questions stringlengths 37 1.22k | reasoning stringlengths 0 3.56k ⌀ | answers stringlengths 4 138 |
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Obligate anaerobes live and grow in the absence of what?
Here are the choices:
A. atomic oxygen
B. molecular nitrogen
C. molecular carbon
D. molecular oxygen | Visit this site (http://openstaxcollege. org/l/fermentation2) to see anaerobic cellular respiration in action. Other fermentation methods occur in bacteria. Many prokaryotes are facultatively anaerobic. This means that they can switch between aerobic respiration and fermentation, depending on the availability of oxygen. Certain prokaryotes, like Clostridia bacteria, are obligate anaerobes. Obligate anaerobes live and grow in the absence of molecular oxygen. Oxygen is a poison to these microorganisms and kills them upon exposure. It should be noted that all forms of fermentation, except lactic acid fermentation, produce gas. The production of particular types of gas is used as an indicator of the fermentation of specific carbohydrates, which plays a role in the laboratory identification of the bacteria. The various methods of fermentation are used by different organisms to ensure an adequate supply of NAD+ for the sixth step in glycolysis. Without these pathways, that step would not occur, and no ATP would be harvested from the breakdown of glucose. | D: molecular oxygen. |
What is the common term for single-celled fungi?
Here are the choices:
A. yeasts
B. sponges
C. prokaryotes
D. mushrooms | Most fungi are multicellular, but some exist as single cells. Single-celled fungi are known as yeasts. Fungi spend most of their life cycle in the haploid state. They form diploid cells only during sexual reproduction. Like the cells of protists and plants, the cells of fungi have cell walls. But fungi are unique in having cell walls made of chitin instead of cellulose. Chitin is a tough carbohydrate that also makes up the exoskeleton (outer skeleton) of insects and related organisms. | A: yeasts. |
What process allows particles too large to move along the stream bed?
Here are the choices:
A. impaction
B. saltation
C. channelization
D. diffusion | Particles that are too large to be suspended move along the stream bed by saltation. | B: saltation. |
Conducting wires have a small degree of what?
Here are the choices:
A. electrical resistance
B. insulation
C. magnetism
D. heat | Conducting wires have a small electrical resistance. The electrical resistance of a conducting wire is related to the type of metal used and inversely related to the cross-sectional area of the wire. The larger the diameter of a wire, the greater the cross-sectional area, and the lower the electrical resistance will be. When electrons flow through a wire, they repel each other and interfere with the passage of other electrons. If there are a very large number of electrons passing through a wire with small diameter, the electrons will experience a greater resistance than if the wire diameter were larger and the electrons had more space between them. | A: electrical resistance. |
What allowed life to expand and diversify during the early cambrian period?
Here are the choices:
A. cool, dry climate
B. warm, humid climate
C. hot, dry climate
D. cool, humid climate | The warm, humid climate of the early Cambrian allowed life to expand and diversify. This brought the Cambrian Explosion. Life exploded both in diversity and in quantity!. | B: warm, humid climate. |
What do you call the fast-moving air currents high in the troposphere?
Here are the choices:
A. wind streams
B. cyclones
C. stationary fronts
D. jet streams | Jet streams are fast-moving air currents high in the troposphere. They are also the result of unequal heating of the atmosphere. Jet streams circle the planet, mainly from west to east. The strongest jet streams are the polar jets. PIctured below is the northern polar jet ( Figure below ). | D: jet streams. |
What describes a close and long-term interaction between different species?
Here are the choices:
A. dermatitis
B. endosymbiosis
C. symbiosis
D. parasitic | Symbiosis describes a close and long-term interaction between different species. | C: symbiosis. |
Rudolf virchow developed the hypothesis that cells only come from other cells in what year?
Here are the choices:
A. 1898
B. 1848
C. 1858
D. 1868 | In 1858, after using microscopes much better than Hooke’s first microscope, Rudolf Virchow developed the hypothesis that cells only come from other cells. For example, bacteria, which are single-celled organisms, divide in half (after they grow some) to make new bacteria. In the same way, your body makes new cells by dividing the cells you already have. In all cases, cells only come from cells that have existed before. This idea led to the development of one of the most important theories in biology, the cell theory . | C: 1858. |
Because they have free electrons, metals are able to conduct what?
Here are the choices:
A. radiation
B. electricity
C. sound
D. light | Metals can conduct electricity because they have free electrons. | B: electricity. |
What are oil in folded layers of rock called?
Here are the choices:
A. dendrites
B. macroparticle
C. oscillations
D. anticlines | Geologists look for oil in folded layers of rock called anticlines ( Figure below ). Oil moves through permeable rock and is trapped by the impermeable cap rock. | D: anticlines. |
Lymph vessels are like blood vessels, except they move what instead of blood?
Here are the choices:
A. sperm
B. air
C. marrow
D. lymph | Lymph vessels make up a circulatory system that is similar to the cardiovascular system, which you can read about in a previous concept. Lymph vessels are like blood vessels, except they move lymph instead of blood. Lymph is a yellowish liquid that leaks out of tiny blood vessels into spaces between cells in tissues. Where there is more inflammation, there is usually more lymph in tissues. This lymph may contain many pathogens. | D: lymph. |
During the first several weeks of development, the cells of the endometrium nourish what?
Here are the choices:
A. uterus
B. embryo
C. nucleus
D. egg | Development of the Placenta During the first several weeks of development, the cells of the endometrium—referred to as decidual cells—nourish the nascent embryo. During prenatal weeks 4–12, the developing placenta gradually takes over the role of feeding the embryo, and the decidual cells are no longer needed. The mature placenta is composed of tissues derived from the embryo, as well as maternal tissues of the endometrium. The placenta connects to the conceptus via the umbilical cord, which carries deoxygenated blood and wastes from the fetus through two umbilical arteries; nutrients and oxygen are carried from the mother to the fetus through the single umbilical vein. The umbilical cord is surrounded by the amnion, and the spaces within the cord around the blood vessels are filled with Wharton’s jelly, a mucous connective tissue. The maternal portion of the placenta develops from the deepest layer of the endometrium, the decidua basalis. To form the embryonic portion of the placenta, the syncytiotrophoblast and the underlying cells of the trophoblast (cytotrophoblast cells) begin to proliferate along with a layer of extraembryonic mesoderm cells. These form the chorionic membrane, which envelops the entire conceptus as the chorion. The chorionic membrane forms finger-like structures called chorionic villi that burrow into the endometrium like tree roots, making up the fetal portion of the placenta. The cytotrophoblast cells perforate the chorionic villi, burrow farther into the endometrium, and remodel maternal blood vessels to augment maternal blood flow surrounding the villi. Meanwhile, fetal mesenchymal cells derived from the mesoderm fill the villi and differentiate into blood vessels, including the three umbilical blood vessels that connect the embryo to the developing placenta (Figure 28.11). | B: embryo. |
Which type of joints do not allow any movement of the bones?
Here are the choices:
A. fitted
B. linked
C. attached
D. fixed | The skull has fixed joints. Fixed joints do not allow any movement of the bones, which protects the brain from injury. | D: fixed. |
What type of waves carry energy through matter or space as vibrating electric and magnetic fields?
Here are the choices:
A. mechanical waves
B. light waves
C. electromagnetic waves
D. sound waves | Electromagnetic waves are waves that carry energy through matter or space as vibrating electric and magnetic fields. Electromagnetic waves have a wide range of wavelengths and frequencies. Sunlight contains the complete range of wavelengths of electromagnetic waves, which is called the electromagnetic spectrum. The Figure below shows all the waves in the spectrum. | C: electromagnetic waves. |
What happens when water is removed from the endospore?
Here are the choices:
A. its metabolism halts
B. reversal
C. hibernation
D. suspension | A: its metabolism halts. | |
What is the term for the intentional release or spread of agents of disease?
Here are the choices:
A. bioterrorism
B. diversion
C. plague
D. pandemic | Bioterrorism is the intentional release or spread of agents of disease. | A: bioterrorism. |
Two important types of waves include longitudinal waves and what other kind?
Here are the choices:
A. transverse
B. irregular
C. phenomena
D. slow | Like transverse waves, longitudinal waves are mechanical waves, which means they transfer energy through a medium. Unlike transverse waves, longitudinal waves cause the particles of medium to move parallel to the direction of the wave. They are most common in springs, where they are caused by the pushing an pulling of the spring. Although the surface waves on water are transverse waves, fluids (liquids, gases, and plasmas) usually transmit longitudinal waves. | A: transverse. |
The motion of stars in galaxies imply that there is about 10 times as much what as in the luminous objects we can see?
Here are the choices:
A. light
B. density
C. mass
D. heat | Figure 6.18 The diagram shows angular momentum for a circular motion. | C: mass. |
Polymers, ceramics, adhesives, coatings, and liquid crystals are examples of materials recently discovered or developed by what type of scientists?
Here are the choices:
A. geologists
B. chemists
C. engineers
D. material scientists | Chemists are involved in the design and production of new materials. Some of the materials that chemists have helped discover or develop in recent years include polymers, ceramics, adhesives, coatings, and liquid crystals. Liquid crystals are used in electronic displays, as in watches and calculators. The silicon-based computer chip has revolutionized modern society and chemists have played a key role in their design and continued improvement. The calculator shown below uses both a liquid crystal display and chips inside the device. | B: chemists. |
What does the urethra do?
Here are the choices:
A. stores sperm and urine
B. makes sperm and evacuates bowels
C. filters urine and makes sperm
D. carries urine and sperm out of the body | The penis is an external, cylinder-shaped organ that contains the urethra. The urethra is the tube that carries urine out of the body. It also carries sperm out of the body. | D: carries urine and sperm out of the body. |
What is the term used to measure the intensity of sound waves?
Here are the choices:
A. decibel
B. phon
C. amplitude
D. hertz | Loudness refers to how loud or soft a sound seems to a listener. The loudness of sound is determined, in turn, by the intensity, or amount of energy, in sound waves. The unit of intensity is the decibel (dB). | A: decibel. |
What can be thought of as the most biologically productive regions on earth?
Here are the choices:
A. estuaries
B. swamps
C. forests
D. coasts | An estuary is a partly enclosed coastal body of water with one or more rivers or streams flowing into it, and with a free connection to the ocean. Estuaries can be thought of as the most biologically productive regions on Earth, with very high biodiversity. Estuaries are zones where land and sea come together, and where fresh and salt water meet. | A: estuaries. |
What is the scientific term for farsightedness?
Here are the choices:
A. hyperopia
B. myopia
C. hypoxia
D. micropsia | Hyperopia is commonly called farsightedness. People with hyperopia can see distant objects clearly, but nearby objects appear blurry. Hyperopia occurs when images focus in back of the retina because the eyeball is too short. This vision problem can be corrected with convex lenses, which curve outward. The lenses focus images correctly on the retina. | A: hyperopia. |
During fetal development of the heart, what does the bulbus cordis develop into?
Here are the choices:
A. right ventricle
B. right atrium
C. last ventricle
D. left atrium | Following ventricular repolarization, the ventricles begin to relax, and pressure within the ventricles drops. When the pressure falls below that of the atria, blood moves from the atria into the ventricles, opening the atrioventricular valves and marking one complete heart cycle. 35 Afterload represents the resistance within the arteries to the flow of blood ejected from the ventricles. If uncompensated, if afterload increases, flow will decrease. In order for the heart to maintain adequate flow to overcome increasing afterload, it must pump more forcefully. This is one of the negative consequences of high blood pressure or hypertension. 37 After fusion of the two endocardial tubes into the single primitive heart, five regions quickly become visible. From the head, these are the truncus arteriosus, bulbus cordis, primitive ventricle, primitive atrium, and sinus venosus. Contractions propel the blood from the sinus venosus to the truncus arteriosus. About day 23, the heart begins to form an S-shaped structure within the pericardium. The bulbus cordis develops into the right ventricle, whereas the primitive ventricle becomes the left ventricle. The interventricular septum separating these begins to form about day 28. The atrioventricular valves form between weeks five to eight. At this point, the heart ventricles resemble the adult structure. | A: right ventricle. |
A more crucial use of rc circuits for timing purposes is in the artificial pacemaker, used to control what?
Here are the choices:
A. blood pressure
B. heart rate
C. iron levels
D. breathing rate | A more crucial use of RC circuits for timing purposes is in the artificial pacemaker, used to control heart rate. The heart rate is normally controlled by electrical signals generated by the sino-atrial (SA) node, which is on the wall of the right atrium chamber. This causes the muscles to contract and pump blood. Sometimes the heart rhythm is abnormal and the heartbeat is too high or too low. The artificial pacemaker is inserted near the heart to provide electrical signals to the heart when needed with the appropriate time constant. Pacemakers have sensors that detect body motion and breathing to increase the heart rate during exercise to meet the body’s increased needs for blood and oxygen. | B: heart rate. |
What causes earthquakes at mid-ocean ridges to be small and shallow?
Here are the choices:
A. plates are thick , young , and cold
B. plates are thick , old , and hot
C. plates are thin , young , and hot
D. plates are thin , young , and cold | Earthquakes also occur at divergent plate boundaries. At mid-ocean ridges, these earthquakes tend to be small and shallow focus because the plates are thin, young, and hot. Earthquakes in the oceans are usually far from land, so they have little effect on peoples’ lives. On land, where continents are rifting apart, earthquakes are larger and stronger. | C: plates are thin , young , and hot. |
Most geological activity takes place where?
Here are the choices:
A. ocean floor
B. high altitudes
C. center of plates
D. at plate boundaries | Most geological activity takes place at plate boundaries. But some activity does not. Much of this intraplate activity is found at hot spots. Hotspot volcanoes form as plumes of hot magma rise from deep in the mantle. | D: at plate boundaries. |
What do we call the amount of time it will take for half of the radioactive material to decay?
Here are the choices:
A. one full-life
B. one partial-life
C. one quarter-life
D. one half-life | The measure of how quickly a nucleus decays is given by the half-life of the nucleus. One half-life is the amount of time it will take for half of the radioactive material to decay. | D: one half-life. |
What are organisms that depend on other living things for food?
Here are the choices:
A. consumers
B. products
C. customers
D. buyers | Consumers are organisms that depend on other living things for food. They take in organic compounds by eating or absorbing other living things. Consumers include all animals and fungi. They also include some bacteria and protists. | A: consumers. |
Which part of the nerve cell helps transmit nerve impulses?
Here are the choices:
A. cell walls
B. dendrites
C. synapses
D. long, threadlike extensions | Note that like most other cells, these nerve cells have a nucleus. They also have other organelles. However, the long, threadlike extensions of the nerve cells are unique. This is where the nerve impulses are transmitted. | D: long, threadlike extensions. |
Mount kilimanjaro has ________ climates at the top and bottom?
Here are the choices:
A. different
B. similar
C. rainy
D. dangerous | Mount Kilimanjaro has very different climates at the top and bottom. | A: different. |
What physical process occurs when large chunks of food are broken down into smaller pieces?
Here are the choices:
A. swallowing
B. mechanical digestion
C. peristalsis
D. chemical digestion | Mechanical digestion occurs when large chunks of food are broken down into smaller pieces. This is a physical process that happens mainly in the mouth and stomach. | B: mechanical digestion. |
What is the term for the early growth and development of a plant embryo inside a seed?
Here are the choices:
A. fertilization
B. rumination
C. germination
D. secretion | A seed is a reproductive structure that contains an embryo and a food supply, called endosperm. Both the embryo and endosperm are enclosed within a tough outer coating, called a hull (or shell). You can see these parts of a seed in Figure below . An embryo is a zygote that has already started to develop and grow. Early growth and development of a plant embryo inside a seed is called germination . The seed protects and nourishes the embryo and gives it a huge head start in the "race" of life. | C: germination. |
Elements are either metals, nonmetals, or what?
Here are the choices:
A. unstable metals
B. reactive metals
C. semimetals
D. partial metals | Elements are either metals, nonmetals, or semimetals. Each group is located in a different part of the periodic table. Another way to categorize the elements of the periodic table is shown in Figure 2.9 "Special Names for Sections of the Periodic Table". The first two columns on the left and the last six columns on the right are called the main group elements. The ten-column block between these columns contains the transition metals. The two rows beneath the main body of the periodic table contain the inner transition metals. The elements in these two rows are also referred to as, respectively, the lanthanide metals and the actinide metals. Figure 2.9 Special Names for Sections of the Periodic Table. | C: semimetals. |
Shield volcanoes often form along which locations?
Here are the choices:
A. convergent boundaries
B. fault lines
C. divergent plate boundaries
D. tectonic plates | Shield volcanoes often form along divergent plate boundaries. They also form at hot spots, like Hawaii. Shield volcano eruptions are non-explosive. | C: divergent plate boundaries. |
What is the study of the vital statistics of populations and how they change over time?
Here are the choices:
A. anthropology
B. demography
C. sociology
D. ethnography | B: demography. | |
Compared to free-floating bacteria, bacteria in biofilms often show increased resistance to what?
Here are the choices:
A. antibiotics and detergents
B. alcohol and detergents
C. acid and antibiotics
D. acid and detergents | Compared to free-floating bacteria, bacteria in biofilms often show increased resistance to antibiotics and detergents. Why do you think this might be the case?. | A: antibiotics and detergents. |
What type of energy travels in waves across space as well as through matter?
Here are the choices:
A. thermal energy
B. electromagnetic radiation
C. kinetic energy
D. mechanical radiation | Electromagnetic radiation is energy that travels in waves across space as well as through matter. Most of the electromagnetic radiation on Earth comes from the sun. Like other waves, electromagnetic waves are characterized by certain wavelengths and wave frequencies. Wavelength is the distance between two corresponding points on adjacent waves. Wave frequency is the number of waves that pass a fixed point in a given amount of time. Electromagnetic waves with shorter wavelengths have higher frequencies and more energy. | B: electromagnetic radiation. |
If an elephant and a boy are falling towards the ground, who will land first?
Here are the choices:
A. the boy
B. the elephant
C. both same time
D. neither will land | Both the elephant and the boy are falling to the ground because of gravity. The force of gravity (F grav ) is greater for the elephant than it is for the boy because the elephant is much more massive. Nonetheless, both of them will reach the ground at the same time (assuming they fall from the same height at the same time and there is no air resistance. ). | C: both same time. |
Designed to support the weight of the upper body when sitting and transfer this weight to the lower limbs when standing, what body structure consists of four bones: right and left hip bones, sacrum, and coccyx?
Here are the choices:
A. Chest
B. pelvis
C. lungs
D. tissues | Pelvis The pelvis consists of four bones: the right and left hip bones, the sacrum, and the coccyx (see Figure 8.12). The pelvis has several important functions. Its primary role is to support the weight of the upper body when sitting and to transfer this weight to the lower limbs when standing. It serves as an attachment point for trunk and lower limb muscles, and also protects the internal pelvic organs. When standing in the anatomical position, the pelvis is tilted anteriorly. In this position, the anterior superior iliac spines and the pubic tubercles lie in the same vertical plane, and the anterior (internal) surface of the sacrum faces forward and downward. The three areas of each hip bone, the ilium, pubis, and ischium, converge centrally to form a deep, cup-shaped cavity called the acetabulum. This is located on the lateral side of the hip bone and is part of the hip joint. The large opening in the anteroinferior hip bone between the ischium and pubis is the obturator foramen. This space is largely filled in by a layer of connective tissue and serves for the attachment of muscles on both its internal and external surfaces. Several ligaments unite the bones of the pelvis (Figure 8.14). The largely immobile sacroiliac joint is supported by a pair of strong ligaments that are attached between the sacrum and ilium portions of the hip bone. These are the anterior sacroiliac ligament on the anterior side of the joint and the posterior sacroiliac ligament on the posterior side. Also spanning the sacrum and hip bone are two additional ligaments. The sacrospinous ligament runs from the sacrum to the ischial spine, and the sacrotuberous ligament runs from the sacrum to the ischial tuberosity. These ligaments help to support and immobilize the sacrum as it carries the weight of the body. | B: pelvis. |
Of all the electromagnetic waves, which have the lowest frequencies?
Here are the choices:
A. X-rays
B. radio waves
C. gamma rays
D. ultraviolet rays | On the left side of the electromagnetic spectrum diagram are radio waves and microwaves. Radio waves have the longest wavelengths and lowest frequencies of all electromagnetic waves. They also have the least amount of energy. | B: radio waves. |
What do you call reversible changes that do not change matter’s chemical makeup or chemical properties?
Here are the choices:
A. physical changes
B. chemical changes
C. element changes
D. potential changes | A change of state occurs whenever matter changes from one state to another. Changes of state are physical changes in matter. They are reversible changes that do not change matter’s chemical makeup or chemical properties. | A: physical changes. |
Free atoms are spherical in shape, so the relative sizes of the elements can be compared by looking at each atom's atomic what?
Here are the choices:
A. weight
B. radius
C. axis
D. angles | One important characteristic that determines the way in which elements behave is the total size of each atom. Free atoms are spherical in shape, so the relative sizes of the elements can be compared by looking at each atom's atomic radius , which is the distance from an atom's nucleus to the electrons in the outermost orbitals. You might expect atoms to generally grow larger as they go up in atomic number (which is equal to the total number of electrons in the neutral atom). Indeed, if you look at a single group of the periodic table, this trend holds true. Iodine is larger than bromine, which is in turn larger than chlorine and fluorine. In the case of a single group, each successive row places electrons in a higher principal energy level. Since higher energy levels are farther from the nucleus on average, this results in a larger total volume occupied by the atom. | B: radius. |
What types of energy is released during a chemical reaction?
Here are the choices:
A. heat, electricity, light
B. temperature , electricity , light
C. human, magnetic, electrical
D. magnetism, electricity, light | All chemical reactions involve energy. Some chemical reactions consume energy, whereas other chemical reactions release energy. Chemical reactions can be either spontaneous, which do not require an input of energy, or non-spontaneous, which does require an input of some type of energy. Energy may be in the form of heat, light or electricity. Each of the energy changes that occur during a reaction are graphed in Figure below . In the reaction on the left, energy is released. In the reaction on the right, energy is consumed. | A: heat, electricity, light. |
What is the most common type of organic compound?
Here are the choices:
A. lipids
B. proteins
C. hydrocarbons
D. carbohydrates | Carbohydrates are the most common type of organic compound. A carbohydrate is an organic compound such as sugar or starch, and is used to store energy. Like most organic compounds, carbohydrates are built of small, repeating units that form bonds with each other to make a larger molecule. In the case of carbohydrates, the small repeating units are called monosaccharides. | D: carbohydrates. |
Hormones, ions, and neurotransmitters are all types of what?
Here are the choices:
A. pathogens
B. nutrients
C. chemical signals
D. proteins | The type of chemical signal a cell will send differs depending on the distance the message needs to go. For example, hormones , ions, and neurotransmitters are all types of signals that are sent depending on the distance the message needs to go. Endocrine signals are hormones, produced by endocrine organs. These signals travel through the blood stream to reach all parts of the body. | C: chemical signals. |
What explains why water molecules tend to stick together?
Here are the choices:
A. mineral bonds
B. covalent bonds
C. helium bonds
D. hydrogen bonds | Hydrogen bonds between water molecules explain some of water’s properties. For example, hydrogen bonds explain why water molecules tend to stick together. Have you ever watched water drip from a leaky faucet or from a melting icicle? If you have, then you know that water always falls in drops rather than as separate molecules. The dew drops in Figure below are another example of water molecules sticking together. | D: hydrogen bonds. |
The maturing follicle, containing a fluid-filled cavity, enlarges, forming a bulge near the surface of what?
Here are the choices:
A. the abdomen
B. the pelvis
C. the vagina
D. the ovary | D: the ovary. | |
Storm surge is very high water located in the low pressure eye of what?
Here are the choices:
A. tornados
B. earthquakes
C. hurricanes
D. eruptions | So much rain falling so fast causes some of the damage from a hurricane. But a lot of the damage is caused by storm surge. Storm surge is very high water located in the low pressure eye of the hurricane. The very low pressure of the eye allows the water level to rise above normal sea level. Storm surge can cause flooding when it reaches land ( Figure below ). High winds do a great deal of damage in hurricanes. High winds can also create very big waves. If the large waves are atop a storm surge, the high water can flood the shore. If the storm happens to occur at high tide, the water will rise even higher. | C: hurricanes. |
What is a waste product from fossil fuel burning?
Here are the choices:
A. oxidation
B. co2 emissions
C. smog
D. hydrogen gas | People themselves are also affected by the large size of the human population. Some people have a lot; some have very little. Many people refer to the abundance of luxury items in some people’s lives as over-consumption . People in developed nations use 32 times more resources than people in the developing countries of the world. The symbol of this is CO 2 emissions, which are a waste product from fossil fuel burning. Populations that burn the most fossil fuels have a high standard of living. | B: co2 emissions. |
Carbon dioxide is an example of a material that easily undergoes what?
Here are the choices:
A. spontaneous mutation
B. decomposition
C. amplification
D. sublimation | Carbon dioxide is an example of a material that easily undergoes sublimation. | D: sublimation. |
What is the term for daily cycles of behavior, like the sleep-wake cycle?
Here are the choices:
A. circadian rhythms
B. variable rhythms
C. daily rhythms
D. behavioral rhythms | Animals may eat and drink at certain times of day as well. Humans have daily cycles of behavior, too. Most people start to get sleepy after dark and have a hard time sleeping when it is light outside. Daily cycles of behavior are called circadian rhythms . | A: circadian rhythms. |
What organ senses sound?
Here are the choices:
A. eyes
B. brain
C. teeth
D. ear | Hearing is the ability to sense sound waves, and the ear is the organ that senses sound. Sound waves enter the auditory canal and travel to the eardrum (see Figure below ). They strike the eardrum and make it vibrate. The vibrations then travel through several other structures inside the ear and reach the cochlea. The cochlea is a coiled tube filled with liquid. The liquid moves in response to the vibrations, causing tiny hair cells lining the cochlea to bend. In response, the hair cells send nerve impulses to the auditory nerve, which carries the impulses to the brain. The brain interprets the impulses and “tells” us what we are hearing. | D: ear. |
The total energy assimilated by an ecosystem in a give period is known as what?
Here are the choices:
A. mean primary production
B. median primary production
C. gross primary production
D. size primary production | C: gross primary production. | |
Class bivalvia (“two shells”) includes clams, oysters, mussels, scallops, and these?
Here are the choices:
A. crabs
B. geoducks
C. octopuss
D. grendels | Class Bivalvia (“two shells”) includes clams, oysters, mussels, scallops, and geoducks. Members of this class are found in marine as well as freshwater habitats. As the name suggests, bivalves are enclosed in a pair of shells (valves are commonly called “shells”) that are hinged at the dorsal end by shell ligaments as well as shell teeth (Figure 28.22). The overall morphology is laterally flattened, and the head region is poorly developed. Eyespots and statocysts may be absent in some species. Since these animals are suspension feeders, a radula is absent in this class of mollusks. Respiration is facilitated by a pair of ctenidia, whereas excretion and osmoregulation are brought about by a pair of nephridia. Bivalves often possess a large mantle cavity. In some species, the posterior edges of the mantle may fuse to form two siphons that serve to take in and exude water. | B: geoducks. |
When does a caldera form?
Here are the choices:
A. when faults form
B. after an eruption
C. after a hurricane
D. before an eruption | A caldera forms after a massive eruption. The top of the volcano collapses, forming a basin. | B: after an eruption. |
The mass lost in mass defect has gone into energy called what?
Here are the choices:
A. momentum
B. enthalpy
C. binding energy
D. kinetic energy | The mass lost in mass defect has gone into energy that is called binding energy. | C: binding energy. |
What is used for the fermentation process that makes beer, wine, and bread?
Here are the choices:
A. whey
B. fungi
C. barley
D. yeast | Yeast are used for the fermentation process that makes beer, wine, and bread. | D: yeast. |
Plant viruses can seriously disrupt crop growth and development, significantly affecting our what?
Here are the choices:
A. food supply
B. fuel supply
C. air supply
D. harvest supply | Plant viruses can seriously disrupt crop growth and development, significantly affecting our food supply. They are responsible for poor crop quality and quantity globally, and can bring about huge economic losses annually. Others viruses may damage plants used in landscaping. Some viruses that infect agricultural food plants include the name of the plant they infect, such as tomato spotted wilt virus, bean common mosaic virus, and cucumber mosaic virus. In plants used for landscaping, two of the most common viruses are peony ring spot and rose mosaic virus. There are far too many plant viruses to discuss each in detail, but symptoms of bean common mosaic virus result in lowered bean production and stunted, unproductive plants. In the ornamental rose, the rose mosaic disease causes wavy yellow lines and colored splotches on the leaves of the plant. | A: food supply. |
In the past, biologists grouped living organisms into five kingdoms: animals, plants, fungi, protists, and what?
Here are the choices:
A. bacteria
B. lizards
C. pathogens
D. trees | Carl Woese and the Phylogenetic Tree In the past, biologists grouped living organisms into five kingdoms: animals, plants, fungi, protists, and bacteria. The organizational scheme was based mainly on physical features, as opposed to physiology, biochemistry, or molecular biology, all of which are used by modern systematics. The pioneering work of American microbiologist Carl Woese in the early 1970s has shown, however, that life on Earth has evolved along three lineages, now called domains—Bacteria, Archaea, and Eukarya. The first two are prokaryotic cells with microbes that lack membrane-enclosed nuclei and organelles. The third domain contains the eukaryotes and includes unicellular microorganisms together with the four original kingdoms (excluding bacteria). Woese defined Archaea as a new domain, and this resulted in a new taxonomic tree (Figure 1.17). Many organisms belonging to the Archaea domain live under extreme conditions and are called extremophiles. To construct his tree, Woese used genetic relationships rather than similarities based on morphology (shape). Woese’s tree was constructed from comparative sequencing of the genes that are universally distributed, present in every organism, and conserved (meaning that these genes have remained essentially unchanged throughout evolution). Woese’s approach was revolutionary because comparisons of physical features are insufficient to differentiate between the prokaryotes that appear fairly similar in spite of their tremendous biochemical diversity and genetic variability (Figure 1.18). The comparison of homologous DNA and RNA sequences provided Woese with a sensitive device that revealed the extensive variability of prokaryotes, and which justified the separation of the prokaryotes into two domains: bacteria and archaea. | A: bacteria. |
What kind of joints allow for a wide range of flexibility?
Here are the choices:
A. ball and socket
B. lever
C. pivot
D. anchor | Socket diagram: Pearson Scott Foresman; Joint diagram: Zachary Wilson. Ball and socket joints allow for a wide range of flexibility . Socket diagram: Public Domain; Joint diagram: CC BY-NC 3.0. | A: ball and socket. |
The human body wants to maintain equilibrium or balance, also known as what?
Here are the choices:
A. perfection
B. heterostasis
C. homeostasis
D. stability | Homeostasis The goal of homeostasis is the maintenance of equilibrium around a specific value of some aspect of the body or its cells called a set point. While there are normal fluctuations from the set point, the body’s systems will usually attempt to go back to this point. A change in the internal or external environment is called a stimulus and is detected by a receptor; the response of the system is to adjust the activities of the system so the value moves back toward the set point. For instance, if the body becomes too warm, adjustments are made to cool the animal. If glucose levels in the blood rise after a meal, adjustments are made to lower them and to get the nutrient into tissues that need it or to store it for later use. When a change occurs in an animal’s environment, an adjustment must be made so that the internal environment of the body and cells remains stable. The receptor that senses the change in the environment is part of a feedback mechanism. The stimulus—temperature, glucose, or calcium levels—is detected by the receptor. The receptor sends information to a control center, often the brain, which relays appropriate signals to an effector organ that is able to cause an appropriate change, either up or down, depending on the information the sensor was sending. | C: homeostasis. |
Natural gas, such as those burned by gas stoves, is composed mostly of this?
Here are the choices:
A. carbon monoxide
B. sulfur
C. oxygen
D. methane | The burner on a gas stove burns with a pretty blue flame like the one pictured in the opening image. The fuel burned by most gas stoves is natural gas, which consists mainly of methane. Methane is a compound that contains only carbon and hydrogen. Like many other compounds that consist of just these two elements, methane is used for fuel because it burns very easily. Methane is an example of a covalent compound. | D: methane. |
Which is the process through which leaves collect sunlight and make food?
Here are the choices:
A. Greenhouse
B. photosynthesis
C. richness
D. compress | Leaves are the keys not only to plant life but to virtually all life on land. The primary role of leaves is to collect sunlight and make food by photosynthesis. Leaves vary in size, shape, and how they are arranged on stems. You can see examples of different types of leaves in Figure below . | B: photosynthesis. |
What model describes the structure of the plasma membrane as a mosaic of components?
Here are the choices:
A. sensors mosaic model
B. solid mosaic model
C. fluid mosaic model
D. coolant mosaic model | Fluid Mosaic Model In 1972, S. Singer and Garth L. Nicolson proposed a new model of the plasma membrane that, compared to earlier understanding, better explained both microscopic observations and the function of the plasma membrane. This was called the fluid mosaic model. The model has evolved somewhat over time, but still best accounts for the structure and functions of the plasma membrane as we now understand them. The fluid mosaic model describes the structure of the plasma membrane as a mosaic of components—including phospholipids, cholesterol, proteins, and carbohydrates—in which the components are able to flow and change position, while maintaining the basic integrity of the membrane. Both phospholipid molecules and embedded proteins are able to diffuse rapidly and laterally in the membrane. The fluidity of the plasma membrane is necessary for the activities of certain enzymes and transport molecules within the membrane. Plasma membranes range from 5–10 nm thick. As a comparison, human red blood cells, visible via light microscopy, are approximately 8 µm thick, or approximately 1,000 times thicker than a plasma membrane. (Figure 3.18). | C: fluid mosaic model. |
The hot liquid rock on the surface is called what?
Here are the choices:
A. flow
B. volcano
C. lava
D. Molten | C: lava. | |
The first consumption of breast milk or formula floods the newborn’s sterile gastrointestinal tract with beneficial what?
Here are the choices:
A. bacteria
B. pathogens
C. disease
D. oxygen | 28.5 Adjustments of the Infant at Birth and Postnatal Stages The first breath a newborn takes at birth inflates the lungs and dramatically alters the circulatory system, closing the three shunts that directed oxygenated blood away from the lungs and liver during fetal life. Clamping and cutting the umbilical cord collapses the three umbilical blood vessels. The proximal umbilical arteries remain a part of the circulatory system, whereas the distal umbilical arteries and the umbilical vein become fibrotic. The newborn keeps warm by breaking down brown adipose tissue in the process of nonshivering thermogenesis. The first consumption of breast milk or formula floods the newborn’s sterile gastrointestinal tract with beneficial bacteria that eventually establish themselves as the bacterial flora, which aid in digestion. | A: bacteria. |
Clouds are formed from what?
Here are the choices:
A. snow flakes
B. ice crystals
C. dust particles
D. water droplets | Rising air currents carry water vapor into the atmosphere. As the water vapor rises in the atmosphere, it cools and condenses. Condensation is the process in which water vapor changes to tiny droplets of liquid water. The water droplets may form clouds. If the droplets get big enough, they fall as precipitation. | D: water droplets. |
After spermatids form, they move where to mature into sperm?
Here are the choices:
A. into the prostate
B. into the volaris
C. into the epididymis
D. into the vans deferens | After spermatids form, they move into the epididymis to mature into sperm, like the one shown in Figure below . The spermatids grow a tail and lose excess cytoplasm from the head. When a sperm is mature, the tail can rotate like a propeller, so the sperm can propel itself forward. Mitochondria in the connecting piece produce the energy (ATP) needed for movement. The head of the mature sperm consists mainly of the nucleus, which carries copies of the father’s chromosomes. The part of the head called the acrosome produces enzymes that help the sperm head penetrate an egg. | C: into the epididymis. |
Matter can exist either as a pure substance or as a combination of what?
Here are the choices:
A. different vapors
B. different substances
C. much substances
D. Different Liquids | The properties of matter, both physical and chemical, depend on the substances that matter is made of. Matter can exist either as a pure substance or as a combination of different substances. | B: different substances. |
What is the separation of compounds on the basis of their solubilities in a given solvent?
Here are the choices:
A. fractional mass
B. fractional crystallization
C. volatile crystallization
D. solvent law | temperature. In fact, the magnitudes of the changes in both enthalpy and entropy for dissolution are temperature dependent. Because the solubility of a compound is ultimately determined by relatively small differences between large numbers, there is generally no good way to predict how the solubility will vary with temperature. The variation of solubility with temperature has been measured for a wide range of compounds, and the results are published in many standard reference books. Chemists are often able to use this information to separate the components of a mixture byfractional crystallization, the separation of compounds on the basis of their solubilities in a given solvent. For example, if we have a mixture of 150 g of sodium acetate (CH3CO2Na) and 50 g of KBr, we can separate the two compounds by dissolving the mixture in 100 g of water at 80°C and then cooling the solution slowly to 0°C. According to the temperature curves in Figure 13.9 "Solubilities of Several Inorganic and Organic Solids in Water as a Function of Temperature", both compounds dissolve in water at 80°C, and all 50 g of KBr remains in solution at 0°C. Only about 36 g of CH3CO2Na are soluble in 100 g of water at 0°C, however, so approximately 114 g (150 g − 36 g) of CH3CO2Na crystallizes out on cooling. The crystals can then be separated by filtration. Thus fractional crystallization allows us to recover about 75% of the original CH3CO2Na in essentially pure form in only one step. Fractional crystallization is a common technique for purifying compounds as diverse as those shown in Figure 13.9 "Solubilities of Several Inorganic and Organic Solids in Water as a Function of Temperature" and from antibiotics to enzymes. For the technique to work properly, the compound of interest must be more soluble at high temperature than at low temperature, so that lowering the temperature causes it to crystallize out of solution. In addition, the impurities must be more soluble than the compound of interest (as was KBr in this example) and preferably present in relatively small amounts. | B: fractional crystallization. |
Triploblasts include a broad range of animals, from flatworms to arthropods to what?
Here are the choices:
A. vertebrates
B. cells
C. mammals
D. invertebrates | A: vertebrates. | |
What is the release of particles and/or energy from the nucleus of an atom described as?
Here are the choices:
A. radioactivity
B. temperature
C. kinetic energy
D. momentum | Radioactivity involves the release of particles and/or energy from the nucleus of an atom. | A: radioactivity. |
Through which process do behaviors that improve fitness increase?
Here are the choices:
A. mutation
B. natural selection
C. adaptation
D. succession | Most animal behaviors are controlled by both genes and experiences in a given environment. To the extent that behaviors are controlled by genes, they may evolve. Behaviors that improve fitness increase through natural selection. | B: natural selection. |
Enzymes - proteins which speed up what?
Here are the choices:
A. liquid reactions
B. physical reactions
C. chemical reactions
D. crystals reactions | enzymes - proteins which speed up chemical reactions. | C: chemical reactions. |
What do you call the sudden flow of mud down a slope because of gravity?
Here are the choices:
A. mudslide
B. typhoon
C. rockflow
D. mountainside | A mudslide is the sudden flow of mud down a slope because of gravity. Mudslides occur where the soil is mostly clay. Like landslides, mudslides usually occur when the soil is wet. Wet clay forms very slippery mud that slides easily. You can see an example of a mudslide in Figure below . | A: mudslide. |
What causes acid rain, ozone depletion, and global warming?
Here are the choices:
A. air pollution
B. water pollution
C. radiation
D. ozone layer | Air pollution consists of chemical substances and particles released into the air, mainly by human actions. The major cause of outdoor air pollution is the burning of fossil fuels. Indoor air can also be polluted. Air pollution, in turn, causes acid rain, ozone depletion, and global warming. | A: air pollution. |
The amniotes are distinguished from amphibians by the presence of a terrestrially adapted egg protected by what?
Here are the choices:
A. albumen
B. yolk
C. hard shell
D. amniotic membranes | 29.4 Reptiles The amniotes are distinguished from amphibians by the presence of a terrestrially adapted egg protected by amniotic membranes. The amniotes include reptiles, birds, and mammals. The early amniotes diverged into two main lines soon after the first amniotes arose. The initial split was into synapsids (mammals) and sauropsids. Sauropsids can be further divided into anapsids (turtles) and diapsids (birds and reptiles). Reptiles are tetrapods either having four limbs or descending from such. Limbless reptiles (snakes) are classified as tetrapods, as they are descended from four-limbed organisms. One of the key adaptations that permitted reptiles to live on land was the development of scaly skin containing the protein keratin, which prevented water loss from the skin. Reptilia includes four living clades: Crocodilia (crocodiles and alligators), Sphenodontia (tuataras), Squamata (lizards and snakes), and Testudines (turtles). | D: amniotic membranes. |
The cells of what basic plant structure lack chloroplasts?
Here are the choices:
A. leaf
B. ferns
C. stem
D. root | D: root. | |
What muscle in the chest helps inflate and deflate the lungs?
Here are the choices:
A. heart
B. diaphragm
C. pectoral
D. cartilage | Mammals breathe with the help of a diaphragm. This is the large muscle that extends across the bottom of the chest below the lungs. When the diaphragm contracts, it increases the volume of the chest. This decreases pressure on the lungs and allows air to flow in. When the diaphragm relaxes, it decreases the volume of the chest. This increases pressure on the lungs and forces air out. | B: diaphragm. |
Where in the lungs does gas exchange between the air and blood takes place?
Here are the choices:
A. alveoli
B. left lobe
C. bronchial tube
D. ganglion | The alveoli in the lungs are where gas exchange between the air and blood takes place. Each alveolus is surrounded by a network of capillaries. When you inhale, air in the alveoli has a greater concentration of oxygen than does blood in the capillaries. The difference in oxygen concentration causes oxygen to diffuse from the air into the blood. You can see how this occurs in Figure below . | A: alveoli. |
What are hollow cylinders and are the thickest of the cytoskeleton structures?
Here are the choices:
A. cytoplasm
B. microtubules
C. vesicles
D. nucleotides | Microtubules , shown in Figure below (a) , are hollow cylinders and are the thickest of the cytoskeleton structures. They are most commonly made of filaments which are polymers of alpha and beta tubulin, and radiate outwards from an area near the nucleus called the centrosome. Tubulin is the protein that forms microtubules. Two forms of tubulin, alpha and beta, form dimers (pairs) which come together to form the hollow cylinders. The cylinders are twisted around each other to form the microtubules. Microtubules help the cell keep its shape. They hold organelles in place and allow them to move around the cell, and they form the mitotic spindle during cell division. Microtubules also make up parts of cilia and flagella, the organelles that help a cell move. | B: microtubules. |
What simple sugar is the cell's primary source of energy?
Here are the choices:
A. chloride
B. nicotine
C. glucose
D. carbon | Molecular formulas tell us how many atoms of each element are present in one molecule of a molecular compound. In many cases, the molecular formula is the same as the empirical formula. For example, the molecular formula of methane is CH 4 , and because 1:4 is the smallest whole-number ratio that can be written for this compound, that is also its empirical formula. Sometimes, however, the molecular formula is a simple whole-number multiple of the empirical formula. Acetic acid is an organic acid that gives vinegar its distinctive taste and smell. Its molecular formula is C 2 H 4 O 2 . Glucose is a simple sugar that cells use as their primary source of energy. Its molecular formula is C 6 H 12 O 6 . The structures of both molecules are shown in Figure below . They are very different compounds, yet both have the same empirical formula, CH 2 O. | C: glucose. |
What is the approximate population on the earth?
Here are the choices:
A. 9 trillion
B. 7.3 billion
C. 41 billion
D. 7 billion | There are approximately 7 billion humans on the planet. How long would it take some bacteria to make 7 billion copies of themselves?. | D: 7 billion. |
A change in the sequence of bases in dna or rna is called a what?
Here are the choices:
A. infection
B. accumulation
C. mutation
D. isolation | A change in the sequence of bases in DNA or RNA is called a mutation . Does the word mutation make you think of science fiction and bug-eyed monsters? Think again. Everyone has mutations. In fact, most people have dozens or even hundreds of mutations in their DNA. Mutations are essential for evolution to occur. They are the ultimate source of all new genetic material in a species. Although most mutations have no effect on the organisms in which they occur, some mutations are beneficial. Even harmful mutations rarely cause drastic changes in organisms. | C: mutation. |
What is the product of microfilament movement powered by chemical energy?
Here are the choices:
A. nerve stimulation
B. muscle fusion
C. muscle contraction
D. blood circulation | C: muscle contraction. | |
What is a measure of how much energy is needed to change the temperature of a substance?
Here are the choices:
A. specific gravity
B. momentum
C. thermal potential
D. specific heat | where the mass, specific heat, and change in temperature are multiplied together. Specific heat is a measure of how much energy is needed to change the temperature of a substance; the larger the specific heat, the more energy is needed to change the temperature. The units for specific heat are depending on what the unit of ΔTis. You may note a departure from the insistence that temperature be expressed in Kelvin. That is because a change in temperature has the same value whether the temperatures are expressed in degrees Celsius or kelvins. | D: specific heat. |
What is the common term for animals in the phylum porifera?
Here are the choices:
A. sharks
B. crustaceans
C. corals
D. sponges | D: sponges. | |
What term is used to describe a change in the characteristics of living things over time?
Here are the choices:
A. evolution
B. reproduction
C. generation
D. customization | Evolution is a change in the characteristics of living things over time. Evolution occurs by natural selection. | A: evolution. |
What can accept a wide range of carbohydrates for catabolism?
Here are the choices:
A. photosynthesis
B. glycolysis
C. enzymes
D. cellular respiration | B: glycolysis. | |
What includes all living things within all their environments, including everywhere life exists, from the upper atmosphere, to the top of the soil, to ocean bottoms?
Here are the choices:
A. biosphere
B. biome
C. community
D. habitat | The biosphere includes all living things within all of their environments. It includes every part of the environment where life exists, from the upper reaches of the atmosphere to the top few meters of soil, to the bottoms of the oceans. An ecosystem is made up of the relationships among smaller groups of organisms with each other, and with their environment. Scientists often speak of the interrelatedness of living things, because, according to evolutionary theory, organisms adapt to their environment, and they must also adapt to other organisms in that environment. | A: biosphere. |
What is unique and found in all living things because it can form up to four covalent bonds between atoms or molecules?
Here are the choices:
A. oxygen
B. carbon
C. hydrogen
D. potassium | Chapter 2 1 Figure 2.3 Carbon-12 has six neutrons. Carbon-13 has seven neutrons. 3 Figure 2.24 C 4 A 6 C 8 D 10 C 12 D 14 Ionic bonds are created between ions. The electrons are not shared between the atoms, but rather are associated more with one ion than the other. Ionic bonds are strong bonds, but are weaker than covalent bonds, meaning it takes less energy to break an ionic bond compared with a covalent one. 16 Buffers absorb the free hydrogen ions and hydroxide ions that result from chemical reactions. Because they can bond these ions, they prevent increases or decreases in pH. An example of a buffer system is the bicarbonate system in the human body. This system is able to absorb hydrogen and hydroxide ions to prevent changes in pH and keep cells functioning properly. 18 Carbon is unique and found in all living things because it can form up to four covalent bonds between atoms or molecules. These can be nonpolar or polar covalent bonds, and they allow for the formation of long chains of carbon molecules that combine to form proteins and DNA. | B: carbon. |
What kind of rock is gypsum?
Here are the choices:
A. basalt
B. igneous
C. metamorphic
D. sedimentary | Gypsum, with its rose-like structure, is a chemical sedimentary rock. | D: sedimentary. |
What component of a prokaryote is unique in molecular composition and mechanism of propulsion?
Here are the choices:
A. the amoeba
B. the sporangia
C. the membrane
D. the flagella | D: the flagella. | |
The sum of the masses of the atoms in the formula is referred to as what?
Here are the choices:
A. nucleus mass
B. molecular mass
C. magnetic mass
D. atomic mass | The molecular mass is the sum of the masses of the atoms in the formula. | B: molecular mass. |
What size of ring will a summer drought cause in a tree?
Here are the choices:
A. smaller
B. giant
C. medium
D. larger | You can tell other things from tree rings too. In a good year a tree will produce a wide ring. A summer drought will produce a smaller ring. These variations will appear in all trees in a region. The same pattern can be found in all the trees in the area. This pattern helps scientist to identify a particular time period. | A: smaller. |
What is the technical term for species that produce their own body heat and regulate their internal temperature independently of the outside temperature?
Here are the choices:
A. osmotic
B. hydrostatic
C. endothermic
D. Phototrophic | 29.5 Birds Birds are endothermic, meaning they produce their own body heat and regulate their internal temperature independently of the external temperature. Feathers not only act as insulation but also allow for flight, providing lift with secondary feathers and thrust with primary feathers. Pneumatic bones are bones that are hollow rather than filled with tissue, containing air spaces that are sometimes connected to air sacs. Airflow through bird lungs travels in one direction, creating a crosscurrent exchange with the blood. Birds are diapsids and belong to a group called the archosaurs. Birds are thought to have evolved from theropod dinosaurs. The oldest known fossil of a bird is that of Archaeopteryx, which is from the Jurassic period. Modern birds are now classified into two groups, Paleognathae and Neognathae. | C: endothermic. |
What is the transparent outer covering of the eye?
Here are the choices:
A. pupil
B. retina
C. iris
D. cornea | The cornea is the transparent outer covering of the eye. It protects the eye and also acts as a convex lens, helping to focus light that enters the eye. | D: cornea. |
Photoreceptors in each ocellus receive light only through the opening where there are none of which cells?
Here are the choices:
A. opqaue
B. secreted
C. clear
D. pigmented | D: pigmented. | |
What helps form the walls of internal organs such as the heart and stomach?
Here are the choices:
A. blood
B. muscles
C. valves
D. tissues | B: muscles. |
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