produced in the body. For example, vitamin D is made in the skin when it is exposed to sunlight. Vitamins B 12 and K are produced by bacteria that normally live inside the body. Most other vitamins must come from foods. Foods that are good sources of vitamins include whole grains, vegetables, fruits, and milk ( Table above ). |
SciQ | SciQ-2865 | evolution, human-evolution
Title: Can there be significant new changes in physical features of Humans due to evolution in 10000 years of span? Humans migrated from Africa about 60000 years. And in these years humans physical features undergone significantly in terms of skin color, hair, eye color and facial features.
So, with this we can say that given 10000 years of span we can see a significant noticeable new changes in physical features of humans? like some humans with new skin color (apart from today's white, black and brown), new color eye balls, big heads etc.? Yes & perhaps (or probably?) no, depending on what you define as significant changes.
Less than 10,000 years ago everyone in the british isles & the rest of europe were dark skinned so the answer if (unlike me) you consider the change in skin color a significant change is obviously a resounding yes.
Here's what English people looked like 10,000 years ago
Darker skinned than you were expecting perhaps.
If as suggested in this article white skin arrived in Europe around 5,000 years ago that only leaves 2,000 years before early Greek & Roman art we have available which shows it as ubiquitous, so it perhaps took only 2,000 years or so (maybe less) to become dominant in europe, that's fast.
Using 20 years as the measure of a generation that's only 100 generations, so, very fast.
Timeline of human prehistory
The first reconstruction in the link below is a reconstruction of a Neanderthal woman found in a cave in Gibraltar. She died at least 30,000 years ago.
Here she is, the skin tone may not be accurate but we do know from gene's recovered from Neanderthal remains that they were relatively light skinned.
Personally I don't consider her appearance to be significantly different from modern humans.
29 Reconstructed Faces Of Ancient People
So my answer based on what I consider significant changes would be no.
But for you or others the answer may well be yes.
And of course a mutation for a new eye colour could appear at any time in one individual & spread like wildfire practically overnight just because we think it's unusual & 'cool' (aka sexual selection) so if eye color ticks your boxes it's a very definite yes.
The following is multiple choice question (with options) to answer.
Modern plants reflect what kind of changes that have occurred over many, many years? | [
"tissue changes",
"tendency changes",
"unknown changes",
"evolutionary changes"
] | D | The types of living plants today reflect the evolutionary past of the plant kingdom. From tiny nonvascular mosses to large flowering and fruiting trees, there are modern plants that represent each of the major evolutionary changes that occurred in this important eukaryotic kingdom. |
SciQ | SciQ-2866 | electromagnetism, electric-current, torque
Title: How does galvanometer measure more current than is passing through it? My textbook clearly states:
after putting a shunt in parallel to it, a galvanometer becomes an ammeter.
The diagram is quite similar to this:
source
This is fine. I have problem with this:
Now the same acale of the galvanometer which was recording the maximum current $I_g$ before conversion into ammeter will record maximum current I after conversion into ammeter. It means each division of scale in ammeter will be showing higher current than that of galvanometer.
I don't understand how can galvanometer measure current which is not even passing through it? I know we can calculate I from Ig as:
$I_g = I \times S \div (G+S)$
So if we know Ig (which galvanometer is measuring) we can find I. But how does that mean that galvanometer's scale changes and it starts measuring the current which is not even paasing through it? Galvanometer still shows maximum deflection when maximum current is passing through it. But out of the total current in the circuit only some of it goes towards galvanometer and rest goes to shunt. So the actual current in the circuit is more than which is passing through galvanometer.
But the galvanometer is calibrated accordingly that it will show the reading of $I$ and not $I_g$.
Galvanometer still shows deflection proportional to $I_g$ but the reading is different as the calibration is different. Hence the reading is I though current in galvanometer though the current through it is Ig because the 1 divisions or marking on ammeter is actually different than what actual current is passing through it.
So though $I_g$ is current it shows $I_g+I_s$ as it is calibrated as such.
So suppose there are 10 divisions then Ig is maximum current so when Ig/10 current passes it shows deflection of one division but the galvanometer is calibrated as 1 division =I/10. That maximum current measured by ammeter is I.
The following is multiple choice question (with options) to answer.
What device measures current that flows through wire? | [
"resistor attachment",
"Geiger counter",
"ammeter",
"protractor"
] | C | The device in the circuit in Figure above is an ammeter. It measures the current that flows through the wire. The faster the magnet or coil moves, the greater the amount of current that is produced. If more turns were added to the coil, this would increase the strength of the magnetic field as well. If the magnet were moved back and forth repeatedly, the current would keep changing direction. In other words, alternating current would be produced. This is illustrated in Figure below . |
SciQ | SciQ-2867 | vectors
Title: Definition of Position Vectors I have a few (possibly very stupid) questions relating to position vectors; more specifically my confusion about them.
Following Halliday and Resnick's text, we define vectors by their magnitude and direction, but not by their 'location' in space. They give as an example the displacement vector, and draw three of the same vector in different locations to emphasize that shifting the vector does not change it.
Then in the next chapter we are introduced to position vectors relative to a given origin, which is a vector extending from the origin to the position of the particle.
How are we to think about position vectors? It seems like location is also important, even though we only defined vectors as having magnitude and direction.
How do we think about the addition of a displacement to a position vector? We define displacement vectors as the difference between two position vectors. Mathematically this is the same as saying that the final position vector is the result of adding the displacement vector to the initial position vector. The vector algebra doesn't care which ones are assigned the label of 'position' or 'displacement'; do we simply agree that when we add a 'displacement' vector to a 'position' vector, we get a 'position' vector?
Thanks This is one of those things that (intentionally) gets conflated, though it may be better if we were more consistent about keeping them separate.
So, points don't form a vector space. It makes no sense to ask "what's the location of New York plus the location of DC". However, given two points we can subtract them and get a displacement, and we can add that displacement to points to get new points. The mathematical structure for this is called (among other things) a torsor.
Your text is, however, accurate. If we choose a particular point to be our origin, call it $O$, then we can make a vector $r = P - O$ and call it a position vector for $P$. Now the difference between a position vector and a "regular" vector is that it changes when we change what we consider the origin. When we perform a translation on a system, position vectors change, regular vectors do not.
The following is multiple choice question (with options) to answer.
In science, what is defined as a change in position? | [
"speed",
"gravity",
"motion",
"direction"
] | C | In science, motion is defined as a change in position. An object’s position is its location. Besides the wings of the hummingbird in the opening image, you can see other examples of motion in the Figure below . In each case, the position of something is changing. |
SciQ | SciQ-2868 | ichthyology, vertebrates
Title: If an organism is supported only by cartilage, does it have an endoskeleton? Lamprey and sharks lack bones, but does this mean they are not classified as having an endoskelton? Does an organism need bone to be considered as having an endoskeleton? From wikipedia
An endoskeleton (From Greek ἔνδον, éndon = "within", "inner" + σκελετός, skeletos = "skeleton") is an internal support structure of an animal, composed of mineralized tissue.
Cartilage is a mineralized tissue so it counts as a skeleton from this definition. A bit further in the wikipedia article it says
The vertebrate endoskeleton is basically made up of two types of tissues (bone and cartilage)
The following is multiple choice question (with options) to answer.
What makes up the core of the endoskeleton? | [
"notochord",
"thorax",
"vertebral column",
"dermis"
] | C | The main distinguishing feature of vertebrates is their vertebral column, or backbone (see Figure below ). The backbone runs from the head to the tail along the dorsal (top) side of the body. The vertebral column is the core of the endoskeleton. It allows a vertebrate to hold its shape. It also houses and protects the spinal (nerve) cord that passes through it. The vertebral column is made up of repeating units called vertebrae (singular, vertebra). In many species, there are shock-absorbing discs between the vertebrae to cushion them during movement. |
SciQ | SciQ-2869 | oceanography, rivers, satellite-oddities
Title: What are these river/canyon-like carvings in the ocean? Browsing around Google Maps, I came across this off the south-west coast of Ireland
It looks very consistent with the shape rivers and their tributaries might make, but it has me puzzled since it's all underwater!
The main, most "river-like" one is in the middle-left of the picture but there are more (which look more like fjords) at the bottom.
What caused this feature? The carvings are submarine canyons, a part of the continental slope leading from the continental shelf to the continental rise and ultimately the Abyssal plains. They are a product of :
erosion through currents and
slumping of the continental shelf
Like other erosive or slumping effects, they can be self-reinforcing, leading to canyon-like structures. The highlighted canyon here is the Gollum Channel system, seen here.
The following is multiple choice question (with options) to answer.
The bottom of the ocean is called what? | [
"Final zone",
"the benthic zone",
"Intertidal zone",
"Demersal zone"
] | B | The bottom of the ocean is called the benthic zone. It includes the sediments on the bottom of the ocean and the water just above it. Organisms living in this zone include clams and crabs. They may be few in number due to relatively scarce nutrients in this zone. |
SciQ | SciQ-2870 | core, mantle, drilling
Title: Can we really travel through earth's core? Inspired by the movie, "The Core".
Can we really travel through earth's core? I will provide 2 sub questions:
Is there any substance that can resist the heat of earth's core?
Between the crust and mantle, and the mantle and outer core is there any "wall" between them? And how hard is the wall (can we go through it)? As Chris Mueller said, in short: it isn't, or at least highly infeasible. Projects to drill into the mantle, such as the Kola Superdeep Borehole, have all failed because drilling equipment can't withstand the heat at only ~15km deep. Even if we were to come up with some sort of cooling system that's able to cool to 6400km or 12800km deep (depending on whether you would drill from one side only or from both sides at the same time), pressure is the second barrier that holds us from traveling through the earth's core.
According to Lide (2006) the pressure in the inner core is 330 to 360 GPa, at which iron becomes a solid even at the high temperatures in the core. If you could drill as far as the core you would have to build a device that's able to withstand that pressure, because if you can't, the material surrounding your well would immediately become liquid and fill the hole, if not shoot up your well towards the surface.
There are no physical walls between the layers of the Earth, only transition zones where temperature and pressure combinations lead to different behaviour of the materials. An example is the Mohorovičić discontinuity, or Moho, which is the boundary between crust and mantle, below which temperatures are high enough and at the same time the pressure is low enough so that rock becomes either liquid or at least a "flowing" solid. Similarly, at the boundary between the inner and outer core the pressure is so high that even at those temperatures the iron becomes a solid.
Lide, D.R., ed. (2006-2007). CRC Handbook of Chemistry and Physics (87th ed.). pp. j14–13.
The following is multiple choice question (with options) to answer.
Made of hot, solid rock, the mantle is beneath what layer of the earth? | [
"core",
"crust",
"volcanic",
"liquid"
] | B | Beneath the crust is the mantle . The mantle is made of hot, solid rock. They know this because of seismic waves, meteorites, and the heat that comes from inside the planet. Mantle rock is mostly peridotite , which is rich in iron and magnesium ( Figure below ). Peridotite is rare at Earth's surface. |
SciQ | SciQ-2871 | thermodynamics, heat, ideal-gas
Title: Combined gas law in an open atmosphere The question was asked about pressure vs. Volume increasing in an ideal gas as temperature is increased. My question then is this. What is the formula to determine how much volume and pressure will increase as temperature is increased?
Let me frame the question this way. PV/T=P2V2/T2 this formula works for a controlled system where more than one of these values can be maintained. If we apply a known amount of heat, say n, to the atmosphere, what formula would be used to calculate volume and pressure as the temperature is increased? Technically speaking, If you managed to create a planet with an ideal gas atmosphere, the atmosphere would just float away. Why?
One of the approximations of an ideal gas is
There are no attractive or repulsive forces between the molecules or the surroundings
This means that the gas wouldn't feel the force of gravity!
So if I had a jar of ideal gas, the pressure wouldn't increase as I went to a greater depth in the jar(It does increase in gasses too, just like it does in liquids).
I know this sounds strange but all it really means is that you cannot apply the ideal gas approximation to a system the size of our atmosphere. This approximation works well for small systems(A jar of ideal gas), because the effects of gravity are pretty negligible.
So to analyse effects of change in temperature on the whole atmosphere, you'll need a better model. Maybe considering the atmosphere a non-viscous fluid can help, I don't know. You should research on this.
Note that other approximations like the Van der Waals equation wouldn't help too because they too neglect the effect of gravity.
The following is multiple choice question (with options) to answer.
What happens to the volume of the gas when temperature increases but amount of gas and its pressure are constant? | [
"volume decreases",
"volume remains constant",
"nothing",
"volume increases"
] | D | There are other measurable characteristics of a gas. One of them is temperature (T). Perhaps one can vary the temperature of a gas sample and note what effect it has on the other properties of the gas. Early scientists did just this, discovering that if the amount of a gas and its pressure are kept constant, then changing the temperature changes the volume (V). As temperature increases, volume increases; as temperature decreases, volume decreases. We say that these two characteristics are directly related. A mathematical relationship between V and T should be possible except for one thought: what temperature scale should we use? We know from Chapter 2 "Measurements" that science uses several possible temperature scales. Experiments show that the volume of a gas is related to its absolute temperature in Kelvin, not its temperature in degrees Celsius. If the temperature of a gas is expressed in kelvins, then experiments show that the ratio of volume to temperature is a constant:. |
SciQ | SciQ-2872 | cell-biology, meiosis, mitosis
Title: Is the cell cycle applicable to meiosis as well, or just mitosis? All the diagrams I can find, show the cell cycle as having G1 phase (growth 1), S phase (DNA replication), G2 (growth 2) before the Mitotic phase (mitosis + cytokinesis).
Is there an equivalent "cell cycle" for meiosis, since the chromosomes in parent cell in meiosis also having "double" the genetic material prior to cell division (presumably from DNA replication too)?
Is it simply the same cell cycle as mitosis but with a Meiotic phase instead of Mitotic?
If so, would appreciate if anyone had a diagram :) Thanks! The cell cycle is only associated with mitosis. The cell cycle is the normal process of cell division with which cells can indefinitely increase their number by cyclically repeating the process. When a cell goes through the cycle, the result is two cells that are genetically identical.
Meiosis is a special type of cell division (which can occur only in eukaryotes) that produces cells that are not genetically identical to the initiating cell. The number of chromosomes in each of the resulting cells is half the number that were in the initial cell. (These haploid cells can later participate in fertilization, producing a cell with the original number of chromosomes.) Many of the steps of meiosis are similar to the steps involved in mitosis, but overall the process is more complex. Since meiosis reduces the number of chromosomes, it cannot be repeated and so does not take part in a cell division cycle.
The following is multiple choice question (with options) to answer.
Meiosis, like mitosis, is preceded by the duplication of what? | [
"neutrons",
"chloroforms",
"chromosomes",
"ribosomes"
] | C | |
SciQ | SciQ-2873 | optics, visible-light, wavelength
Title: Why we can't see objects smaller than wave length of light? I would like to ask, why we can't see objects smaller than wave length of light under traditional microscope. I know that there is some way to see them and the scientists who discover this.
Why we can't see objects smaller than wave length of light?
And who were these scientists?
I would like to ask, why we can't see objects smaller than wave length of light under traditional microscope.
The wavelength of light is any wavelength. There's visible light (which is what I think you mean) and then there's every possible wavelength above and below that.
Our eyes don't detect light (electromagnetic radiation) outside of the visible region (hence the name :-)) but we can use and do machines to detect these wavelengths and you've probably experienced them : X-ray machines, UV lights for security purpose, infra-red lights for remote controls.
Whatever wavelength you use is going to diffraction limited for resolution. As this detailed article explains, the limit for resolution (and that's assuming everything else is optimal) is about half the wavelength used.
Optical microscopes are designed for the visible wavelengths of light and focus light outside of this region well. You can use special optics designed for that purpose if your interest is outside of visible light.
The development and use of microscopes, not just visible light microscopes, is called Microscopy. That link should provide you with enough information to start with.
I know that there is some way to see them and the scientists who discover this.
Beyond light microscopes, scientists developed the electron microscope and later the scanning tunneling microscope. The principles of these devices are explained at those links.
The 1986 Nobel prize for Physics was shared between three people for their work on these inventions. Another man, Hans Busch, had made a major contribution to the design of the electron microscope but died in 1984 and the Nobel Prize is never awarded posthumously, so even if the committee had thought it appropriate to award him, the rules would have forbidden it.
The following is multiple choice question (with options) to answer.
The invention of what instrument in the 1930s allowed scientists to see viruses for the first time? | [
"electron microscope",
"magnifying glass",
"telescopes",
"spy glass"
] | A | Scientists did not actually see viruses for the first time until the 1930s. That’s when the electron microscope was invented. In 1915, English bacteriologist Frederick Twort discovered bacteriophage , the viruses that attack bacteria. He noticed tiny clear spots within bacterial colonies, and hypothesized that something was killing the bacteria. The tobacco mosaic virus shown in Figure below was the first one to be seen. |
SciQ | SciQ-2874 | genomics
In the case of a single gene with a single copy on both the maternal and paternal chromosomes, the Punnet Square accurately estimates the probably of inheriting each possible genotype. (50% chance of getting one of two alleles from dad * 50% chance of getting one of two alleles from mom). In the case of multiple genes on different chromosomes, the 50% chance of any given allele still holds, as all the genes segregate independently. The accuracy of the Punnet Square fails when genes are sufficiently close to each other on the same chromosome. Genes distant from each other on the same chromosome still segregrate independently due to a high level of recombination events between chromosomes in meiosis I, but genes in close physical proximity no longer segregate independently. The closer two genes are physically the more they tend to co-segregate. This tendency is reported empirically as a "distance" in centiMorgans and is related to physical distance in base pairs (kB or mB) but is not completely proportional to physical distance due to the existence of recombination "hot spots."
It's important to note that is accurately predicts genotypic ratios, but not necessarily phenotype. Phenotypes can be less than 100% penetrant, can cause embryonic lethal, epistasis, etc. Such that the observed phenotypic ratio does not match the predicted ratio. (For example, if YY was known to be 100% embryonic lethality, live births -> observed phenotypes instead be expected at 1/3 of each of the remaining genotypes. If Y was instead phenotypically dominant (one copy of Y determines phenotype), then 75% of children would be expected to be phenotypically Y (genotypically, the Y phenotypic children would be expected to distribute evenly between YO, YY, BY).
The following is multiple choice question (with options) to answer.
What is the name of the chart that allows you to easily determine the expected percentage of different genotypes in the offspring of two parents? | [
"periodic square",
"punnett square",
"Trafalgar Square",
"DNA helix"
] | B | A Punnett square is a chart that allows you to easily determine the expected percentage of different genotypes in the offspring of two parents. An example of a Punnett square for pea plants is shown in Figure below . In this example, both parents are heterozygous for flower color ( Bb ). The gametes produced by the male parent are at the top of the chart, and the gametes produced by the female parent are along the side. The different possible combinations of alleles in their offspring are determined by filling in the cells of the Punnett square with the correct letters (alleles). At the link below, you can watch an animation in which Reginald Punnett, inventor of the Punnett square, explains the purpose of his invention and how to use it. http://www. dnalc. org/view/16192-Animation-5-Genetic-inheritance-follows-rules-. html. |
SciQ | SciQ-2875 | crystal-structure, density-functional-theory, crystallography
Title: How can I find the smaller symmetric structure from big crystal unit cell? I have Pyrope (Mg3Al2(SiO4)3) crystal structure, downloaded from materialsproject:
https://materialsproject.org/materials/mp-6073/#
It appeared as triclinic cell, but if you download CIF file and open it from softwares like Avogadro or VESTA, it appeared as a orthogonal simple cubic (a=b=c, alpha = beta = gamma = 90 degree). I also checked that this geometry is the same with what I downloaded from American Mineralogy Material Database.
Now, I wish to run DFT or quantum calculations for them. So, I excluded atoms in periodic boundary, unit cell contains total 160 atoms. I'm afraid this might be too big, might takes too long time to calculate via DFT or any other quantum simulations. All I need to do is just geometry optimizations, but still, 160 atoms seems too big.
Using VESTA or Avogadro or any other software, is this possible to find the symmetric structure inside this or other "big" unit cell, and make a smaller / simpler version of unit cell for faster calculation?
Or, can I manually cut this unit cell in 1/4 size, 40 atom system with 1/2 size for x, y, and z direction, and run the minimization? It seems that the Pyrope unit cell have some sort of repeating structure inside the big unit cell. But I'm not sure if it is "safe" to find symmetry and divide the unit cell manually.
Thank you No, the unit cell is the smallest translational repeating unit, and any truncation of that would mean that you're calculating a different solid which may or may not exist.
160 atoms is a decent sized unit cell, but is still routinely doable with the right resources. (The materials project page you link to is in fact an automated DFT geometry optimization of that solid, so you could use that)
If you still want to do the calculation yourself then you have to use the whole cell; however, if the unit cell has some additional symmetry (e.g. center of inversion), then a good DFT program will take advantage of that to speed up the calculation.
The following is multiple choice question (with options) to answer.
What is the functional unit of compact bone? | [
"collagen",
"spongin",
"scleroprotein",
"osteon"
] | D | Compact bone makes up the dense outer layer of bone. Its functional unit is the osteon . Compact bone is very hard and strong. |
SciQ | SciQ-2876 | atomic-physics
Title: What gives covalent bond its strength? I came across the following passage from Structure and Properties chapter of Morrison-Boyd Organic Chemistry:
What gives the covalent bond its strength? It is the increase in electrostatic attraction. In the isolated atoms, each electron is attracted by-and attracts-one positive nucleus;in the molecule, each electron is attracted by two positive nuclei.
However, I don't think it refers to the force holding each atom together. It rather, merely describes the increase in the electrostatic force of attraction between the electrons and the nuclei. I believe that bond strength is a measure of the difficulty in pulling apart the component atoms, not the electrons from the positive nuclei.
What exactly is the pattern or picture of the forces on the nuclei and the electrons, due to one another, that holds the component atoms together? (I am aware that the decrease in overall energy or increase in stability is definitely not a reason to account for the strength of covalent bond, but rather a consequence of the action of such forces.) It probably helps to define what a covalent bond really is. Covalent bonds occur when one or more Atomic Orbitals (AO) of the participating atoms constructively interact and form a (bonding) Molecular Orbital (MO). The figure below schematises the formation of a $\sigma_{ss}$ MO when two hydrogen atoms combine to form a dihydrogen molecule:
The following is multiple choice question (with options) to answer.
Because the nuclei of each h atom contain protons, the electrons in the bond are attracted to the nuclei (opposite charges attract). but because the two atoms involved in the covalent bond are both h atoms, each nucleus attracts the electrons by the same amount. thus the electron pair is equally shared by these? | [
"four atoms",
"one atom",
"two atoms",
"nine atoms"
] | C | Because the nuclei of each H atom contain protons, the electrons in the bond are attracted to the nuclei (opposite charges attract). But because the two atoms involved in the covalent bond are both H atoms, each nucleus attracts the electrons by the same amount. Thus the electron pair is equally shared by the two atoms. The equal sharing of electrons in a covalent bond is called a nonpolar covalent bond. Now consider the HF molecule:. |
SciQ | SciQ-2877 | genetics
So the modern definition of a phenotype is the observable characteristics of an organism, anatomical, physiological or behavioral. The first 2 points are easily accepted and uncontroversial. But there is debate about what exactly should be included in "behavior". I'm going to ignore behavior for now.
An important point, and I think this is where there is disagreement between Remi.b and me, is that a phenotype must have a genetics basis. I realize this is not explicitly mentioned in any definition, but that is very much the way people mean it. And if not, the definition is totally meaningless. Take the example of a monkey missing a finger congenitally. This is a phenotype, it is due to its genes. If the monkey is missing a finger due to a fight, this is not a phenotype because genes have nothing to do with it (again, ignoring behavior for now).
So, in my opinion, what would not be a phenotype is something that you could conclusively prove to have no genetics basis whatsoever. That's an extremely (impossible) hard case to make. But in retrospect I was perhaps to quick to include behavior in the definition, and this is due to my own biases as a behavioral neuroscientist.
I think this is the narrow definition of phenotype and I don't think anyone would disagree up to that point. You might notice that there has been no mention of evolution so far. It is because genetics and evolution have been developed independently, and even though everybody was quite aware they must be 2 sides of the same coin evolution is not directly relevant to the genotype/phenotype distinction.
The following is multiple choice question (with options) to answer.
What is the term for when the phenotype of offspring is partly determined by the phenotype of its mother, irrespective of genotype? | [
"maternal effect",
"oceanic effect",
"uterine effect",
"congenital effect"
] | A | Gap genes themselves are under the effect of maternal effect genes, such as bicoid and nanos. Gap genes also regulate each other to achieve their precise striped expression patterns. The maternal effect is when the phenotype of offspring is partly determined by the phenotype of its mother, irrespective of genotype. This often occurs when the mother supplies mRNA or proteins to the egg, affecting early development. In developing Drosophila, maternal effects include axis determination. |
SciQ | SciQ-2878 | botany
Title: Do any plants exhibit hormonal changes similar to puberty? Just what the title states.
Are there any plants/trees that exhibit a growth spurt at a definite interval after the shoot appears? In flowering plants (the angiosperms) there are several developmental transitions in the life of the plant. I won't list the plants, because the list includes pretty much all of them (although the magnitude in the change of developmental pace differs widely between taxa and environments).
First there is seed germination, which is controlled hormonally. Absence of germination is usually imposed by abscisic acid, whilst germination is caused at the appropriate time by gibberellic acid and ethylene (among other things; Holdsworth, Bentsink & Soppe, 2008).
Next, in many herbaceous species there is a transition between a spreading growth stage (e.g. rosette growth) and the flowering stage. The 'growth spurt' here is the differentiation and elongation of the flowering stem, and then subsequently the sudden flowering of buds. The transition is also controlled hormonally, by a variety of hormones including auxin (Zhao, 2010), gibberellic acid, ethylene (Schaller, 2012), and the long anticipated, recently confirmed florigen (Choi, 2012). Ethylene and abscisic acid then play important roles in the next developmental transition when seeds and fruits are produced and dehisced.
Small RNAs are also now being revealed to play a large role in controlling the timing of developmental, but they are upstream of the hormonal changes. In particular some key miRNAs are involved in auxin-based regulation of branching, and in embryogenesis (Nodine & Bartel, 2010), and RNA silencing is involved in the switch from rosette growth to flowering growth (reviewed in Poethig, 2009 and Baurle & Dean 2006).
The following is multiple choice question (with options) to answer.
Natural methods of asexual reproduction, such as cuttings or budding, include strategies that plants have developed to perform what? | [
"iso-propagation",
"self-propagation",
"multi-propagation",
"mono-propagation"
] | B | Natural Methods of Asexual Reproduction Natural methods of asexual reproduction include strategies that plants have developed to self-propagate. Many plants—like ginger, onion, gladioli, and dahlia—continue to grow from buds that are present on the surface of the stem. In some plants, such as the sweet potato, adventitious roots or runners can give rise to new plants Figure 32.25. In Bryophyllum and kalanchoe, the leaves have small buds on their margins. When these are detached from the plant, they grow into independent plants; or, they may start growing into independent plants if the leaf touches the soil. Some plants can be propagated through cuttings alone. |
SciQ | SciQ-2879 | reaction-mechanism, everyday-chemistry, electrochemistry
Title: What Type of Gas Would Vinegar and Epsom Salt Create Under Electrolysis? I'm restoring a motorcycle and have a small homemade DIY zinc plating operation which consists of vinegar, epsom salt, a piece of zinc and a power supply.
When I plate a steel piece such as a bolt or small hardware piece, the piece in the solution starts forming small bubbles and it appears to be "gassing off" something. I was wondering what type of gas this may be and if it's harmful to breathe. You're most likely forming $\ce{H2}$ gas at the part.
If you're plating anywhere above about $2~\mathrm V$, that is probably sufficient overpotential to cause part of the passed current to go toward electrolysis of water.
There is negligible toxicity hazard to inhaling the small amounts of hydrogen that would be generated from an electrolytic cell on this scale.
There's a small ignition hazard if anything sparks near electrolyte of the plating cell as it's operating, but as long as you're not running it inside a tightly closed, small space you should have nothing to worry about with how small the cell is.
The following is multiple choice question (with options) to answer.
Many metals react with acids to produce what gas? | [
"mercury",
"helium",
"hydrogen",
"neon"
] | C | Many metals react with acids to produce hydrogen gas. A certain reaction produces 86.5 L of hydrogen gas at STP. How many moles of hydrogen were produced?. |
SciQ | SciQ-2880 | biophysics, cell-membrane
Title: Why doesn't the cell membrane just...break apart? Forgive me if this is a silly question. I can't understand the basics. Why doesn't the cell membrane just break apart? What's keeping the layers in the phospholipid bilayer together? I know that the membrane is embedded with proteins and lipids, but I still can't wrap my head around the "why". Are the hydrophobic interactions in the middle "stronger" than the hydrophilic interactions on the outside? What's keeping the individual phosphate heads together instead of, say, one of them just drifting away due to a nearby water molecule? The membrane bilayer is held together by hydrophobic forces. This is an entropy driven process. When a greasy or hydrophobic molecule is suspended in water, the water molecules form an organized "cage" around the hydrophobic molecule. When two hydrophobic molecules come into contact, they force the water between them out. This increases the entropy because the freed waters don't need to be organized into the cage. Lipid bilayers have many many many hydrophobic lipids that squeeze out a lot of water and greatly increase entropy. The polar phosphates allow the water to interact with the surface of the membrane, without a polar head group the lipids would form a spherical blob instead of a membrane.
Read this section on wikipedia for more.
The following is multiple choice question (with options) to answer.
What is the process of a cell membrane surrounding a particle and engulfing it calles? | [
"mitosis",
"phagocytosis",
"active transport",
"ingestion"
] | B | Figure 5.20 In phagocytosis, the cell membrane surrounds the particle and engulfs it. (credit: Mariana Ruiz Villareal). |
SciQ | SciQ-2881 | geology, paleontology, dating, history-of-science
Title: Did geologists determine the age of rocks and fossils before the advent of modern scientific dating methods? Did geologists determine the age of rocks and fossils before the advent of modern scientific dating methods such as radiometric, electron spin resonance and thermoluminescence?
If they did, does anyone know how they went about it? The approach adopted by Charles Lyell (and other writers in a similar timeframe), in his book 'Principles of Geology' which was first published in the 1830s was to look at processes in the modern landscape where the rate of change could be determined by observation or from historical evidence, and assuming that similar processes operated at similar rates in the geological past. So, for instance, if you measure the amount of sediment transported by a river today, and you measure the volume of sediment in that river's delta, you can estimate how long that delta took to form. If you see a similar delta in the geological record, you can assume it took a similar time to form. Lyell's estimates of the age of the earth were low, but as the concept of plate tectonics, with it's progressive recycling of rocks through subduction wasn't recognised, it was remarkably prescient.
The following is multiple choice question (with options) to answer.
What type of rocks are very useful for determining the deformation history of an area? | [
"igneous",
"limestone",
"sedimentary",
"crystalline"
] | C | Sedimentary rocks are very useful for determining the deformation history of an area. |
SciQ | SciQ-2882 | dating
Title: Can we carbon-date the remains of homo floresiensis found in 2003? According to the Wikipedia article on the species Homo floresiensis, the remains discovered in 2003 consist of unfossilized bones. I would assume that means they are still composed of the original organic material left behind when the human specimen died thousands of years ago. Shoudn't that mean radiocarbon dating would be a good method to date the reamains?
Many articles on Homo floresiensis also discuss how the remains were originally dated to ~12,000 years ago, but that this estimate was later revised to 60–100,000 years ago. However, everything I can find indicates that mostly geological dating methods were used, not radiometric dating.
Why not? The Wikipedia entry on carbon dating says that it can only be used reliably to date specimens up to ~50,000 years, but could carbon dating then at least place a lower limit on the age of these remains? And why wouldn't it have been used back when they thought the specimens were only ~12,000 years old? ScienceMag says:
The following is multiple choice question (with options) to answer.
What is the term for dating a rock based on composition decay? | [
"safe dating",
"radioactive dating",
"carbon dating",
"fuel dating"
] | B | There are other forms of radioactive dating. Rocks, for example, can sometimes be dated based on the decay of 238 U . The decay series for 238 U ends with 206 Pb , so that the ratio of these nuclides in a rock is an indication of how long it has been since the rock solidified. The original composition of the rock, such as the absence of lead, must be known with some confidence. However, as with carbon-14 dating, the technique can be verified by a consistent body of knowledge. Since 238 U has a half-life of solidified about. |
SciQ | SciQ-2883 | neuroscience, physiology, human-physiology, reflexes
Title: Are there neuron mediated reactions faster than reflexes? I'm interested in how fast the human body can respond to a stimulus. I know the fastest reflex, the blink reflex, operates around 100ms from stimulus to reaction. I also know that the blink reflex is known as the fastest reflex in the human body. My interest is in the fastest responses to stimuli I can find in the body.
Are there any faster responses to stimuli within the human body which use neurons but are not categorized as a reflex (due to some technicality), meaning they could be faster than the fastest reflex? To the best of my understanding a reflex is defined by the use of neurons to convey the information, I'm just wondering if there are any grey areas which don't qualify as a reflex but may be faster. I don't want to potentially write off an entire class of neurological behavior in my research simply because I stopped at the blink reflex. A reflex as fast as the blink in a neural circuit:
I would consider suppression of outer hair cells in the cochlea to be a reflex; the faster component of this reflex is about the same as the blink reflex, around 100 ms. The hair cells themselves aren't considered neurons, but the pathway that suppresses their motility certainly is.
A much much faster non-neuronal "reflex":
That said, the outer hair cells themselves also dance along quite fast in response to sensory input, even faster than the typical hearing range for humans, faster than 20kHz! In some ways, this is a reflex because you are taking sensory (specifically, auditory) information and turning it into a motor response, but all the "action" is taking place within one cell, and it isn't a neuron.
A more classical reflex that is substantially faster than 100 ms
Reflexes in the periphery can be much faster than 100 ms. The myotatic reflex, or stretch reflex, can be as fast as 30 ms in the knee - this is the reflex that is tested when a physician smacks you on the knee with a hammer (used as a test of spinal and peripheral nerve function, not as a punishment). It's likely there are other stretch reflexes that are faster just because distances to the spinal cord are shorter, but these might be more difficult to test (in this paper they report latencies as fast as 20 ms).
The following is multiple choice question (with options) to answer.
What is the term for a very rapid motor response that is not directed by the brain? | [
"instinct",
"adaptation",
"reflex",
"sensor"
] | C | The somatic nervous system also controls some unconscious movements called reflexes. A reflex is a very rapid motor response that is not directed by the brain. In a reflex, nerve impulses travel to and from the spinal cord in a reflex arc, like the one in Figure below . In this example, the person jerks his hand away from the flame without any conscious thought. It happens unconsciously because the nerve impulses bypass the brain. |
SciQ | SciQ-2884 | genetics
Title: How does chromosome cross-over occur? I have heard that during meiosis, homologous chromosomes from each parent "cross-over", which enables the off-spring to inherit some alleles from the mother and some alleles from the father. The picture below illustrates this "cross-over", but of course this must occur at multiple sites, rather than just the one shown in the picture.
Now my question is what causes the chromosomes to align perfectly during cross-over so that the loci of a particular gene will substitute for the corresponding loci on the homologous chromosome, as opposed to being substituted with a completely random locus? Does each gene have a unique non coding sequence before it specifying what gene it is to enable this process to occur? Quite simply, because chromosome pairing is sequence specific. Holliday Junctions, which are the functional structures of a cross-over, occur through a process called "strand invasion," during which a region of one chromosome physically base-pairs with that of another. Thus one locus cannot pair with a random locus, as there is generally insufficient sequence complimentarity between two random regions to form a functional Holliday Junction. One interesting consequence of this mechanism is gene duplication and deletion in repetitious regions of the chromosome. For example, genes with large repeated regions, such as the gene responsible for Huntington's disease, can expand and contract during homologous recombination due to strand invasion occurring at non-equivalent, but still homologous, sites. Wikipedia does a nice job going over homologous recombination. I also recommend looking over the relevant sections in Molecular Biology of the Cell, available on the PubMed Bookshelf.
The following is multiple choice question (with options) to answer.
Crossover occurs between non-sister chromatids of which chromosomes? | [
"homologous",
"analogous",
"identical chromosomes",
"compound chromosomes"
] | A | Figure 11.3 Crossover occurs between non-sister chromatids of homologous chromosomes. The result is an exchange of genetic material between homologous chromosomes. |
SciQ | SciQ-2885 | water, elements
Title: Chemical composition of seawater Is it true that the sea water is composed of about $86\%$ oxygen, $11\%$ hydrogen and $3\%$ of minerals? The chemical formula of water is $\ce{H2O}$ (two hydrogen and one oxgen) that shows that the number of hydrogen is greater than that of oxygen.
If the number of hydrogen is greater, then why does the sea water consist of $11\%$ hydrogen and $86\%$ oxygen, which is lesser than the oxygen?
The book which I am reading says which is confusing me:
... Seawater is composed of about $86\%$ oxygen, $11\%$ hydrogen and $3\%$ of minerals, consisting mainly of sodium and chlorine. The book that you're reading is measuring by mass.
If you have pure water then you would expect oxygen to make up $\frac{16}{16 + 2}\times 100\% \approx 89 \% $ by mass. Likewise, hydrogen would make up $\frac{2}{16 + 2}\times 100\% \approx 11 \% $ by mass.
The following is multiple choice question (with options) to answer.
Water is an oxide of what element? | [
"hydrogen",
"carbon",
"nitrogen",
"helium"
] | A | Carbon dioxide is an oxide of carbon, while water is an oxide of hydrogen. Early scientists viewed oxidation as a process in which a substance was reacted with oxygen to produce one or more oxides. In the previous examples, magnesium and methane are being oxidized. |
SciQ | SciQ-2886 | neuroscience, brain, neurophysiology
Title: What are Intersensory Associations? While I was reading about "Neural Control and Coordination" I came across this
"Association areas in the forebrain are responsible for complex functions like intersensory associations, ....."
What are "intersensory associations"? I have searched the net but could not find anything useful. A more common terminology regarding 'intersensory associations' is multisensory or crossmodal integration. Crossmodal integration takes place in the association cortices in the brain (Fig. 1). An example is the coupling of auditory and visual input during lip reading, as mentioned in the comments. Lip reading can aid in acoustic speech understanding, especially so in the hearing impaired.
The association cortices include most of the cerebral surface of the human brain and are responsible for integrating the sensory input that arrives in the primary sensory cortices. The diverse functions of the association cortices are loosely referred to as “cognition,” which literally means the process by which we come to know the world. Cognition enables us to attend to external stimuli, to identify the significance of stimuli and to plan meaningful responses to them. The association cortices receive and integrate information from a variety of sources and in turn influence a range of cortical and subcortical targets (Purves et al., 2001).
Fig. 1. Association cortices. source: Brown, Physiology & Neuroscience websites
Reference
- Purves et al., Neuroscience, 2nd ed. Sunderland (MA): Sinauer Associates; 2001
The following is multiple choice question (with options) to answer.
What term is used to describe the parts of the brain involved in the reception and interpretation of sensory stimuli collectively? | [
"medulla oblongata",
"neurons",
"sensorium",
"glial cells"
] | C | Sensorium Those parts of the brain involved in the reception and interpretation of sensory stimuli are referred to collectively as the sensorium. The cerebral cortex has several regions that are necessary for sensory perception. From the primary cortical areas of the somatosensory, visual, auditory, and gustatory senses to the association areas that process information in these modalities, the cerebral cortex is the seat of conscious sensory perception. In contrast, sensory information can also be processed by deeper brain regions, which we may vaguely describe as subconscious—for instance, we are not constantly aware of the proprioceptive information that the cerebellum uses to maintain balance. Several of the subtests can reveal activity associated with these sensory modalities, such as being able to hear a question or see a picture. Two subtests assess specific functions of these cortical areas. The first is praxis, a practical exercise in which the patient performs a task completely on the basis of verbal description without any demonstration from the examiner. For example, the patient can be told to take their left hand and place it palm down on their left thigh, then flip it over so the palm is facing up, and then repeat this four times. The examiner describes the activity without any movements on their part to suggest how the movements are to be performed. The patient needs to understand the instructions, transform them into movements, and use sensory feedback, both visual and proprioceptive, to perform the movements correctly. |
SciQ | SciQ-2887 | bond, electrons, lewis-structure, valence-bond-theory
Let's next examine the situation in $\ce{O2}$. Here is the molecular orbital diagram for $\ce{O2}$. As we again fill the orbitals with electrons according to the Aufbau Principle we again arrive at the point where we have two electrons remaining and the next available molecular orbital is the $\ce{\pi^{x}_{g}}$. But we see that there is a second orbital at exactly the same energy (degenerate) and it is the $\ce{\pi^{y}_{g}}$ orbital. According to Hund's Rule, rather than put both electrons into one of these orbitals, we place just one electron in each of these two degenerate orbitals. So while
$\ce{O2}$ does have two non-bonding electrons, they are not paired up - there is no lone pair, these electrons exist in separate orbitals and $\ce{O2}$ consequently has a triplet ground state resulting from these two unpaired non-bonding electrons.
So sometimes a non-bonding pair of electrons will exist as a lone pair (as in the case of water), sometimes they won't exist as a lone pair as in the case of oxygen. To solve these kinds of problems one must know (or guess) the structure of the molecule and then determine the molecular orbital arrangement. Then, when we fill these orbitals with electrons we will see if any non-bonding electrons will exist as a lone pair in a single orbital, or if the two non-bonding electrons will exist in separate orbitals and remain unpaired.
The following is multiple choice question (with options) to answer.
Experiments show that each o2 molecule has two unpaired what? | [
"neutrons",
"quarks",
"protons",
"electrons"
] | D | Experiments show that each O2 molecule has two unpaired electrons. The Lewis-structure model does not predict the presence of these two unpaired electrons. Unlike oxygen, the apparent weight of most molecules decreases slightly in the presence of an inhomogeneous magnetic field. Materials in which all of the electrons are paired are diamagnetic and weakly repel a magnetic field. Paramagnetic and diamagnetic materials do not act as permanent magnets. Only in the presence of an applied magnetic field do they demonstrate attraction or repulsion. |
SciQ | SciQ-2888 | acid-base
Title: What makes protons give the property of acidity? Brønsted Lowry definition of an acid says that an acid gives away protons.
What I don't understand is what makes dissolved protons grant the property of acidity? Like, why would dissolved protons eat up materials?
My question applies to bases too, I suppose. And I guess you could include Lewis-acids and bases in your argumentation...
It's a question that has been bothering me for long. By the way I am not chemist(nor do I study chemistry). Whether something is a Brønsted acid is defined by its pH.
$$pH = -log_{10}[H^+]$$
In other words, the better a substance is at releasing protons, the higher the concentration of protons [H+], and correspondingly the lower its pH.
Whereas for Lewis acid, it is the ability for it to strip electrons from anything it attacks (electrophilicity). There is no direct measurement for the strength of Lewis acidity, as many factors have to be taken into consideration, such as enthalpy change, steric factors. In fact, many substances can act as Lewis acids can also act as Lewis bases, such as water, ammonia, and even some alkanes.
Ultimately, what makes acids and bases so corrosive is its ability act as an oxidant or reductant.
Oxidation: Lose electrons/Gain hydrogen.
Reduction: Gain electrons/Lose hydrogen.
The following is multiple choice question (with options) to answer.
Acidity is measured by what physical property? | [
"amp",
"ps",
"kω",
"ph"
] | D | A solution is a mixture of two or more substances that has the same composition throughout. Some solutions are acids, some are bases. |
SciQ | SciQ-2889 | biochemistry, proteins, enzymes, digestive-system, digestion
Title: Betaine HCl stomach pH It seems betaine HCL is often recommended for those suffering from "low stomach acid" -- which, as I understand, is having too high stomach pH for proper digestion (especially for proteolysis via pepsin). However, I have a few questions then -- though I'm not sure if my reasoning is correct here:
Understandably, one wouldn't want to drink pure or highly concentrated HCl by itself to increase stomach acid! But then, what role does the betaine play?
I'm guessing betaine HCl probably does not dissolve in water to give the same pH as just straight (or concentrated) hydrochloric acid -- since then it would seem just as dangerous as drinking plain HCl!
In that case, if it doesn't decrease the pH as much, making it safe for oral consumption, what value does it bring for "lowering stomach pH" anyway? I mean, one could just drink a little vinegar or citric acid for the same effect?
Or, perhaps, is betaine-HCl just a means of some "delayed release" of HCl to lower stomach pH without hurting the mouth and esophagus during its initial consumption? Betaine may just be a useful carrier here, given it's quaternary ammonium and carboxylic acid groups (e.g., a zwitterionic carrier)
Alternatively, could the value of betaine HCl simply be in providing a source of Cl- anions, possibly for increased pepsin activity? (I'm not sure if pepsin requires merely low pH or specifically also needs Cl- anions as well) Betaine-HCl does seem to be often formulated with additional pepsin enzyme(s) as well... Betaine HCl (trimethylglycine) was present in over the counter "stomach acidifiers" but the US FDA says there is no evidence for its efficacy and has banned its use for this indication (source: US FDA) - it may be freely available elsewhere, I am unaware of the regulatory status in other jurisdictions.
The following is multiple choice question (with options) to answer.
Antacids are bases that neutralize what in the digestive tract? | [
"salts",
"fats",
"hormones",
"acids"
] | D | Antacids are bases that neutralize acids in the digestive tract. Magnesium hydroxide [Mg(OH)2] is one such antacid. It reacts with hydrochloric acid in the stomach according to the following reaction: Mg(OH)2 + 2HCl → MgCl2 + 2H2O How many grams of HCl can a 200 mg dose of Mg(OH)2 neutralize?. |
SciQ | SciQ-2890 | terminology, meteorology
I've tried to illustrate the relationships with insolation and temperature here:
There are some other ways too:
Ecological. Scientists who study the behaviour of organisms (hibernation, blooming, etc.) adapt to the local climate, sometimes using 6 seasons in temperature zones, or only 2 in polar and tropical ones.
Agricultural. This would centre around the growing season and therefore, in North America and Europe at least, around frost.
Cultural. What people think of as 'summer', and what they do outdoors (say), generally seems to line up with local weather patterns. In my own experience, there's no need for these seasons to even be 3 month long; When I lived in Calgary, summer was July and August (hiking), and winter was December to March (skiing). Here's another example of a 6-season system, and a 3-season system, from the Aboriginal people of Australia, all based on weather.
Why do systems with later season starting dates prevail today? Perhaps because at mid-latitudes, the seasonal lag means that the start of seasonal weather is weeks later than the start of the 'insolation' period. In a system with no heat capacity, there would be no lag. In systems with high heat capacity, like the marine environment, the lag may be several months (Ibid.). Here's what the lag looks like in three mid-latitude cities:
The exact same effect happens on a diurnal (daily) basis too — the warmest part of the day is often not midday (or 1 pm in summer). As with the seasons, there are lots of other factors too, but the principle is the same.
These aren't mutually exclusive ways of looking at it — there's clearly lots of overlap here. Cultural notions of season are surely rooted in astronomy, weather, and agriculture.
The following is multiple choice question (with options) to answer.
What is the climate of a small area called? | [
"biome",
"ecosystem",
"microclimate",
"microevolution"
] | C | Climate conditions in a small area may be different from those of the surroundings. The climate of the small area is called a microclimate . The microclimate of a valley may be cool relative to its surroundings since cold air sinks. The ground surface may be hotter or colder than the air a few feet above it. This is because rock and soil gain and lose heat readily. Different sides of a mountain will have different microclimates. In the Northern Hemisphere, a south-facing slope receives more solar energy than a north-facing slope. Each side supports different amounts and types of vegetation. |
SciQ | SciQ-2891 | genetics, population-genetics, mutations
Title: Can the mutation rate vary for individuals of the same species, growing in similar environments? Suppose we consider several populations who originally inherited their genome from the same ancestor, and that we put for a few thousands generations in similar environments.
Could the mutation rate vary between the different populations or within the same population, but between different time points? Yes.
between individuals: https://academic.oup.com/mbe/article/34/2/419/2528250
between individuals: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4617969/
hypermutation (transient): https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1087688/
The following is multiple choice question (with options) to answer.
The rate of what process depends on how many of an organism’s genes have changed over a period of time and on the generation time of a particular species? | [
"respiration",
"photosynthesis",
"digestion",
"evolution"
] | D | The rate of evolution depends on how many of an organism’s genes have changed over a period of time. Evolution is usually so gradual that we do not see the change for many, many generations. The rate of evolution also depends on the generation time of a particular species. |
SciQ | SciQ-2892 | optics, visible-light, terminology, geometric-optics, lenses
If the position of P' is also displaced tangentially relative to CP (along the tangent to the circle of radius CP), the distortion is said to be tangential.
No, it isn't. I modified the above function to show the "tangential" displacement of points that are on a circle.
function tangentialDistortionOnCircle (p1, p2)
radius = 10;
x = radius * cos(0:2*pi/20:2*pi);
y = radius * sin(0:2*pi/20:2*pi);
r = x.**2 + y.**2;
xy = x.*y*2;
quiver(x, y, xy*p1 + (r+2*x.**2)*p2, xy*p2 + (r+2*y.**2)*p1, 0);
axis([-radius-5 radius+5 -radius-5 radius+5 ], "square");
endfunction
Called with these parameters:
tangentialDistortionOnCircle(.007, .007)
gives this result
This doesn't look like a tangential displacement to me at all. If it was, it would look like a swirl around the center. But that's not the case. Take the position of a point P on the image relative to the geometric image center C. Assume C remains undistorted in the lens produced image, but P is distorted into P'.
If the position of P' is only distorted radially along direction CP, the distortion is said to be radial.
If the position of P' is also displaced tangentially relative to CP (along the tangent to the circle of radius CP), the distortion is said to be tangential.
See for instance "Camera Calibration with Distortion
Models and Accuracy Evaluation" (IEEE Transactions On Pattern Analysis And Machine Intelligence), especially Figs.2 & 3 (pg. 968) and Fig.4 (pg.969).
The following is multiple choice question (with options) to answer.
The sticky stigma at the tip of the carpel receives what? | [
"nitrogen",
"pollen",
"salt",
"bacteria"
] | B | |
SciQ | SciQ-2893 | newtonian-mechanics, forces, everyday-life, biophysics, weight
All of this makes it very complicated because you need to isolate what type of stress is under consideration. However, we can make some general observations.
Any vertical position will maximize compressive stress on the backbone. So standing and sitting straight up should maximize compressive stress. Why sitting down is more than standing up is not clear. Perhaps it has to do with concentrated stress that the reaction force of the seat imposes on the bottom of the spine (tail bone). Or perhaps sitting down causes more curvature of the spine, though I’m not sure.
Any horizontal position will minimize compressive, tensile and bending stress. So lying down should be less “stressful” on the backbone than all the other positions.
Sitting and leaning over would probably be the most stressful since bending of the backbone is maximized. This results in both tensile and compressive stress on the backbone.
Hope this helps.
The following is multiple choice question (with options) to answer.
Are the joints between the vertebrae contained in your backbone fully movable, partially movable, or unmovable? | [
"none of these",
"partially movable",
"unmovable",
"fully movable"
] | B | Partly movable joints allow only a little movement. Your backbone has partly movable joints between the vertebrae ( Figure below ). |
SciQ | SciQ-2894 | paleontology
Title: How to start studying dinosaurs and pre-historic mammals/sea creatures I'm kind new to this hole thing of dinosaurs that I'm really interested in, are there any good books/websites/webpages to study the biology of pre-historic creatures? Dinosaurs, mammals, fishes, anything that is not alive anymore. Also, any good books about the history of how these species evolved and the history behind them would be appreciated. Here's what it takes to really study this: you need to go through the whole bachelor program for geoscientists, that includes fundamental geodynamics like plate tectonics, magmatism, volcanism, volcanic and metamorphic rocks and generally the cycles that make up earth's internal dynamics.
Then there is the huge field of external factors, like sediment geology (that's really complicated stuff), weathering and transport and how soils come to being, diagenesis and the structures sediments can form and their classifications. Role of the ocean (that's where it starts, before all) and the atmosphere, of course.
When through that, usually 4 semesters or so, you can start to specialize. For paleontolgy you need knowledge of earth history, of course, it's subdivision, and the conditions at certain times as far as they are known. Once that's done, then comes real paleontology: Animals (invertebrates and vertebrates), plants, and their development, biological evolution (that's frequently underrated, I find), taphonomy, ... For a sturdy base count another 2-4 semesters.
You may see that even a bunch of websites, maybe all of them together, cannot replace actual study. I am not aware of any site that even gives a reasonable overview of the field. Geoscience, and thus paleontology, touch many fields of natural science.
That said, when asked "How to learn about animal paleontology ?" I allways mention Micheal Benton, Vertebrate Paleontology. It needs a basic understanding of geoscience, evolution and skeleton anatomy. Functional morphology, phylogeny and an overview over sediment geology and earth history also won't harm, but you could give it a try. Some things are explained in between.
The following is multiple choice question (with options) to answer.
Which branch of biology uses fossils to study life's history? | [
"zoology",
"geology",
"paleontology",
"morphology"
] | C | Paleontology, another branch of biology, uses fossils to study life’s history (Figure 1.12). Zoology and botany are the study of animals and plants, respectively. Biologists can also specialize as biotechnologists, ecologists, or physiologists, to name just a few areas. Biotechnologists apply the knowledge of biology to create useful products. Ecologists study the interactions of organisms in their environments. Physiologists study the workings of cells, tissues and organs. This is just a small sample of the many fields that biologists can pursue. From our own bodies to the world we live in, discoveries in biology can affect us in very direct and important ways. We depend on these discoveries for our health, our food sources, and the benefits provided by our ecosystem. Because of this, knowledge of biology can benefit us in making decisions in our day-to-day lives. The development of technology in the twentieth century that continues today, particularly the technology to describe and manipulate the genetic material, DNA, has transformed biology. This transformation will allow biologists to continue to understand the history of life in greater detail, how the human body works, our human origins, and how humans can survive as a species on this planet despite the stresses caused by our increasing numbers. Biologists continue to decipher huge mysteries about life suggesting that we have only begun to understand life on the planet, its history, and our relationship to it. For this and other reasons, the knowledge of biology gained through this textbook and other printed and electronic media should be a benefit in whichever field you enter. |
SciQ | SciQ-2895 | evolution, dna, mitochondria, plasmids, prokaryotes
Title: Why don't mitochondria have plasmids? According to the endosymbiotic theory, mitochondria are descended from specialised bacteria (probably purple nonsulfur bacteria) that somehow survived endocytosis by another species of prokaryote or some other cell type, and became incorporated into the cytoplasm [ref].
And plasmids naturally exist in bacterial cells, and they also occur in some eukaryotes [ref].
I was however taught that mitochondria have no plasmid and only have circular DNA. If the endosymbiotic theory is true, then how come mitochondria have no plasmid? The mitochondrial genome is highly reduced; many mitochondrial genes have been transferred to the nuclear genome (see endosymbiotic gene transfer) and therefore the mitochondria are fully dependent on the nucleus to function.
Bacteria need not necessarily have a plasmid. Usually, all the important genes are present in the chromosomal DNA. Since the mitochondria have lost most of their genes and retain only a few genes that are highly essential for their function, the likelihood of retention of any plasmid DNA is very low. However, there are some reports of plasmid-like DNA in mitochondria (mostly in plants).
Handa (2008): in Brassica
Robison et al., (2005): in carrots
Collins et al., (1981): in Neurospora (a fungus)
Likewise, chloroplasts also harbour plasmid-like DNA (google-scholar hits).
The following is multiple choice question (with options) to answer.
What do you call prokaryotes that do not need oxygen for respiration? | [
"aerobic",
"chloroflexus",
"enzymatic",
"anaerobic"
] | D | Anaerobic prokaryotes do not need oxygen. They use fermentation or other methods of respiration that don’t require oxygen. In fact, some cannot tolerate oxygen. An example is a bacterium that infects wounds and kills tissues, causing a condition called gangrene. |
SciQ | SciQ-2896 | climate-change, glaciology, ice-sheets
Title: Can ice caps reform if they disappear? Excuse my ignorance. I'm under the impression that there are various types of ice at the poles, but I don't know the difference or the significance of each type, so, in terms of whatever is actually melting in these areas as a result of climate change, is it possible that it could come back if greenhouse gas emissions were eliminated or something like that? Basically, I'm assuming that the ice caps are necessary in order to maintain the habitability of the planet for humans, so is there some sort of threshold of melting that would essentially count as a point of no return or is there always the possibility of seeing the ice caps return to safe levels? Yes, polar ice can melt -- significantly, if not completely, with substantial effects on human civilization. And it can stabilize and recover, but the question is at what pace relative to human civilization.
There are generally three types of polar ice:
Ice sheets: "An ice sheet is a mass of glacial land ice extending more than 50,000 square kilometers (20,000 square miles). The two ice sheets on Earth today cover most of Greenland and Antarctica."
Ice shelves: "Permanent floating sheets of ice that connect to a landmass."
Sea ice: "Sea ice is frozen ocean water. It forms, grows, and melts in the ocean. In contrast, icebergs, glaciers, and ice shelves float in the ocean but originate on land."
Sea ice is usually 1-2 meters thick; shelf ice is 100-200 meters thick; sheet ice is one to several kilometers thick.
The poles differ significantly. It's often pointed out that the Arctic is an ocean surrounded by land and the Antarctic is land surrounded by ocean. The North Pole is occupied by sea ice, about half of which melts every summer and reforms every winter.
At the other extreme are the ice "caps," more or less the ice sheets in Greenland and Antarctica that extrude ice in the form of glaciers and ice shelves that continuously flow into the ocean, breaking apart and melting.
To take just Greenland: Greenland has had some degree of glaciation for ~38 million years, but lost much or almost all of its ice during a warming period about 400,000 years ago, suggesting that the current ice sheet was created in that time.
The following is multiple choice question (with options) to answer.
When a glacier no longer moves, what is it called? | [
"an iceberg",
"a glacial lake",
"an ice sheet",
"an ice cylinder"
] | C | Glaciers are melting back in many locations around the world. When a glacier no longer moves, it is called an ice sheet. This usually happens when it is less than 0.1 km2 in area and 50 m thick. |
SciQ | SciQ-2897 | evolution, trees
Title: How related are trees? I was surprised to see how far apart macadamia and hazelnuts are from each other. I always thought all trees had a common ancestor that was also a tree. But that doesn't seem to be the case? Did wood evolve multiple times? The word "tree" is a not a taxonomic classification, but a human perceptual clustering based on form and size. The word "fish" has a similar problem, covering a vast collection of taxa, some of which are less closely related to one another than they are to us.
Becoming tree-like often has a strong evolutionary value, because plants compete for sunlight and taller plants shade shorter plants. Thus, we should not be surprised that "tree" forms have evolved independently in a number of different lineages.
The common evolutionary lineage for all of these, however, is tracheophyta, the vascular plants. These are plants that have differentiated xylem (which is the wood of a tree) and phloem tissues for transport of water and minerals. Most such plants are not trees, of course, but these tissues provide an effective means of vertical transport and the basis for hard woody material, which appears to have been the key differentiator between plants capable of evolving into trees and plants that are not able do to so.
The following is multiple choice question (with options) to answer.
What did roots evolve from that plants used for aborption? | [
"seeds",
"rhizoids",
"oomycetes",
"leguminous"
] | B | Roots are vascular organs that can penetrate soil and even rock. They absorb water and minerals from soil and carry them to leaves. They also anchor a plant in the soil. Roots evolved from rhizoids, which nonvascular plants had used for absorption. |
SciQ | SciQ-2898 | botany, plant-physiology, ecology, virology, host-pathogen-interaction
Note about symbiosis - comes in reaction to @Gerhard's comment
Different authors use the word symbiosis differently. From wikipedia:
The definition of symbiosis is controversial among scientists. Some believe symbiosis should only refer to persistent mutualisms, while others believe it should apply to any type of persistent biological interaction (i.e. mutualistic, commensalistic, or parasitic).4 After 130+ years of debate,5 current biology and ecology textbooks now use the latter "de Bary" definition or an even broader definition (i.e. symbiosis = all species interactions), with the restrictive definition no longer used (i.e. symbiosis = mutualism)
The following is multiple choice question (with options) to answer.
Although lots of symbiotic relationships help both organisms, sometimes one of the organisms is harmed. when that happens, the organism that benefits, and is not harmed, is called a what? | [
"parasite",
"child",
"infection",
"viruses"
] | A | Although lots of symbiotic relationships help both organisms, sometimes one of the organisms is harmed. When that happens, the organism that benefits, and is not harmed, is called a parasite . This type of relationship is known as parasitism. |
SciQ | SciQ-2899 | paleoclimatology
Has trees, i.e., long-lived woody plants that are capable of growing at least ten meters tall and that grow both upward by extending new branches and outward by widening of the trunk. Amongst other things, this rules out times before ~380 million years ago, which was when the first trees formed.
Has sufficient trees so as to constitute a forest, which I'll define as a largish area where trees grow sufficiently dense so as to form a more or less closed canopy. This distinguishes forests from areas with only a few trees such as savannas and krummholz.
Has very harsh winters, with at least one month where the average temperature is well below freezing, and temperatures of -40° C are not rare. This distinguishes boreal forests from cold oceanic forests such as the Magellanic subpolar forests in southern Chile and Argentina.
Has mild summers, with only a few months where the average temperature exceeds 10° C. This distinguishes boreal forests from hemiboreal and temperate forests. Note that some scientists do not make this distinction, classifying Köppen climate zone Dfb as boreal.
Is extensive. This distinguishes large boreal forests from high altitude subalpine forests that would locally pass the above tests. Subalpine forests can occur at any latitude, including Australia's Snow Mountains, New Zealand's Southern Alps, and parts of the Andes. This is not a clear-cut boundary. As a climate cools, subalpine forests may spread to the valleys between mountains and then spread out beyond the mountains. At some point, such montane forests becomes boreal forests.
The following is multiple choice question (with options) to answer.
What are named for major physical or climatic features and for their predominant vegetation? | [
"terrestrial biomes",
"geological formations",
"terrestrial substrates",
"celestial bodies"
] | A | |
SciQ | SciQ-2900 | identification, minerals
Title: How can chemists distinguish pure chemical element specimens that look almost "the same" as well as what deposit is what in a multimineral mined rock? As a non chemist I am most often charmed when visiting Wikipedia articles of chemical elements and see images of very pure specimens of element after element, proton by proton, and often also metal cube specimen made from smithing similar pure deposits.
The wiki article Periodic table allows me to do so easily; here are some elements I found looking almost the same and don't think I personally could distinguish between them without some instrument:
molybdenum and manganase
titanium and chromium
rutenium and cadmium
sodium and aluminium
silicone and germanium
The following is multiple choice question (with options) to answer.
Similarity of crystal structures is used to categorize what non-living materials? | [
"grains",
"corals",
"salts",
"minerals"
] | D | Mineralogists are scientists who study minerals. They divide minerals into groups based on chemical composition. Even though there are over 4,000 minerals, most minerals fit into one of eight mineral groups. Minerals with similar crystal structures are grouped together. |
SciQ | SciQ-2901 | endocrinology, glucose, homeostasis, insulin, hypothalamus
Title: Role of the Hypothalmus in the control of Blood Sugar In homeostatic regulation of blood glucose, the receptor and effector is the Pancreas, but how does the control centre — the Hypothalamus — connect and link into this process? Your question doesn’t make it clear whether you think that the pancreas must be under the control of the hypothalmus, or whether you are asking whether it has an influence on the pancreas in relation to the secretion of insulin and glucagon, which control the concentration of blood glucose.
First, it has been long known that secretion of insulin can be influenced by the concentration of glucose in isolated pancreatic islets in vitro, so it can not be true that the effects must involve the hypothalmus. This is implicit in most book or general information articles you might find on the web, but for an original reference a review by W.J. Malaisse in Diabetologia 9, 167–173 (1973) seems highly cited.
I know almost nothing about physiology, but on searching the web for the role of the hypothalmus in glucose homeostasis, found a most readable prize-winning postgraduate essay on the topic by Syed Hussein of Imperial College London. I trust that it is in order to append an edited extract of this:
The following is multiple choice question (with options) to answer.
Diabetes is a non-infectious disease in which the body is unable to control the amount of what in the blood? | [
"sugar",
"protein",
"water",
"plasma"
] | A | Diabetes is a non-infectious disease in which the body is unable to control the amount of sugar in the blood. People with diabetes have high blood sugar, either because their bodies do not produce enough insulin, or because their cells do not respond to insulin. Insulin is a hormone that helps cells take up sugar from the blood. Without enough insulin, the blood contains too much sugar. This can damage blood vessels and other cells throughout the body. The kidneys work hard to filter out and remove some of the extra sugar. This leads to frequent urination and excessive thirst. |
SciQ | SciQ-2902 | taxonomy
Title: Why are sponges sometimes not considered multicellular? I read somewhere (I can't find where) that there is no scientific consensus whether sponges should be considered multicellular organisms.
It seems I don't understand where is the line between unicellular and multicellular life.
I am not able to find a more elaborate explanation of that doubt. What are the reasons for it? Sponges are generally considered as colonial organisms because there is little cell specialization and little separation of function/role. All cells do pretty much the same thing; it looks more like a pile of individual cells than an actual multicellular organism. In reality it is a little bit in between.
In any case, what one wants to call multicellular or unicellular is a matter of definition and preferences. You cannot find the line between unicellular and multicellular because there is no such line that would not be very arbitrary and filled with special cases.
You can study a little more the physiology of sponges and then decide for yourself if it looks sufficiently like a multicellular organism or more like a colony of cells (a colonial organism).
The following is multiple choice question (with options) to answer.
All living organisms are classified into one of six broad categories called what? | [
"cities",
"nobles",
"kingdoms",
"tribes"
] | C | The level of biodiversity found in the fossil record suggests that the last few million years include the period of greatest biodiversity in the Earth's history. However, not all scientists support this view, since there is a lot of uncertainty as to how strongly the fossil record is biased by the greater availability and preservation of more recent fossil-containing rock layers. Some researchers argue that modern biodiversity is not much different from biodiversity 300 million years ago. Estimates of the present global species diversity vary from 5 million to 30 million species, with a best estimate of somewhere near 10 million species. All living organisms are classified into one of the six kingdoms: Archaebacteria (Archaea), Eubacteria (Bacteria), Protista (Protists), Fungi, Plantae (Plants), and Animalia (Animals). |
SciQ | SciQ-2903 | human-biology, cancer
Title: Why do most breast cancers occur in women? According to Korde et al. (2010):
Male breast cancer accounts for less than 1% of all cancers in men and less than 1% of breast cancers.
This raises the question: Why do most breast cancers occur in women?
Two plausible explanations I can think of:
A male is less likely to get breast cancer for anatomical reasons (such as a smaller quantity of breast tissue, or breast tissue that is less susceptible to cancer),
Women have higher significantly levels of estrogen, which is linked to mutations that cause breast cancer (see Cavalieria et al. (2006)).
Although, I have no evidence to suggest that either of these is predominant factor. Yes, this is mostly about estrogen. Most breast cancers rely on endogenous estrogen to sustain proliferation.
Some general reading: Cancer Medicine, Chapter 18
More in-depth reading: Endogenous Hormones as a Major Factor in Human Cancer
Requested summary of mentioned readings:
First of all, there is an established link between breast cancer cell proliferation and concentration of estrogens and progesterone, which is logical, because normal breast cells divide in response to those hormones (e.g. puberty, pregnancy, even luteal phase of the menstrual cycle). Secondly, the incidence of breast cancer in women correlates with major changes in their hormonal profile - girls and elderly women (i.e. women with lower levels of sex hormones) don't get breast cancer.
Many factors, that influence the risk of developing breast cancer are in fact tightly connected to the hormones' levels. For example - early age of menarche (or, more importantly, first ovulation, because physical activity at young age disturbs ovulation AND is protective against breast cancer) and Hormone Replacement Therapy raise the risk, early age of first full-term pregnancy or any form of artificial menopause (such as preventive oophorectomy for women with mutations in BRCA1 or 2) reduce the risk.
The first table from the book chapter lists known risk and preventive factors. The review article explains the same ideas, but connects them to other types of cancer (e.g. ovarian cancer) and suggests mechanisms, which might be the cause of those risk changes.
The following is multiple choice question (with options) to answer.
What is the most common type of cancer in adult males? | [
"stomach cancer",
"lung cancer",
"prostate cancer",
"liver cancer"
] | C | Cancer is usually found in adults, especially in adults over the age of 50. The most common type of cancer in adult males is cancer of the prostate gland. The prostate gland is part of the male reproductive system. Prostate cancer makes up about one third of all cancers in men. The most common type of cancer in adult females is breast cancer. It makes up about one third of all cancers in women. In both men and women, lung cancer is the second most common type of cancer. Most cases of lung cancer happen in people who smoke. |
SciQ | SciQ-2904 | elements, radioactivity
Title: Why radioactive elements emit alpha beta and gamma rays I am confused about this that why radioactive elements emits alpha beta and gamma rays WHILE other elements can't do so. The stability of nuclei is really a sophisticated topic in theoretical quantum mechanics. But there is a simple way to think about what is happening that doesn't get too intense with the quantum mechanical theory.
Nuclei are made from two particles: protons and neutrons. But protons are positively charged and repel each other. The electromagnetic force is very strong and therefore this force is very large. So the first mystery is why all nuclei don't just fly apart.
The reason they don't is that there are two very short-range but very strong forces that bind the nucleus together: the strong and weak nuclear forces. Without getting into mind-bending topics in theoretical physics we can understand something about their net effect like this.
The interaction of the electromagnetic force and the two nuclear forces has some structure (it's quantum stuff, just accept it). Some combinations of protons and neutrons are more stable than others. Each combination has an energy level and some combinations have lower energy than others. Nuclei with even numbers of protons and neutrons are more stable than odd-odd combinations and nuclei with wildly unbalanced neutron to proton ratios are less stable. Neutrons act a little like a glue, helping protons stick together (this is an oversimplification as too many neutrons is also a source of instability: this is a consequence of a complicated interplay of several forces). But bigger nuclei are less stable and need a higher ratio of neutrons. And some large nuclei are just too large for the forces to keep them together so beyond a certain point all nuclei are unstable.
Some nuclei can be transformed into a more stable (lower energy) nucleus by various forms of radioactive decay. Nuclei with too many neutrons can emit a beta particle (this decay mode converts a neutron into a proton); elements with too many protons can emit a positron (converting a proton into a neutron). Bigger nuclei can become more stable by kicking out an alpha particle (which makes the nucleus significantly smaller, moving it towards the stable zone). Gamma radiation is associated with some of these modes: the high energy photons "mop up" the excess energy (I'm simplifying a lot).
The following is multiple choice question (with options) to answer.
What occurs when an unstable nucleus emits an alpha particle and energy? | [
"alpha decay",
"nucleus decay",
"radar decay",
"alpha radition"
] | A | Alpha decay occurs when an unstable nucleus emits an alpha particle and energy. The diagram in Figure below represents alpha decay. An alpha particle contains two protons and two neutrons, giving it a charge of +2. A helium nucleus has two protons and two neutrons, so an alpha particle is represented in nuclear equations by the symbol . The superscript 4 is the mass number (2 protons + 2 neutrons). The subscript 2 is the charge of the particle as well as the number of protons. |
SciQ | SciQ-2905 | molecular-structure, structural-formula
Title: What is the name and formula of this structure? Could anyone please let me know the formula and name of this structure? Any answer is helpful. Could you also summarize how to deduce the formula?
Here is an image: That's Atorvastatin, a cholesterol lowering drug (works by inhibiting the enzyme HMG-CoA reductase).
https://en.wikipedia.org/wiki/Atorvastatin
For more data, see e.g. https://www.trc-canada.com/product-detail/?CatNum=A791725
The following is multiple choice question (with options) to answer.
What molecule can be used by the body to synthesize cholesterol ? | [
"ethylene coa",
"hydroxide coa",
"acetyl coa",
"chloride coa"
] | C | Because of the link between high levels of cholesterol and heart disease, it is commonly seen by the general public as a “bad” molecule. However, cholesterol plays a vital role in the body, as both a structural component of cell membranes and a metabolic precursor to various steroid hormones. Only about 30% of the cholesterol in our bodies comes from our diet; the rest is synthesized in the liver, intestines, adrenal glands, and reproductive organs. The same acetyl CoA molecule that provides biochemical energy can also be used by the body to synthesize cholesterol. There are approximately twenty-two steps involved in the formation of cholesterol from acetyl CoA. |
SciQ | SciQ-2906 | human-genetics
Title: In our 23 chromosome pairs, do the 2 members of the pair have distinct or virtually identical sequences? I understand that we have 46 DNA molecules in the nucleus of our cells, arranged in 23 pairs: 22 autosomal and 1 sex chromosome pairs.
I have read in different sources that the pairs contain nearly identical members, excluding any mutations. I have also read that the pairs contain 1 member we inherited from our mothers and 1 we inherited from our fathers, which are different due to inheritance.
This seems contradictory, given that genealogical companies match up on the differences on these chromosomes.
My understanding was that meiosis creates sperm and egg cells that each carry 23 chromosomes - they are haploids. During the first steps of meiosis that creates the reproductive cells we have a combining of the parent's chromosome pair from their parents to create 4 daughter cells, each independently viable, where the recombination of the chromosome pair has occurred at somewhat predictable spots (for you perhaps :-) ) and that these spots can be related to genes. It is this step that give us our genetic variation between siblings for example. A new person's DNA is partially formed from any one of these highly varied daughter cell possibilities.
Fertilization combines the reproductive cells to produce the 46 chromosome zygote with is again diploid.
I think this understanding supports the second interpretation that our chromosome pairs are not 2 nearly identical DNA molecules but are distinct.
Have I got this right? Is there a missing process or a misunderstanding in my interpretation? Homologous chromosomes (those that are paired up), excluding the sex pair are almost identical in size, shape and genes (members as you called them) present in them.
Genes determine traits and each homologous chromosome controls the same traits. The level of identity of a gene inside a population varies between genes. There are very conserved ones that do not change even between humans and yeast and others that vary alot event inside a species. This changes can be small in sequence length, a simple base (letter) swap or one deletion, and have a huge effect on the traits. This is how chimps and humans are very different but share 98.6% of their genome and humans are very similar and share 99.9% of their genome.
In summary, on the bigger scale homologous chromosomes are very similar (size, shape, traits inside), on the smaller scale homologous chromosomes have small changes that affect greatly.
The following is multiple choice question (with options) to answer.
Full siblings share how many genes with each other? | [
"25%",
"half",
"100%",
"75%"
] | B | |
SciQ | SciQ-2907 | thermodynamics, thermal-conductivity
Indeed, $1kg$ of silver would feel much closer to body temperature than $1kg$ of diamond (that's alot of diamond!) despite diamond having a higher heat capacity.
The following is multiple choice question (with options) to answer.
Which highly valuable substance found in jewelry has a density of about 19 g/cm^3? | [
"gold",
"rubies",
"diamonds",
"silver"
] | A | Samples that are the same size, but have different densities, will have different masses. Gold has a density of about 19 g/cm 3 . Pyrite has a density of only about 5 g/cm 3 . Quartz is even less dense than pyrite, and has a density of 2.7 g/cm 3 . If you picked up a piece of pyrite and a piece of quartz that were the same size, the pyrite would seem almost twice as heavy as the quartz. |
SciQ | SciQ-2908 | human-biology, evolution, reproduction, human-physiology, sexual-reproduction
Hypothesis 1: Profet (1993) hypothesized that shedding the endometrium may be an effective way to get rid of sperm-based pathogens. The accompanying bleeding, Profet hypothesizes, delivers immune cells into the uterine cavity that can combat pathogens.
Hypothesis 2: Strassmann (1996) surmises that the endometrial microvasculature is designed to provide the blood supply to the endometrium and the placenta, and that external bleeding appears to be a side effect of endometrial regression that arises when there is too much blood and other tissue for complete reabsorption. The relatively large blood loss as seen in humans and chimpanzees can be attributed to the large size of the uterus relative to adult female size and to the design of the microvasculature in the uterus wall.
References
- Crawford (ed), Handbook of Evolutionary Psychology: Ideas, Issues, and Applications, Psychology Press (1998)
- Profet, Quarterly Rev Biol (1993); 68(3): 355-86
- Strassmann, Quarterly Rev Biol (1996);71(2): 181-220
The following is multiple choice question (with options) to answer.
Sperm propel themselves through secretions in the uterus and enter what tube? | [
"gaseous",
"uterine",
"ovarian",
"fallopian"
] | D | A day or two after an ovary releases an egg, the egg may unite with a sperm. Sperm are deposited in the vagina during sexual intercourse. They propel themselves through secretions in the uterus and enter a fallopian tube. This is where fertilization normally takes place. |
SciQ | SciQ-2909 | geology, mineralogy
There is an adage amongst some geologists that states "gold is where you find it". There is no altitude preferable for finding gold deposits. It's found in mountains, in deserts, in forests, under salt lakes, even dissolved in the oceans. The oceans contain the largest quantities of gold, but it is uneconomic to extract it from sea water because the concentration are so low.
Biological indicators, such a vegetation may work for some base metals, such as copper, but not necessarily for gold.
Also, gold can occur as a deposit of just gold, but it can also occur in association with other metals in the form of polymetallic deposits which contain gold, silver, copper, lead or zinc, even uranium.
Finally, not all deposits of minerals, gold included, are reserves. To be classified as a reserve and an orebody, a deposit of mineralization must be economic to mine.
The following is multiple choice question (with options) to answer.
What type of minerals are often found where seas once covered the land? | [
"magnesium",
"sea salt",
"carbonate",
"crystals"
] | C | Carbonate minerals are often found where seas once covered the land. Some carbonate minerals are very common. Calcite contains calcium, carbon, and oxygen. Have you ever been in a limestone cave or seen a marble tile? Calcite is in both limestone and marble. Azurite and malachite are also carbonate minerals. They contain copper instead of calcium. They are not as common as calcite. Malachite and azurite are used in jewelry; as you can see, they are very colorful ( Figure below ). |
SciQ | SciQ-2910 | proteins, amino-acids, classification
Title: Classifying Polypeptides (and/or Proteins) Since polypeptides are a linear chain of twenty amino acids, each having a single letter abbreviation (e.g. Alanine = A). So can a polypeptide be represented as just the sequence (say: ADN for an Alanine, Aspartic acid, Asparagine polypeptide)?
This method of classifying polypeptides would lead to a possible 8000 (20**3) variations just for 3-amino-acid-polypetides (3200000 for 5-amino-acid-polypeptides, etc.) and that there would be many variations; and for longer polypeptides - that is, proteins - there would be even more variations.
Or are only the important polypeptides and proteins named, since not every variation of polypeptides and proteins are found in the body? I would've thought that many proteins (and enzymes, etc.) are incredibly specific and so they could be classified in some methodological way, as opposed to just 'lipase' or 'carbohydrase' which provides no structural information (though it would have a long methodological name). You can certainly refer to short peptides by their sequence. I don't know of any exact boundaries, but I've seen tripeptides referred to by either their three letter codes (Ala-Asp-Asn) or even the chemical name (alanylaspartylasparagine) although obviously that gets ridiculous pretty quickly.
As the largest known protein, titin also has the longest IUPAC name of
a protein. The full chemical name of the human canonical form of
titin, which starts methionyl... and ends ...isoleucine, contains
189,819 letters and is sometimes stated to be the longest word in the
English language, or any language. However, lexicographers regard generic names of chemical compounds as verbal formulae rather than English words
The following is multiple choice question (with options) to answer.
How many amino acids generally consist in protien? | [
"67 or more",
"7 or more",
"13 or more",
"100 or more"
] | D | A polypeptide is a sequence of amino acids between ten and one hundred in length. A protein is a peptide that is greater than one hundred amino acids in length. Proteins are very prevalent in living organisms. Hair, skin, nails, muscles, and the hemoglobin in red blood cells are some of the important parts of your body that are made of different proteins. The wide array of chemical and physiological properties of proteins is a function of their amino acid sequences. Since proteins generally consist of one hundred or more amino acids, the number of amino acid sequences that are possible is virtually limitless. |
SciQ | SciQ-2911 | meteorology, snow, radar
Also note that winter precipitation adds an extra complication because the particles are lighter in weight and can thus be blown about more by vertical and horizontal winds. Raindrops (and hail) are quite likely to fall unless extreme updrafts exist because they are heavy. But drizzle, snow, and sleet may be blown around quite a bit. Without a time-intensive dual-Doppler analysis, you cannot know the wind motion in the storm thoroughly, and therefore will have varying results at times.
And finally, the big wrench is unfortunate inherent to how radars work. They measure the percentage of their sent energy that is reflected back to them. That's great because that's directly connected to the diameter of the item falling (to the 6th power). But unfortunately the grand problem is that in a storm, there is a huge variety of drop/flake sizes mixed together at once... such that we can't extract which combination of particle sizes created it (and thus can't calculate volume to actually know the rain/snow amount that falls). It could be like 6 medium size flakes causing the 10 dBZ echo... or 2 large flakes and 10 small flakes... and each combination is a different volume/snow total. (to see the nitty-gritty math details on this, read more here.) So we can never know for sure the exact rain/snow falling using just radar. The good news is we've at least done lots of experiments and come up with some fairly useful best-practice formulas for using the Z-R ratio in different scenarios. Good, but not perfect.
The following is multiple choice question (with options) to answer.
Rain, snow, sleet, and hail are all examples of what? | [
"temperature",
"liquids",
"erosion",
"precipitation"
] | D | |
SciQ | SciQ-2912 | oceanography, geochemistry
Title: Why is NaCl so hyper abundant in the ocean? Why is sodium chloride far and away the most abundant salt dissolved in ocean water? Its two constituent ions do have a very high frequency in the crust of the earth, but they are far from the most common. Chlorine is (according to Wikipedia) the 21st most abundant element, and sodium 6th.
I certainly understand that a combination of their solubility and reasonably high frequency would lead one to expect them to be abundant in sea water, but they are hyper abundant, completely dominating all other salt ions. Iron, for example, is twice as abundant, and potassium only a little less abundant, and fluorine more abundant than chlorine.
Moreover, if the salts are deposited in the ocean through weathering of rocks and deposition via rivers, why does the salinity not simply grow and grow? I understand that some is lost due to tectonic activity, but it seems extraordinarily unlikely that these two forces should be equally balanced, and so we would see a significant change in average salinity over time.
(Please note I am migrating this question from the Chemistry SE at their recommendation.) Fluoride salts tend to be not particularly soluble in water. Chloride salts are. The same goes for salts containing sodium versus those containing calcium. Sodium chloride is ridiculously easy to dissolve.
Regarding your second question, it is geological forces that keep salinity more or less constant. People formerly argued that the Earth can't be more than a few hundred million years old because otherwise the river waters running into the oceans would eventually result in an insanely high salinity. It turns out that the Earth's oceans are young (young compared to the 4.5 billion year age of the Earth). The vast majority of oceanic crust is less than 100 million years old. We see huge salt deposits sprinkled across the world because those are the dried up remnants of former seas and oceans. Salt is also drawn into the Earth at subduction zones, where it combines chemically with basalt.
The following is multiple choice question (with options) to answer.
Where would you find most pollution of ocean water? | [
"trenches",
"midocean",
"poles",
"coastline"
] | D | Ocean water is most polluted along coasts. That’s because pollution usually enters the water from land. Oil spills also pollute ocean water. |
SciQ | SciQ-2913 | quantum-mechanics, water, liquid-state
Title: Quantum description of water It seems that we have quantum description of solid and gas, but there seem to be few quantum models of liquid, with the exception of Liquid Helium or perhaps Fermi Liquid.
For solids, we often study crystal, which is easier due to the lattice symmetry. For gas, particles often interact weakly so it's easy to formulate a non-interacting model. In this sense, I can see why people choose to study these systems first.
But are there any models that make use of quantum mechanics to explore the liquid phase? Perhaps a quantum mechanical description of water.
Maybe we can combine Shrodinger Equation and Navier Stokes equation in some way. Of course Navier Stokes equation itself is already hard enough, so perhaps we need to go to certain limits. Fermi liquid, Luttinger liquid, Bose-Einstein condensate, Superconductivity and similar states of matter are known as quantum fluids or quantum liquids, and there are books written on the subject, see, e.g., Interactions in quantum fluids. The word liquid/fluid is however somewhat ambiguous, as it may mean different (although not mutually exclusive) things:
The following is multiple choice question (with options) to answer.
Water can be a solid, liquid, and what other form? | [
"plasma",
"square",
"gas",
"ooze"
] | C | Water can be a solid, liquid, or a gas. |
SciQ | SciQ-2914 | sexual-reproduction
So when it's not maintained -- when there's no selection pressure on two populations -- inevitably there will be genetic drift that will randomly disrupt this fine-tuned system. If a population of, say, voles is isolated on an island, they will continue to have pressure to be able to interbreed with other voles on the island, but if they can't interbreed with those on the mainland there won't be any consequences, and so over long enough time they'll drift and lose that ability -- just as many apes, not suffering any consequences from not synthesizing vitamin C, gradually lost that ability from random drift.
There's another side to it. Two populations in the same location may be positively selected to not be able to interbreed. Think about two groups of finches, one with small fine beaks that eat tiny seeds deep inside pine cones, and one with heavy beaks that crush and eat thick-shelled nuts. They each do fine, but they can interbreed and produce offspring that have intermediate beaks -- too thick to reach the fine seeds that one parent eats, but too delicate to crush the nuts that the other parent eats. Those intermediate offspring will die off, and both parents will have wasted their resources raising them. Both parents would be better off not breeding with each other, but only breeding with their own kind to produce specialized and efficient offspring. There is now selection pressure on the birds to recognize their own kind (perhaps through songs or mating displays) and ultimately to be inter-sterile, so they never waste resources on the un-fit offspring. There's a gradation of separation over time, in which the different populations become more and more distinct. Eventually, at some arbitrary point, humans start calling them "species", but that's just us, not biology.
"Species" is an important concept, but it's not special in evolution; speciation is just one aspect of natural selection, there's nothing magical about it.
The following is multiple choice question (with options) to answer.
What happens to a species when all of the individuals die out or evolve into a different species? | [
"depletion",
"extinction",
"accumulation",
"selection"
] | B | Species go extinct when all of the individuals die out or evolve into a different species. |
SciQ | SciQ-2915 | newtonian-mechanics, fluid-statics, density, buoyancy
Title: Measure liquids density: hydrometer It is possible to measure liquids density with an hydrometer:
The following is multiple choice question (with options) to answer.
The viscosity of a liquid is a measure of what? | [
"ability to absorb flow",
"resistance to flow",
"adaptability to surroundings",
"resistance to change form"
] | B | When you pour a glass of water, or fill a car with gasoline, you observe that water and gasoline flow freely. But when you pour syrup on pancakes or add oil to a car engine, you note that syrup and motor oil do not flow as readily. The viscosity of a liquid is a measure of its resistance to flow. Water, gasoline, and other liquids that flow freely have a low viscosity. Honey, syrup, motor oil, and other liquids that do not flow freely, like those shown in Figure 10.15, have higher viscosities. We can measure viscosity by measuring the rate at which a metal ball falls through a liquid (the ball falls more slowly through a more viscous liquid) or by measuring the rate at which a liquid flows through a narrow tube (more viscous liquids flow more slowly). |
SciQ | SciQ-2916 | energy, electron-affinity
Title: Why energy is released when an electron is added to a neutral atom? Question :
Why energy is released when an electron is added to a neutral atom?
I read somewhere
“When electrons are added to an atom, the increased negative charge puts stress on the electrons already there, causing energy to be released.”
I didn't understand What is stress and how energy is released due to stress? If the electron statistical distribution around the atomic kernel had been perfectly spherically symmetric, and if the electron occurance distribution had not mutually overlapped, than by the Gauss law of electrostatics, the net force between a neutral atom and an electron would have been zero.
But as neither of above conditions is true, a kernel charge is not fully screened off by electrons, acting as having a residual, "effective charge", what allows releasing energy by bounding an extra electron. See Slater rules.
An extra electron puts among other electrons some extra stress=mutual repulsion, what somewhat decreases this released energy.
As effective kernel charge and electron mutual repulsion ( classical and Pauli ones ) are 2 major factors affecting energies of electron orbitals in multi-electron atoms.
When the former factor is stronger, energy is released by an extra electron bounding, like for fluorine. And vice versa, like for helium.
The following is multiple choice question (with options) to answer.
How is energy expressed when it is released in a chemical reaction? | [
"as a percentage",
"as negative number",
"as a positive number",
"as an equation"
] | B | When energy is released in a chemical reaction or process, that energy is expressed as a negative number. Figure below shows electron affinities in kJ/mol for the main group elements. |
SciQ | SciQ-2917 | cell-biology, terminology
Title: What is the difference between cytosol and cytoplasm? I've generally seen cytosol defined as the solution inside cells minus the organelles, cytoskeleton, etc and cytoplasm as the cytosol plus the organelles, cytoskeleton, etc. This naturally leads to the impression that cytosol is the cytoplasm minus all the solids. The problem here is that there are all sorts of other large molecules in the cells which could be thought of as solid. Are they also part of the cytosol or are they suspended in it? (I.e. are they part of the cytosol or are they non-cytosol components of the cytoplasm?)
Basically, I'm asking if the precise definition of cytosol is just anything in the cell that's not behind an endomembrane (save the exoskeleton) or if the dividing line is something else.
Subquestion: things can get even more terminologically confused because the cytosol is sometimes called the matrix. What the heck is the preferred terminology with this stuff? IMO, the definitive answer to this question is given in a paper by J. S Clegg. He traced the origin of the term cytosol to a book chapter by H. A. Lardy, and confirmed by email that Lardy had indeed coined the term. Their definition of cytosol is as follows:
... that portion of the cell which is found in the supernatant fraction after centrifuging the homogenate at 105 000 x g for 1 hour.
The following is multiple choice question (with options) to answer.
What is the term for a structure within the cytoplasm that performs a specific job in the cell? | [
"nucleolus",
"organelle",
"molecule",
"vacuole"
] | B | Eukaryotic cells also contain other organelles besides the nucleus. An organelle is a structure within the cytoplasm that performs a specific job in the cell. Organelles called mitochondria, for example, provide energy to the cell, and organelles called vacuoles store substances in the cell. Organelles allow eukaryotic cells to carry out more functions than prokaryotic cells can. This allows eukaryotic cells to have greater cell specificity than prokaryotic cells. Ribosomes, the organelle where proteins are made, are the only organelles in prokaryotic cells. |
SciQ | SciQ-2918 | cell-biology, organelle
Title: Univocal identifying of a plant cell We yesterday got our biology-exams back and there's one exercise where I don't agree with my teacher. However, since he is the expert and not me, I need the support of external sources, i.e. experts in order to justify my statement.
Now in the exercise, we first had to identify the parts of a cell (which was shown in form of an image) and then in part b) reason whether it was an animal or plant cell.
I had identified a chloroplast and a vacuole and stated that the only cell with this organelles was the plant cell. My teacher answered that I had missed the fact, that the cell had also a cell wall (which is indeed a difference between plant and animal cells).
My question is
Is the fact that the cell had a cell wall necessary in my argumentation, i.e. are there other cells having chloroplasts and a vacuole without being a plant cell?
Could you provide a source which supports, or doesn't support my statement so that I can show it to my teacher?
Thanks in advance Your teacher is right, chloroplasts and vacuoles are not sufficient to define a plant cell.
Amoeba have both chloroplasts (McFadden et al, PNAS, 1994) and vacuoles (Day, J. Morphology, 1927) but they are not plants - and they do not have a cell wall.
Sea slugs eat algae and can "steal" their plastids and keep them working for weeks/months, effectively becoming photosynthetic animals for a while. This is called kleptoplastidy (Pillet, Mob. Genet. Elements, 2013).
The following is multiple choice question (with options) to answer.
What part of a mature plant cell is responsible for storing substances like water, enzymes, and salts? | [
"large vacuole",
"central vacuole",
"little vacuole",
"second vacuole"
] | B | Most mature plant cells have a large central vacuole . This vacuole can make up as much as 90% of the cell’s volume. The central vacuole has a number of functions, including storing substances such as water, enzymes, and salts. It also helps plant tissues, such as stems and leaves, stay rigid and hold their shape. It even helps give flowers, like the ones in Figure below , their beautiful colors. |
SciQ | SciQ-2919 | genomics, proteomics
Title: Genome and Proteome Due to the dynamism of protein expression, a genome can give rise to different proteomes, but could we say that a proteome comes from different genomes? Yes, different genomes can produce the same proteome.
Imagine a genome that only has a single protein-coding sequence (without splicing isoforms), the rest of the genome is simply regulatory sequences. Whatever those regulatory sequences may be, as long as that single protein is expressed, it'll be the same proteome.
If you consider a single nucleotide difference enough to say two genomes are different, then there are probably quite a lot of different genomes on earth that produce proteomes identical with at least one other genome.
The following is multiple choice question (with options) to answer.
Whereas each cell shares the same genome and dna sequence, each cell does not turn on, or express, the same set of what? | [
"eggs",
"babies",
"balls",
"genes"
] | D | Introduction Each somatic cell in the body generally contains the same DNA. A few exceptions include red blood cells, which contain no DNA in their mature state, and some immune system cells that rearrange their DNA while producing antibodies. In general, however, the genes that determine whether you have green eyes, brown hair, and how fast you metabolize food are the same in the cells in your eyes and your liver, even though these organs function quite differently. If each cell has the same DNA, how is it that cells or organs are different? Why do cells in the eye differ so dramatically from cells in the liver? Whereas each cell shares the same genome and DNA sequence, each cell does not turn on, or express, the same set of genes. Each cell type needs a different set of proteins to perform its function. Therefore, only a small subset of proteins is expressed in a cell. For the proteins to be expressed, the DNA must be transcribed into RNA and the RNA must be translated into protein. In a given cell type, not all genes encoded in the DNA are transcribed into RNA or translated into protein because specific cells in our body have specific functions. Specialized proteins that make up the eye (iris, lens, and cornea) are only expressed in the eye, whereas the specialized proteins in the heart (pacemaker cells, heart muscle, and valves) are only expressed in the heart. At any given time, only a subset of all of the genes encoded by our DNA are expressed and translated into proteins. The expression of specific genes is a highly regulated process with many levels and stages of control. This complexity ensures the proper expression in the proper cell at the proper time. |
SciQ | SciQ-2920 | biophysics, theoretical-biology, ecosystem
Systems ecology, especially with regard to energy and nutrient flow.
This type of ecology can be strongly influenced by physics. For one example see the book Theoretical Ecosystem Ecology: Understanding Element Cycles by Ågren & Bosatta (Ågren was originally a physicist)
Physical limitations to growth and transport
This can include for instance mechanical contraints on plant growth (see e.g. the book Plant Physics by Nicklas & Spatz), water transport in trees (see e.g. this BioSE question) or the biomechanics of movement (see e.g. Hudson et al (2012) on the speed and movement of cheetahs or Wikipedia: Biomechanics).
Allometric relationships between organisms, e.g. with regard to metabolism
To explain these types of relationships knowledge in physics is useful. See e.g. Kleiber's law for more.
MAXENT as a general approach to ecological patterns or to model species distributions
This is basically a tool lifted from physics that can be applied to ecological problems. There are many papers to look at, but Harte & Newman (2014) (Harte is another previous physicist) and Elith et al (2010) are two good starting points.
Dynamical modelling of populations and communities
This field use many of the same tools for analysis as physics, e.g. systems of differential equations. One of the pioneers in this field (among many) were Robert May (also started with a PhD in physics), and his classical book Theoretical Ecology: Principles and Applications is still a good starting point.
Energy harnessing and conversion by organisms
This can refer both to how organsims convert prey to energy (e.g. conversion efficiencies) and the physics of photosynthesis (which is an interesting intersection between physics and molecular biology). See Jang et al (2004) and O'Reilly & Olaya-Castro (2013) for examples of the how quantum mechanics can inform us about photosynthesis.
Hopefully this will give you a sense of some different ways that knowledge in physics can be useful for biology.
The following is multiple choice question (with options) to answer.
In biology, what is required for ecosystems to survive? | [
"helium",
"energy",
"space",
"minerals"
] | B | In biology, energy is required for ecosystems to survive, as all living organisms need energy. Within an organism, energy is needed for growth and development of a biological cell or an organelle within that cell. Energy is also needed for all biochemical reactions within that cell. Therefore, energy is stored within cells in the chemical bonds of substances such as carbohydrates (including sugars), lipids, and proteins. This energy is released during aerobic respiration. |
SciQ | SciQ-2921 | biochemistry, metabolism, bioenergetics
Title: What is the energy source for adipocytes? Since adipocytes export fatty acids and glycerol and don't use them as an energy source, what is the main source of energy for adipocytes? Adipocytes use glucose as an energy source. They express the insulin-responsive glucose transporter GLUT4 just like muscle cells so that when blood glucose levels rise they are primed to take the glucose up for fatty acid biosynthesis, but they also use glucose as a fuel molecule.
The following is multiple choice question (with options) to answer.
Because glucose is a major cellular fuel, starch represents a supply of what? | [
"energy",
"carbon",
"oxygen",
"hydrogen"
] | A | |
SciQ | SciQ-2922 | botany, reproduction
Title: Are the seeds in a single capsicum fruit genetically identical? Hopefully not a too-basic question for the venue. I'm a chile pepper growing hobbyist and have spent some time searching around and reading up on pepper (angiosperm) reproduction, but I'm not getting a clear picture of the details.
It seems like flowers have multiple ovules and it seems like one pollen-grain landing on the stigma leads to fertilization of a single ovule. And it seems like that process produces a single seed.
But that fertilization also prompts fruit growth and flower death and capsicum fruits have many seeds, never just one (that I've ever seen).
So, does each seed have a potentially different father? Or are the multiple seeds generated through a reproductive/cloning process that I'm not seeing written about? Or something else? No, the seeds are not genetically identical. Each seed come from the fertilization of an ovum with a sperm from a separate pollen grain. Since each pollen grain can come from a different plant, the seeds will generally differ from one another.
Additionally, even ova from a single plant will not usually be genetically identical to one another. This is because the process that creates the ova (meiosis) shuffles the genes of the parent plant on then places only half into the ovum. The same kind of shuffling goes on in the creation of pollen grains.
In the chili pepper genus (Capsicum), plants are predominantly self-pollinating. This means the majority of the pollen for the seeds in a fruit will come from the very same plant. This generally reduces the amount of variation seen in the offspring compared to complete cross-plant pollination. Some cross-pollination can nevertheless occur if there are other varieties in the neighborhood. The fruit will not show the effects of the new genetic combinations present in its seed, but only a plant grown from the seed will make the differences evident.
The following is multiple choice question (with options) to answer.
Seed plants that produce seeds in the ovaries of their flowers are known as what? | [
"spores",
"gymnosperms",
"conifers",
"angiosperms"
] | D | Angiosperms are seed plants that produce seeds in the ovaries of flowers. Today, they are by far the most diverse type of seed plants. In fact, the vast majority of all modern plants are angiosperms. There are hundreds of thousands of species of them. The apple tree in Figure below is an example of a common angiosperm. |
SciQ | SciQ-2923 | biochemistry, gas-laws
Title: What is the state of aggregation (gas, liquid) of oxygen in blood? Atmospheric oxygen is in O2 and a gas. Then we inhale the air, our efficient lungs do the magic to filter out the oxygen and push them into the blood stream.
When we say hemo and globin transport the oxygen using the iron ions. In what state oxygen is transported in the blood? as a gas or a liquid or an ion? It is hard for me to conceive of the idea that oxygen would be in gaseous form in the blood. "GAS in blood?" e.g. Arterial Blood Gas Test
Also, how does the lungs convert the gas into something that is compatible to be in blood?
References:
Amount of Oxygen in the Blood Regarding the state of oxygen in blood: It is in solution in the blood plasma (which mostly consists of water), in the form of single molecules. Think of water which you leave exposed to air: carbon dioxide will be captured and dissolved (along with the other gases in air), but these molecules are not gaseous or liquid, but rather "in solution", which is different from the "classical" states.
Back to oxygen: As your reference already states, most of the oxygen in solution will bind to hemoglobin. The actual state of oxygen in that complex has been debated, but it is believed to be reduced by the hemoglobin iron to the superoxide anion, coordinated to Fe$^{3+}$. See Wikipedia on this.
Also, the lungs do not "convert" the atmospheric oxygen to anything, they rather allow, due to their very large surface area, the quick exchange of oxygen/carbon dioxide in solution and in the air.
The following is multiple choice question (with options) to answer.
Which blood vessels is oxygen transferred through? | [
"cilia",
"capillaries",
"arteries",
"veins"
] | B | Of the 23 pairs of human chromosomes, 22 pairs are autosomes (numbers 1–22 in Figure above ). Autosomes are chromosomes that contain genes for characteristics that are unrelated to sex. These chromosomes are the same in males and females. The great majority of human genes are located on autosomes. At the link below, you can click on any human chromosome to see which traits its genes control. http://www. ornl. gov/sci/techresources/Human_Genome/posters/chromosome/chooser. shtml. |
SciQ | SciQ-2924 | human-anatomy
Title: Why is a penis an organ? According to Wikipedia an "An organ is a group of tissues with similar functions". I don't know anything about anatomy but it doesn't seem to me that a penis can be delimited somewhere to form a "group". Therefore I do not understand why a penis is considered an organ.
Can you explain it to me ? Frankly, that's a terrible definition by Wikipedia.
Merriam-Webster defines an organ as:
a differentiated structure (such as a heart, kidney, leaf, or stem) consisting of cells and tissues and performing some specific function in an organism
or
bodily parts performing a function or cooperating in an activity
The important defining feature of an organ is not that the tissues have similar functions but that, together, the tissues comprise a functional whole that achieves some end goal.
For the penis, it consists of multiple tissues with different functions:
(from https://www.ncbi.nlm.nih.gov/books/NBK525966/figure/article-20668.image.f1/ - original from Gray's Anatomy)
The different tissues pictured here: the fibrous envelope, the corpora cavernosa, the septum pectiniforme, the urethra and blood vessels, the nervous tissue in the skin: all of these tissues have different individual functions: structural, erectile, carrying urine or semen, etc.
The key that unifies them into an organ is that the functions of the penis at the organism level (principally sexual function) are not served by any of these tissues alone, but rather by their combination in a full structure: an organ.
Ultimately, organ definitions are somewhat opinion-based: people are lumpers and splitters, so you might find conflicting definitions for which groupings of tissues reflect distinct organs, but I think by most standards you would find the penis to be considered a distinct organ, affiliated with but distinct from the primary sex organs and associated glands.
The following is multiple choice question (with options) to answer.
What small biological structures make up all living things, including the human body? | [
"scales",
"cells",
"proteins",
"lipids"
] | B | Cells make up all living things, including your own body. This picture shows a typical group of cells. But not all cells look alike. Cells can differ in shape and sizes. And the different shapes usually means different functions. |
SciQ | SciQ-2925 | meteorology, atmosphere, carbon, co2, rain
Bear in mind that this assumes an enormous rainfall intensity, 100% CO2 saturation of the water and equilibrium chemical dynamics. After the raindrops hit the ground at least half of it will immediately re-evaporate back into the air, leaving, at absolute most, about 3% of the atmospheric CO2 leached out of the atmosphere that will be available to react with the soil, rock or biosphere. Also consider that this is but one of several important processes affecting CO2 transience, such as photosynthesis, respiration, volcanism, industrial pollution, etc. So the CO2 estimates that you read about are average values. Advection and turbulent air mixing should ensure that the CO2 regains approximately normal concentration within an hour or two after rainfall.
The following is multiple choice question (with options) to answer.
How does carbon dioxide chemically weather rocks? | [
"by creating water",
"by creating acids",
"by creating proteins",
"by creating heat"
] | B | Carbon dioxide chemically weathers rock by creating acids. |
SciQ | SciQ-2926 | waves, popular-science, particle-physics, wave-particle-duality
This is known as wave-particle duality.
As I said at the beginning, waves and particles are the same thing. There are some "waves" like electromagnetic waves which make particles move. These are only called "waves" because it is easier to model and calculate that way. It is possible to describe the interaction as 2 (or more) particles (but it is considerably more difficult).
I hope this answers your question.
The following is multiple choice question (with options) to answer.
What is the interaction of waves with other waves called? | [
"wave mixing",
"wave induction",
"wave dancing",
"wave interference"
] | D | When two or more waves meet, they interact with each other. The interaction of waves with other waves is called wave interference . Wave interference may occur when two waves that are traveling in opposite directions meet. The two waves pass through each other, and this affects their amplitude. Amplitude is the maximum distance the particles of the medium move from their resting positions when a wave passes through. How amplitude is affected by wave interference depends on the type of interference. Interference can be constructive or destructive. |
SciQ | SciQ-2927 | chemistry-in-fiction, geochemistry
Title: Which crystals can exist permanently (and do not break down) under normal earth like outside conditions? Hi I am looking for crystals I can use in the world of my novel but I have no idea what types to use or what there are.
So my question is what kind of crystals fit these criteria:
They must be able to exist “permanently” without breaking down in normal earth conditions/atmosphere.
They must be able to grow quite large. (I’m thinking about large hexagonal crystal columns)
I would be very happy if you could list any crystals you know that fist the criteria. With the name I should be able to research further myself and narrow it down.
Thanks in advance.
-
P.s. some of you might have some feeling of déjà vu reading my question as I asked a similar question before but that one was marked as to brought so I am asking it again but trimmed down.
link: How do i create a significantly correct world with large crystal formations in my novel?
P.p.s. if this question is to brought as well please leave a comment explaining how I can make it better because I otherwise really have no idea how to fix it. Quartz (silicon dioxide) sounds like a good bet. It is inert, safe to be around, and insoluble in water. Some examples of naturally occurring quartz crystals are really huge - visit the National Museum of Natural History if you are near DC - or any other natural history museum near you. There you will likely see many other naturally occurring minerals of defined chemical composition that form large crystals. Or go online and look for pictures.
The following is multiple choice question (with options) to answer.
What kinds of rocks can change and become new types of rocks? | [
"any types of rocks",
"igneous rocks",
"sedimentary rocks",
"metamorphic rocks"
] | A | Any type of rock can change and become a new type of rock. Magma can cool and crystallize. Existing rocks can be weathered and eroded to form sediments. Rock can change by heat or pressure deep in Earth's crust. There are three main processes that can change rock:. |
SciQ | SciQ-2928 | seismology, earthquakes, plate-tectonics
Title: Fault representation In most illustrations and diagrams of the types of faults, there is always something similar. I noticed that there is a side of the hanging wall and foot wall which is slanted.
We're supposed to make a models for each type of fault; however, the material to be used will be difficult to cut diagonally. I'd like to know if it is necessary to have one side slanted? Or if having it vertical fine.
Please mention sources too. Thank you. Faults are results of stress. The direction of the stress controls what kind of fault that is formed. The most fundamental reason for a fault to occur is horizontal compression or extension, even if it's often more complicated in reality.
Your two examples are dip-slip faults, with a vertical displacement as a result of horizontal stress.
In your first example, the normal fault. The total distance (from left to right) is increased. There has been an extension of the crust. If the fault plane would have been vertical, no distance would have been gained.
In the second example, the reverse fault, the distance is decreased. It's been a horizontal compression of the crust. The dip of a reverse fault is usually rather steep. If the dip is lower, you'll rather form a ramp. Typical for thrust faults.
Vertical fault planes are associated with strike-slip faults or ring faults above collapsing calderas or sinkholes. It's also common, but not for textbook examples of dip-slip faults.
So, unless you are showing a strike-slip fault, you have to find a way to cut diagonally. Do measure the horizontal displacement!
Addition about making fault models:
We made a layer cake for a college some time ago and (of course) wanted to have a fault in it. The simplest way was to make a reverse fault, erode the uppermost layer of the hanging wall block and assume that the lowest exposed layer was of the same lithology (chocolate sandstone reservoir rock). However, it took some geoenginering to make it look good and we decided to make an impact crater next time.
The following is multiple choice question (with options) to answer.
What type of earthquake has a shallow focus because the plates meet near the surface? | [
"divergent boundary",
"tectonic",
"gas giant",
"transform fault"
] | D | Transform fault earthquakes have shallow focus because the plates meet near the surface. |
SciQ | SciQ-2929 | fluid-dynamics, waves, geophysics
Title: What is the dominant cause for ocean waves at a beach? What is the dominant cause for ocean waves at a beach? Are they the result of wind/pressure difference? If so, the waves do seem to exist in similar intensity even during relative quiet times of the day.
Is there a simple mathematical model that we can quickly explain the intensity/frequency of waves with? Does the strength of the waves (say the variance and mean of the amplitude of waves) relate to a simple physical quantity (temperature, off shore wind, pressure difference)? Yes, primarily wind. It's called the Kelvin-Helmholtz instability. Strong winds in an area will excite a range of wavelengths, the longer wavelengths will go faster according to the deep water dispersion relation ( speed proportional to square root of wavelength). So if you see a train of waves with decreasing wavelength over time, you could in principle infer a common point of origin (this is a common textbook or qualifying exam type problem).
The following is multiple choice question (with options) to answer.
What causes waves to bring sand up onto the beach during summers? | [
"no energy",
"low sand density",
"high energy",
"low energy"
] | D | Waves also move sand from the beaches on shore to bars of sand offshore as the seasons change. In the summer, waves have lower energy so they bring sand up onto the beach. In the winter, higher energy waves bring the sand back offshore. |
SciQ | SciQ-2930 | acid-base, lewis-structure
For sodium hydroxide, one must realize that in an aqueous medium, the two ions will fully dissociate. The hydroxide anion will act as a Lewis base, but the sodium cation with its full outer electron shell will hardly act as an acid.$^3$
The following is multiple choice question (with options) to answer.
What kind of bases completely dissociate in water, releasing all hydroxide anions into the solution? | [
"unusual",
"strong",
"weak",
"whole"
] | B | Strong bases completely dissociate in water, releasing all hydroxide anions into the solution. The most common strong bases are soluble metal hydroxides. Weak bases partially deprotonate water to form small amounts of hydroxide and the protonated base. |
SciQ | SciQ-2931 | homework-and-exercises, electromagnetism, atomic-physics
Title: How to find the magnetic field due to a revolving electron of hydrogen atom in first orbit So, I was thinking about the Bohr model of atom and I started to wonder how we could find the magnetic field due to a revolving electron (produced at the location of proton) of hydrogen atom in first orbit.
Example:- How to find the magnetic field due to a revolving electron of hydrogen atom in first orbit? Given h ~$ 6.625*10^{-24} $;charge of electron~$1.6*10^{-19}$; $pi~ 3.141$; mass of electron~ $9.10*10^{-31}$. If you naively use a Bohr-like model for the hydrogen atom, then the electron in its ground state is imagined as moving in a circular orbit of radius $r$ and moving with a speed $v$. In this case you could argue the electron is moving, moving charge is current, current creates a magnetic field. Following this model you might expect the magnetic field at the centre of the loop. From classical electromagnetism the magnetic field at the centre of a loop of radius $r$ carrying a current $I$ is $B = \frac{\mu_0 I}{2 r}$.
The question now becomes what do you use for the current. You're aware that the electron isn't a continuous charge distribution so that you have to use the following definition of current, namely current is the rate of change of charge passing you $I = \frac{\Delta Q}{\Delta t}$. Now, if the electron is moving fast enough in it's orbit you can imagine it to be roughly "smeared out" along its path. The electron takes an amount of time $\Delta t$ to move all the way round the orbit of length $2 \pi r$ and since its speed is $v$, this gives $\Delta t = \frac{2 \pi r}{v}$ and the appropriate current to use as $I = \frac{ev}{2 \pi r}$. Plugging this in gives $$B = \frac{\mu_0 e v}{4 \pi r^2}.$$
The following is multiple choice question (with options) to answer.
What model of the atom features an electron orbiting a nucleus, forming a closed-current loop and producing a magnetic field with a north pole and a south pole?. | [
"hydrogen model",
"planetary model",
"gravitational model",
"solar model"
] | B | Figure 22.13 (a) In the planetary model of the atom, an electron orbits a nucleus, forming a closed-current loop and producing a magnetic field with a north pole and a south pole. (b) Electrons have spin and can be crudely pictured as rotating charge, forming a current that produces a magnetic field with a north pole and a south pole. Neither the planetary model nor the image of a spinning electron is completely consistent with modern physics. However, they do provide a useful way of understanding phenomena. |
SciQ | SciQ-2932 | entomology, pathology, parasitology
Title: Why is the species-diversity of deadly parasites greatest in the tropics? There are so many parasites living in tropical regions of Africa, South America, or Asia, but very few in Europe or North America.
Is this due to climate, or are there other reasons?
Many of the tropical diseases and parasites are transmitted by insects, such as flies and mosquitoes. Well there are flies and mosquitoes in Europe as well.
There might be malaria-transmitting mosquitoes in the very south of Europe, and there is encephalitis transmitted by ticks. But that's it. Why don't the hundreds of different parasitic species from Africa spread to Europe ? The diversity of parasites shows a gradient with increasing diversity from the poles to the equator. Several reasons have been brought forth to explain the latitude-dependency of parasite diversity:
An increased diversity overall around the equator; species diversity in general is greater in the rain forests and hence more hosts are available and thus more parasitic species can develop that target specific hosts;
Larger amounts of precipitation and higher temperatures around the equator may favor the development and transmission of parasites (Nunn et al., 2005);
Increased available energy overall around the equator (Guernier et al., 2004).
References
- Guernier et al., PLOSone (2004): 0020141
- Nunn et al., Diversity and Distrib (2005); 11: 249–56
The following is multiple choice question (with options) to answer.
Nearly all apicomplexans are parasites of what? | [
"animals",
"stars",
"plants",
"fungi"
] | A | |
SciQ | SciQ-2933 | cell-biology
Title: Structure of Cell Are cells spheres or ovals/circles bound by phospholipidbilayer?
If they are spherical how are we able to see the nucleus through the phospholipid bilayer under a microscope? Not exactly. That is a stereotype of cells. Muscle cells are not round nor oval, but rather elongated rods. If you were to look up epithelia cells, you can quickly see that cells are grouped based on their physical characteristics; simple (round/oval & single layer), columnar, and cuboidal to name a few. Cells come in many shapes and sizes. As Hans stated, stains are vital in viewing cellular components. There is a diverse amount of stains used - which all carry a purpose and benefit in a specific application.
The following is multiple choice question (with options) to answer.
What is the term for sheets of cells that form a boundary between a mass of cells and a cavity or space? | [
"myelin",
"ganglion",
"epithelia",
"mucus"
] | C | Tight junctions are common at epithelia, which are sheets of cells that form a boundary between a mass of cells and a cavity or space (a lumen ). The membranes of these cells join together, forming a virtually impermeable barrier to fluid. Tight junctions essentially seal adjacent epithelial cells in a narrow layer just beneath their apical surface, which is the portion of the cell exposed to the lumen. The rest of the cell surface is known as the basolateral surface. Tight junctions prevent integral membrane proteins from moving between the apical and basolateral surface, maintaining the properties of those distinct surfaces. For example, receptor-mediated endocytosis occurs at the apical surface and exocytosis at the basolateral surface. |
SciQ | SciQ-2934 | cancer, mutations
Here is another great paper that specifically addresses your question, linking increased cell division with the accumulation of both significant and insignificant mutations, which over time, lead to an accumulation of mutations needed for cancer to develop.
The following is multiple choice question (with options) to answer.
What does a cell need to transform into a cancerous cell? | [
"mutations",
"microbes",
"parasites",
"adaptations"
] | A | Typically, a series of several mutations that constitutively activate oncogenes and inactivate tumor suppressor genes is required to transform a normal cell into a cancer cell ( Figure below ). Cells have developed a number of control mechanisms to overcome mutations in proto-oncogenes. Therefore, a cell needs multiple mutations to transform into a cancerous cell. A mutation in one proto-oncogene would not cause cancer, as the effects of the mutation would be masked by the normal control of the cell cycle and the actions of tumor suppressor genes. Similarly, a mutation in one tumor suppressor gene would not cause cancer either, due to the presence of many "backup" genes that duplicate its functions. It is only when enough proto-oncogenes have mutated into oncogenes and enough tumor suppressor genes have been deactivated that the cancerous transformation can begin. Signals for cell growth overwhelm the signals for growth regulation, and the cell quickly spirals out of control. Often, because many of these genes regulate the processes that prevent most damage to the genes themselves, DNA damage accumulates as one ages. |
SciQ | SciQ-2935 | fluid-dynamics
Title: Are waves affected by an under-water barrier? Given a wave propagating at the surface of still water towards a barrier that is below the surface, but at a distance that is of the order of the dimensions of the wave (such as depicted in the scheme below).
How will the course of the wave be affected ?
Will it be blind to it and pursue its course unaffected ?
Will it only partially pursue and a part of it will bounce back ?
Something else ?
<
wave
/~~~
/~~~~\ ->
~~~~/~~~~~~`~~~~~~~~~~~~~~~~~~~~~~~~ water surface
____
| |
| |
____________________| |__________
barrier Ocean surface waves that are said to 'feel' bottom are known as shallow water waves which are categorically differentiated from deep water waves according to wavelength and depth, and which are not as affected by the depth of the sea floor.
Ocean surface waves are a movement of energy, not a bulk forward motion of water but do result in local circular orbits of the water particles. With depth the circular orbits flatten into elliptical orbits and eventually vanish, and it's at this depth obstacles will no longer influence surface wave motion. For obstacles that do intrude into this space, the circular or elliptical motions are disturbed and energy is dissipated towards the upper water layers, building up wave height. IN very shallow water the build up can get high enough that the wave can no longer sustain its shape and you have a breaking wave.
The property that actually leads to the loss of energy from obstacles is the viscosity of the water, the ability for layers of water to flow over one another.
The following is multiple choice question (with options) to answer.
Circular water waves decrease in what property as they move away from where a rock is dropped? | [
"frequency",
"amplitude",
"mass",
"voltage"
] | B | 16.11 Energy in Waves: Intensity 17. Two identical waves undergo pure constructive interference. Is the resultant intensity twice that of the individual waves? Explain your answer. Circular water waves decrease in amplitude as they move away from where a rock is dropped. Explain why. |
SciQ | SciQ-2936 | homework-and-exercises, pressure, unit-conversion
Restricting our attention to the pressure and height differences only, it's clear that $h=1$ millimetre of mercury corresponds to the pressure difference:
$$ \delta P = h \rho g = 0.001 \,{\rm m} \times 13,595.1\, {\rm kg}/{\rm m}^3 \times 9.80665\,{\rm m}/{\rm sec}^2 = 133.332 \,{\rm Pa} $$
The inverse relationship is 1 Pascal is equivalent to $1/133.332 = 0.0075006$ mmHg. The exact values of the densities are a little bit conventional - the densities depend on temperature and pressure and the gravitational acceleration depends on the place. In the past, 1 mmHg wasn't needed that accurately. In the modern era, we define 1 mmHg by your relationship, and 1 Pa is much more accurately defined in terms of "fundamental physics".
The following is multiple choice question (with options) to answer.
What property of certain states of matter can be given in units of millimeters of mercury? | [
"pressure",
"velocity",
"solvency",
"gravity"
] | A | Pressure is given in units of millimeters of mercury. We can either convert this to atmospheres or use the value of the ideal gas constant that includes the mmHg unit. We will take the second option. Substituting into the ideal gas law,. |
SciQ | SciQ-2937 | energy
Title: Why are more energetic events less likely So I was watching this very interesting video by DoS and noticed all the downward sloping lines in his Doomsday graph, and started wondering what is the fundamental reason behind those expected trends. I mean, it seems obvious that bigger hurricanes are rarer than smaller ones but I couldn't quite point out what law of physics/postulate implies this. Is it entropy, the second law in some way? Or just because we assume the energy in a semi-isolated system if finite therefore more energetic events are necessarily less common? But that doesn't really explain other curves for climate change or resistant bacteria. Or even why the volcanoes one is a plateau. I'm not sure if this is even the most appropriate SE to post this on, or if I'm grasping at straws, but I couldn't help getting annoyed that as a physics grad I couldn't explain the shape of those curves by anything else than an intuition. Thanks More energetic events require more energy to get started. The "activation energy" is higher. It is less likely to get that activation energy, hence the events themselves are also less likely.
You might be familiar with plots such as this one, which shows how catalysis works. You might also remember plots of quantum tunneling. The higher the barrier, the less likely it is to tunnel through.
The following is multiple choice question (with options) to answer.
Loss of energy is the reason that what typically has few levels? | [
"humans",
"video games",
"food chain",
"the atmosphere"
] | C | At each level of a food chain, a lot of energy is lost. Only about ten percent of the energy passes to the next level. Where does that energy go? Some energy is given off as heat. Some energy goes into animal wastes. Energy also goes into growing things that another consumer can't eat, like fur. It's because so much energy is lost that most food chains have just a few levels. There’s not enough energy left for higher levels. |
SciQ | SciQ-2938 | evolution, mammals, marine-biology
The question remains: why? The most likely explanation is that cetaceans evolved to exploit an unfilled ecological niche or adapted to new niches that formed as a result of plate tectonics or other types of environmental changes that occurred 50-55 million years ago. The niche describes all of the living and non-living resources needed by an organism to survive. Although land-based mammals were increasing in diversity, few or none were present in the oceans. The basic hypothesis is that the early whale-like artiodactyls, like Indohyus and Pakicetus were land-based (terrestrial) mammals that spent most of their time near the water's edge. Over time, they adapted to the niches in the ocean. Fossils like Ambulcetus and Rodhocetus showed clear evidence of swimming ability, with flattened tails and the enlarged rear feet. In addition, the nostrils shifted from the front of the face to the top of the head, which we recognize as the blowhole.
The shift to the aquatic habitat allowed these species to exploit resources that were not available to land-based mammals, thereby reducing competition for the resources. Reduced competition allows more individuals to survive and reproduce.
Similar scenarios are very likely for other marine mammals, such as seals or manatees. They evolved to take advantage of ecological niches that were not filled by other organisms. This basic concept, evolving to fill available niches, is a common outcome of the evolutionary process.
The of adaptation of cetaceans and other mammals to the oceans may be similar to that of the hippopotamus. Hippos spend most of their time in the water, and they show many adaptations that allow them to live in the aquatic environment. The eyes and nostrils of the hippo are high on the head, which allows them to remain almost entirely submerged but still see and smell, as shown below.
(Hippo photo by Johannes Lunberg, Flickr Creative Commons.)
Hippos feed underwaters, they are heavy enough to walk on the bottom of the river, and the mate and give birth underwater. The young can suckle underwater. Clearly, hippos seem to be another mammal that is "returning to water." Similar types of processes must have occurred in cetaceans for them to adapt to the marine habitat.
The following is multiple choice question (with options) to answer.
Root-like projections anchor adults of what colony-dwelling animals to solid surfaces such as rocks and reefs? | [
"molluscs",
"corals",
"anemones",
"sponges"
] | D | Sponges come in a variety of shapes and sizes. For example, they may be shaped like tubes, fans, cones, or just blobs. They range in diameter from about a centimeter (0.4 inches) to over a meter (3.3 feet). Many species live in colonies that may be quite large. Adult sponges are sessile. This means they are unable to move from place to place. Root-like projections anchor them to solid surfaces such as rocks and reefs. |
SciQ | SciQ-2939 | It should also be clear that $P$ is connected, as I get from anywhere on earth to anywhere else (barring the poles, of course) without going through the poles. In fact, it is path connected. Take any two points in $P$. Then draw paths from either point to the equator, then connect the points on the equator.
-
thank you very much. I understand now. +1 for your answer. – srijan Jun 7 '12 at 6:06
Glad to help. I would strongly encourage you to spend more time trying to visualize the spaces you work with. It is not always easy (or possible), but often there are useful analogs. – copper.hat Jun 7 '12 at 6:13
Thank you very much for valuable comments and answers."Take any two points in P. Then draw.." this line is self contained. Indirectly we can say If A is connected to B(equator) and B is connected to C. then we have path from C. Am i right? – srijan Jun 7 '12 at 6:18
Yes indeed, you are. – copper.hat Jun 7 '12 at 6:24
Sometimes it is really hard to accept one answer when you have more than one answers of equal importance. – srijan Jun 7 '12 at 6:27
The following is multiple choice question (with options) to answer.
We divide up the earth's seas into five what, which are really all interconnected? | [
"oceans",
"lakes",
"ecosystems",
"continents"
] | A | People divide up the seas into five oceans. But they are really all interconnected. Even so, they are all very different. This ocean is near a shore and is obviously in a cold region. It appears to be a good habitat for whales! No matter what, the oceans have a huge influence on the planet, locally and as a whole. |
SciQ | SciQ-2940 | homework, plant-physiology, plant-anatomy
and 'Vascular Plants = Winning! - Crash Course Biology #37'
https://youtu.be/h9oDTMXM7M8?t=373
[5] Osmosis (water compensating solutes) "In Da Club - Membranes & Transport: Crash Course Biology #5"
https://youtu.be/dPKvHrD1eS4?list=PL3EED4C1D684D3ADF&t=148
Ian (and dad <= all errors and approximations are his :) ).
The following is multiple choice question (with options) to answer.
Regulated by guard cells, stomata allow what to enter and exit the plant? | [
"gases",
"nutrients",
"fluid",
"molecules"
] | A | Chapter 30 1 Figure 30.7 A and B. The cortex, pith, and epidermis are made of parenchyma cells. 3 Figure 30.34 B. 4 C 6 C 8 A 10 B 12 A 14 B 16 C 18 B 20 D 22 C 24 C 26 C 27 Lawn grasses and other monocots have an intercalary meristem, which is a region of meristematic tissue at the base of the leaf blade. This is beneficial to the plant because it can continue to grow even when the tip of the plant is removed by grazing or mowing. 29 Stomata allow gases to enter and exit the plant. Guard cells regulate the opening and closing of stomata. If these cells did not function correctly, a plant could not get the carbon dioxide needed for photosynthesis, nor could it release the oxygen produced by photosynthesis. 31 In woody plants, the cork cambium is the outermost lateral meristem; it produces new cells towards the interior, which enables the plant to increase in girth. The cork cambium also produces cork cells towards the exterior, which protect the plant from physical damage while reducing water loss. 33 Annual rings can also indicate the climate conditions that prevailed during each growing season. 35 A tap root system. |
SciQ | SciQ-2941 | physical-chemistry, thermodynamics, equilibrium, precipitation
Title: Why exactly does precipitation occur? In a solution, we have ions floating around but when we have a precipitate, they're arranged as they would be in a solid. This conversion should cause a decrement in the entropy of the system and cause the reaction to be non-spontaneous, but that is not the case. Data of several $K_\mathrm{sp}$'s suggests that the reactions are very spontaneous, with $\log{K_\mathrm{eq}}$ around $30-40$ for some salts. Why does this happen?
One possible explanation I could think of was that all precipitation processes are enthalpy driven instead of entropy driven but in those cases enthalpy should either be really high and all solubilities must increase upon increase in temperature. I haven't studied these enough to know if that is the case or not, so help from someone more experienced would be appreciated. Short story
Maybe it will help to think first about a ridiculous case. Say you have a large hydrophilic solid, and a small drop of water is added on top. We would not expect the entire solid to disappear into the liquid. Yes, there will be some adsorption and solubility here, yet most of the solid will remain undisturbed. In some sense, the solid 'does not fit' into the liquid droplet over a certain limit.
Similar things are true, again in a certain interpretation, for more realistic situations. What does this 'fitting' mean exactly? It definitely does not mean there is not enough physical space per se. Instead as you increase the concentration of your solute, the distances between solute entities starts to decrease on average. Hence, at a certain radii the intermolecular forces become strong enough to pull the solutes together. There is often some energy barrier to this approaching, as colloid chemists will tell you, but if the end result is some energy minimum, the process will occur at some rate.
The following is multiple choice question (with options) to answer.
The rising and sinking of these can cause precipitation? | [
"temporary air currents",
"underwater currents",
"circular air currents",
"global air currents"
] | D | Global air currents affect precipitation. How they affect it varies with latitude ( Figure below ). Where air rises, it cools and there is precipitation. Where air sinks, it warms and causes evaporation. These patterns are part of the global wind belts. |
SciQ | SciQ-2942 | electromagnetism, polarization, earth
Title: Is reversal of magnetic polarity in a planet an instantaneous occurence? Just what the title states -
Does reversal of magnetic poles in a planet refer to the point in time when reversal is complete?
OR
Does it refer to the entire drawn out process (assuming the poles flip gradually from 0 through 180 degrees? As far as I know the term "reversal of magnetic poles" doesn't have a strict definition, so I suppose different commentators might use it in different ways. However I suspect most of us would use it to describe the whole process.
You describe the process as "drawn out" but no-one knows how long it takes because the dynamics of the Earth's core are poorly understood. On a geological timescale the process looks instantaneous, but then geological timescales are pretty long. Models suggest it could be pretty quick, though how realistic the liquid sodium models are is open to debate.
The following is multiple choice question (with options) to answer.
Where does evidence that magnetic reversals occur come from? | [
"air",
"rocks on ocean floor",
"Volcanoes",
"snow"
] | B | Scientists don’t know for certain why magnetic reversals occur, but there is hard evidence that they have for hundreds of millions of years. The evidence comes from rocks on the ocean floor. Look at Figure below . They show the same ridge on the ocean floor during different periods of time. |
SciQ | SciQ-2943 | experimental-physics, pressure, bernoulli-equation
Title: Differential pressure sensor applications I have two differential sensors and in my experiment I wish to measure the air pressure from below and on top of the ball that is levitated by air. These are my 3 possible setups. Considering the 3 setups what is the best and most accurate way of measuring $P_1$ and $P_2$ ?
Setup A
Utilizes only one differential sensor that measures the dynamic pressure from above the ball and below the ball.
Setup B
Utilizes two differential sensors and a Pitot tube to measure static and dynamic pressure and get its difference.
Setup C
Utilizes two differential sensors, with a similar concept as that of a pitot tube and gets the difference between the dynamic and static pressure from the top and below the ball. Use setup "A" to measure differential pressure. Any drift in each pressure measurement will not be seen if you use one differential pressure cell, but any drift WILL be seen, and will be unpredictable, if you use two separate differential pressure cells to take your readings. Note - setup "A" is very commonly used in industry, where a LOT of differential pressure readings are taken every day (e.g., millions of readings).
If you also need a static pressure reading at the same time that you are getting a differential pressure reading, use a separate pressure measuring device to get that reading.
The following is multiple choice question (with options) to answer.
What is used to measure air pressure? | [
"barometer",
"metrometer",
"thermometer",
"indicator"
] | A |
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