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Many adults and some children suffer from a deficiency of lactase. These individuals are said to be lactose intolerant because they cannot digest the lactose found in milk. A more serious problem is the genetic disease galactosemia, which results from the absence of an enzyme needed to convert galactose to glucose. Cer... | allenai/sciq |
Because electricity can be so dangerous, safety features are built into modern electric circuits and devices. They include three-prong plugs, circuit breakers, and GFCI outlets. You can read about these three safety features in the Figure below . You can learn more about electric safety features in the home by watching... | allenai/sciq |
Catabolic Reactions Catabolic reactions break down large organic molecules into smaller molecules, releasing the energy contained in the chemical bonds. These energy releases (conversions) are not 100 percent efficient. The amount of energy released is less than the total amount contained in the molecule. Approximately... | allenai/sciq |
Selective precipitation can also be used in qualitative analysis. In this method, reagents are added to an unknown chemical mixture in order to induce precipitation. Certain reagents cause specific ions to precipitate out; therefore, the addition of the reagent can be used to determine whether the ion is present in the... | allenai/sciq |
Climate change in Earth history was due to natural processes. Recent global warming is due mainly to human actions. The burning of fossil fuels releases greenhouse gases into the air. This creates greater greenhouse effect and global warming. | allenai/sciq |
The haploid life cycle ( Figure below ) is the simplest life cycle. It is found in many single-celled organisms. Organisms with a haploid life cycle spend the majority of their lives as haploid gametes. When the haploid gametes fuse, they form a diploid zygote. It quickly undergoes meiosis to produce more haploid gamet... | allenai/sciq |
Gravity keeps the Moon orbiting Earth. Gravity keeps the planets orbiting the Sun. | allenai/sciq |
Ionic bonds are formed by the attraction between oppositely charged ions. | allenai/sciq |
The hypothalamus also produces hormones that directly regulate body processes. For example, it produces antidiuretic hormone. This hormone travels to the kidneys and stimulates them to conserve water by producing more concentrated urine. | allenai/sciq |
Take a close look at this gorilla hand. The similarities to a human hand are remarkable. Comparing anatomy, and characterizing the similarities and differences, provides evidence of evolution. | allenai/sciq |
The majority of arthropods are insects (Class Insecta). In fact, more than half of all known organisms are insects. There may be more than 10 million insect species in the world, although most of them have not yet been identified. In terms of their numbers and diversity, insects clearly are the dominant animals in the ... | allenai/sciq |
Saturn’s composition is similar to Jupiter's. The planet is made mostly of hydrogen and helium. These elements are gases in the outer layers and liquids in the deeper layers. Saturn may also have a small solid core. Saturn's upper atmosphere has clouds in bands of different colors. These clouds rotate rapidly around th... | allenai/sciq |
Alkenes Organic compounds that contain one or more double or triple bonds between carbon atoms are described as unsaturated. You have likely heard of unsaturated fats. These are complex organic molecules with long chains of carbon atoms, which contain at least one double bond between carbon atoms. Unsaturated hydrocarb... | allenai/sciq |
The two materials do have at least one thing in common. The atoms in the materials are held together by covalent bonds. These bonds consist of electrons shared between two or more atoms. Unlike ionic bonds, where electrons are either lost or gained by an atom to form charged ions, electrons in covalent compounds are sh... | allenai/sciq |
Viscosity (η) is the resistance of a liquid to flow. Some liquids, such as gasoline, ethanol, and water, flow very readily and hence have a low viscosity. Others, such as motor oil, molasses, and maple syrup, flow very slowly and have a high viscosity. The two most common methods for evaluating the viscosity of a liqui... | allenai/sciq |
Atoms have a mass that is based largely on the number of protons and neutrons in their nucleus. | allenai/sciq |
Annelids called polychaete worms live on the ocean floor. They may be filter feeders, predators, or scavengers. The amazing feather duster worm in Figure below is a polychaete that has a fan-like crown of tentacles for filter feeding. | allenai/sciq |
Biogeography is the study of how and why plants and animals live where they do. It provides more evidence for evolution. Let’s consider the camel family as an example. | allenai/sciq |
Muscles That Position the Pectoral Girdle Muscles that position the pectoral girdle are located either on the anterior thorax or on the posterior thorax (Figure 11.22 and Table 11.8). The anterior muscles include the subclavius, pectoralis minor, and serratus anterior. The posterior muscles include the trapezius, rhomb... | allenai/sciq |
Glucose is the energy-rich product of photosynthesis, a universal food for life. It is also the primary form in which your bloodstream delivers energy to every cell in your body. | allenai/sciq |
The oxygen enters the bloodstream from the alveoli , tiny sacs in the lungs where gas exchange takes place ( Figure below ). The transfer of oxygen into the blood is through simple diffusion. | allenai/sciq |
Fungi are simple eukaryotic organisms that consist of one or more cells. They include mushrooms and yeasts. Human diseases caused by fungi include ringworm and athlete’s foot. Both are skin diseases that are not usually serious. A ringworm infection is pictured below ( Figure below ). A more serious fungus disease is h... | allenai/sciq |
A car’s gas pedal, like the one in Figure below , is sometimes called the accelerator. That’s because it controls the acceleration of the car. Pressing down on the gas pedal gives the car more gas and causes the car to speed up. Letting up on the gas pedal gives the car less gas and causes the car to slow down. Wheneve... | allenai/sciq |
Bronchitis is an inflammation of the bronchi, the air passages that conduct air into the lungs. The bronchi become red and swollen with infection. Acute bronchitis is usually caused by viruses or bacteria, and may last several days or weeks. It is characterized by a cough that produces phlegm, or mucus. Symptoms includ... | allenai/sciq |
Primates are generally divided into prosimian and non-prosimian primates. | allenai/sciq |
In some places, the oceanic crust comes up to a continent. The moving crust pushes that continent away from the ridge axis as well. If the moving oceanic crust reaches a deep sea trench, the crust sinks into the mantle. The creation and destruction of oceanic crust is the reason that continents move. | allenai/sciq |
Looking at different types of competition, ecologists developed the competitive exclusion principle . The principle states that species less suited to compete for resources will either adapt, move from the area, or die out. In order for two species within the same area to coexist, they may adapt by developing different... | allenai/sciq |
You can follow the operation of an electricity-generating fission reactor in the image above. The reactor core is submerged in a pool of water. The heat from the fission reaction heats the water, which is pumped into a heat exchange container. There the heated water boils the water in the heat exchanger. The produced s... | allenai/sciq |
A single-replacement reaction is one in which an element replaces another element in a compound. An element is in either the solid, liquid, or gas state and is not an ion. The example below shows the reaction of solid magnesium metal with aqueous silver nitrate to form aqueous magnesium nitrate and silver metal. | allenai/sciq |
Metallic Solids Metals are characterized by their ability to reflect light, called luster, their high electrical and thermal conductivity, their high heat capacity, and their malleability and ductility. Every lattice point in a pure metallic element is occupied by an atom of the same metal. The packing efficiency in me... | allenai/sciq |
Introduction Plants are as essential to human existence as land, water, and air. Without plants, our day-to-day lives would be impossible because without oxygen from photosynthesis, aerobic life cannot be sustained. From providing food and shelter to serving as a source of medicines, oils, perfumes, and industrial prod... | allenai/sciq |
It is estimated that 100 trillion bacteria live in the gut. This is more than the human cells that make up you. It has also been estimated that there are more bacteria in your mouth than people on the planet. There are over 7 billion people on the planet. | allenai/sciq |
Mammals have the ability to regulate body temperature. This is an advantage, as Earth’s climate went through sudden and dramatic changes. Mastodons, saber tooth tigers, hoofed mammals, whales, primates and eventually humans all lived during the Cenozoic Era ( Figure below ). | allenai/sciq |
The majority of the human genome is non-coding sequence. These sequences include regulatory sequences, and DNA with unknown functions. These sequences include tandem repeat elements known as satellite DNA , and transposons. Satellite DNA consists of very large arrays of tandemly repeating, non-coding DNA. The repeating... | allenai/sciq |
Oceanographers use bathymetric maps to show the features of the bottom of a body of water. | allenai/sciq |
Migration Migration is the long-range seasonal movement of animals. It is an evolved, adapted response to variation in resource availability, and it is a common phenomenon found in all major groups of animals. Birds fly south for the winter to get to warmer climates with sufficient food, and salmon migrate to their spa... | allenai/sciq |
Composite volcanoes are also called stratovolcanoes. This is because they are formed by alternating layers (strata) of magma and ash ( Figure below ). The magma that creates composite volcanoes tends to be thick. The steep sides form because the lava cannot flow too far from the vent. The thick magma may also create ex... | allenai/sciq |
When geologic and climatic conditions are changing, evolution may occur more quickly. Thus, long periods of little change may be interrupted by bursts of rapid change. This model of the timing of evolution is called punctuated equilibrium . It is better supported by the fossil record than is gradualism. | allenai/sciq |
Chinook winds ( Figure below ) occur when air is forced over a mountain range. Warm air rises over the Sierra Nevada in California, for example, because it is pushed eastward by the westerly winds. The air cools as it rises and precipitates. The air is now dry. It sinks down the far side of the mountains and may create... | allenai/sciq |
Clouds block sunlight in the day. Clouds trap heat in the atmosphere at night. | allenai/sciq |
The nervous system is made up of nerves. A nerve is a bundle of nerve cells. A nerve cell that carries messages is called a neuron. The messages carried by neurons are called nerve impulses. | allenai/sciq |
There are several traits shared by all arthropods. Arthropods have a complete digestive system. They also have a circulatory system and a nervous system. In addition, they have special organs for breathing and excreting wastes. Other traits of arthropods include:. | allenai/sciq |
Complex Tissue Structure A hallmark trait of animals is specialized structures that are differentiated to perform unique functions. As multicellular organisms, most animals develop specialized cells that group together into tissues with specialized functions. A tissue is a collection of similar cells that had a common ... | allenai/sciq |
Most biochemical molecules are macromolecules, meaning that they are very large. Some contain thousands of monomer molecules. | allenai/sciq |
The Spinal Cord The description of the CNS is concentrated on the structures of the brain, but the spinal cord is another major organ of the system. Whereas the brain develops out of expansions of the neural tube into primary and then secondary vesicles, the spinal cord maintains the tube structure and is only speciali... | allenai/sciq |
Laboratory testing has come to the local drug store or grocery store because of developments in chemistry. You can test your blood glucose using a simple portable device that runs a chemical test on the blood sample and tells you how much glucose is present, allowing a diabetic patient to regulate how much insulin to a... | allenai/sciq |
Any useful hypothesis will allow predictions based on reasoning. Reasoning can be broken down into two categories: deduction and induction. Most reasoning in science is formed through induction. | allenai/sciq |
Astronomers use imaging satellites to study and make maps of the Moon and other planets. | allenai/sciq |
Density is an important physical property of matter. It reflects how closely packed the particles of matter are. When particles are packed together more tightly, matter has greater density. Differences in density of matter explain many phenomena, not just why helium balloons rise. For example, differences in density of... | allenai/sciq |
Populations of viruses do not grow through cell division because they are not cells. Instead, they use the machinery and metabolism of a host cell to produce new copies of themselves. After infecting a host cell, a virion uses the cell’s ribosomes, enzymes, ATP, and other components to replicate. Viruses vary in how th... | allenai/sciq |
Some parasites kill their host, but most do not. It’s easy to see why. If a parasite kills its host, the parasite is also likely to die. Instead, parasites usually cause relatively minor damage to their host. | allenai/sciq |
An amorphous solid is a solid that lacks an ordered internal structure. | allenai/sciq |
Getting the same result when an experiment is repeated is called replication. If research results can be replicated, it means they are more likely to be correct. | allenai/sciq |
human body system that includes the skin, nails, and hair. | allenai/sciq |
In the chest, the trachea divides as it enters the lungs to form the right and left bronchi . The bronchi contain cartilage, which prevents them from collapsing. Mucus in the bronchi traps any remaining particles in air. Tiny, hair-like structures called cilia line the bronchi and sweep the particles and mucus toward t... | allenai/sciq |
Many objects have color because they contain pigments. A pigment is a substance that colors materials by reflecting light of certain wavelengths and absorbing light of other wavelengths. A very common pigment is the dark green pigment called chlorophyll, which is found in plants. Chlorophyll absorbs all but green wavel... | allenai/sciq |
Nuclear power is a controversial subject in California and most other places. Nuclear power has no pollutants including no carbon emissions. However, power plants are not always safe. The long-term disposal of wastes is a problem that has not yet been solved. The future of nuclear power is murky. Find out more at: http... | allenai/sciq |
The esophagus is a long, narrow tube that carries food from the pharynx to the stomach. It has no other purpose. Food moves through the esophagus because of peristalsis. At the lower end of the esophagus, a circular muscle, called a sphincter, controls the opening to the stomach. The sphincter relaxes to let food pass ... | allenai/sciq |
The temperature at which condensation of water vapor occurs is called the dew point. The dew point varies depending on air temperature and moisture content. | allenai/sciq |
Alkenes have double bonds; alkynes have triple bonds. Both undergo addition reactions. | allenai/sciq |
Weathering may concentrate some resources. In tropical climates, chemical weathering can be intense. Some minerals dissolve and water carries them away. This leaves behind the materials that are not soluble. Bauxite is aluminum oxide that collects this way. Bauxite is our main source of aluminum ore. | allenai/sciq |
Several lethal viruses that cause viral hemorrhagic fever have been discovered, two of which are shown in the Figure below . Ebola outbreaks have been limited mainly to remote areas of the world. However, they have gained extensive media attention because of the high mortality rate—23 percent to 90 percent—depending on... | allenai/sciq |
Cell division is simpler in prokaryotes than eukaryotes because prokaryotic cells themselves are simpler. Prokaryotic cells have a single circular chromosome, no nucleus, and few other organelles. Eukaryotic cells, in contrast, have multiple chromosomes contained within a nucleus, and many other organelles. All of thes... | allenai/sciq |
The axon of many neurons has an outer layer called a myelin sheath (see Figure above ). Myelin is a lipid produced by a type of a glial cell known as a Schwann cell. The myelin sheath acts like a layer of insulation, similar to the plastic that encases an electrical cord. Regularly spaced nodes, or gaps, in the myelin ... | allenai/sciq |
New species arise in the process of speciation. Allopatric speciation occurs when some members of a species become geographically separated. They then evolve genetic differences. If the differences prevent them from interbreeding with the original species, a new species has evolved. Sympatric speciation occurs without ... | allenai/sciq |
Fossil evidence shows that amphibians evolved about 365 million years ago from a lobe-finned lungfish ancestor. As the earliest land vertebrates, they were highly successful. Some of them were much larger than today’s amphibians. For more than 100 million years, amphibians remained the dominant land vertebrates. Then s... | allenai/sciq |
Water is the main ingredient of many solutions. A solution is a mixture of two or more substances that has the same composition throughout. Some solutions are acids and some are bases. To understand acids and bases, you need to know more about pure water. In pure water (such as distilled water), a tiny fraction of wate... | allenai/sciq |
Giardia are flagellate protozoa that cause giardiasis . The parasites enter the body through food or water that has been contaminated by feces of infected people or animals. The protozoa attach to the lining of the host’s small intestine, where they prevent the host from fully absorbing nutrients. They may also cause d... | allenai/sciq |
Nucleic acids are one of four classes of biochemical compounds. (The other three classes are carbohydrates, proteins, and lipids. ) Nucleic acids include RNA (ribonucleic acid) as well as DNA (deoxyribonucleic acid). Both types of nucleic acids contain the elements carbon, hydrogen, oxygen, nitrogen, and phosphorus. | allenai/sciq |
12.5 Communication Between Neurons The basis of the electrical signal within a neuron is the action potential that propagates down the axon. For a neuron to generate an action potential, it needs to receive input from another source, either another neuron or a sensory stimulus. That input will result in opening ion cha... | allenai/sciq |
Streak is the color of the powder of a mineral. To do a streak test, you scrape the mineral across an unglazed porcelain plate. The plate is harder than many minerals, causing the minerals to leave a streak of powder on the plate. The color of the streak often differs from the color of the larger mineral sample, as Fig... | allenai/sciq |
The outer ear catches sound waves and funnels them to the middle ear. The middle ear amplifies the sound waves and passes them to the inner ear. The inner ear changes the sound waves to electrical signals. The signals travel to the brain, which interprets the sounds. | allenai/sciq |
22.1 Introduction Viruses are the smallest biological particle (the tiniest are only 20 nm in diameter). However, they are not biological organisms so they are not classified in any kingdom of living things. They do not have any organelles and cannot respire or perform metabolic functions. Viruses are merely strands of... | allenai/sciq |
Hot lower mantle material rises upward ( Figure below ). As it rises, it cools. At the top of the mantle it moves horizontally. Over time it becomes cool and dense enough that it sinks. Back at the bottom of the mantle, it travels horizontally. Eventually the material gets to the location where warm mantle material is ... | allenai/sciq |
A tissue is a group of connected cells that have a similar function within an organism. More complex organisms such as jellyfish, coral, and sea anemones have a tissue level of organization. For example, jellyfish have tissues that have separate protective, digestive, and sensory functions. | allenai/sciq |
As stated earlier, not all atoms of a given element are identical. Specifically, the number of neutrons in the nucleus can vary for many elements. As an example, naturally occurring carbon exists in three forms, which are illustrated in Figure below . | allenai/sciq |
Water is recycled constantly through the ecosystem. That means any water you drank today has been around for millions of years. You could be drinking water that was once drunk by George Washington, the first humans, or even the dinosaurs. | allenai/sciq |
The process in which organ systems work to maintain a stable internal environment is called homeostasis . Keeping a stable internal environment requires constant adjustments. Here are just three of the many ways that human organ systems help the body maintain homeostasis:. | allenai/sciq |
Figure below shows a diagram of Mercury’s interior. Mercury is one of the densest planets. Scientists think that the interior contains a large core made mostly of melted iron. Mercury's core takes up about 42% of the planet's volume. Mercury's highly cratered surface is evidence that Mercury is not geologically active. | allenai/sciq |
The sun and other stars consist of plasma. Plasma is also found naturally in lightning and the northern and southern lights. Human-made plasma is found in fluorescent lights, plasma TV screens, and plasma spheres. | allenai/sciq |
Most prokaryotes have a peptidoglycan cell wall and many have a polysaccharide capsule (Figure 4.5). The cell wall acts as an extra layer of protection, helps the cell maintain its shape, and prevents dehydration. The capsule enables the cell to attach to surfaces in its environment. Some prokaryotes have flagella, pil... | allenai/sciq |
There are very few living species of monotremes, or egg-laying mammals. They include the echidna and platypus, both pictured in Figure below . Monotremes are found only in Australia and the nearby island of New Guinea. | allenai/sciq |
The genetic code is the same in all living things. This shows that all organisms are related by descent from a common ancestor. | allenai/sciq |
Figure 15.2 All animals that derive energy from food are heterotrophs. The (a) black bear is an omnivore, eating both plants and animals. The (b) heartworm Dirofilaria immitis is a parasite that derives energy from its hosts. It spends its larval stage in mosquitos and its adult stage infesting the hearts of dogs and o... | allenai/sciq |
Through the process of transformation, the human gene for insulin is placed into bacteria. The bacteria then use that gene to make a protein. The protein can be separated from the bacteria and then used to treat patients. The mass production of insulin by bacteria made this medicine much more affordable. | allenai/sciq |
Mutualism is a symbiotic relationship in which both species benefit. An example of mutualism involves goby fish and shrimp (see Figure below ). The nearly blind shrimp and the fish spend most of their time together. The shrimp maintains a burrow in the sand in which both the fish and shrimp live. When a predator comes ... | allenai/sciq |
Longer chains of monosaccharides are referred to as polysaccharides . Starch, glycogen, and cellulose are three extremely common polysaccharides made entirely out of glucose molecules. The differences lie in the types of bonds between the glucose units and the extent of branching in the carbohydrate chain. Starch is fo... | allenai/sciq |
This equation is based on the conservation of energy and conservation of charge. Electrical potential energy can be described by the equation PE = qV , where q is the electric charge and V is the voltage. Thus the energy supplied by the source is qV , while that dissipated by the resistors is. | allenai/sciq |
Scientific theories are broad explanations that are widely accepted as true. This is because they are supported by a great deal of evidence. | allenai/sciq |
Warmer, lighter air is more buoyant than the cooler air above it. So the warm air rises. The cooler air is denser than the air beneath it. So it sinks down. This is convection: warm air rises, and cool air sinks. Warm fluids can undergo convection as well. This is described in the chapter Plate Tectonics . | allenai/sciq |
10.3 Dynamics of Rotational Motion: Rotational Inertia If you have ever spun a bike wheel or pushed a merry-go-round, you know that force is needed to change angular velocity as seen in Figure 10.10. In fact, your intuition is reliable in predicting many of the factors that are involved. For example, we know that a doo... | allenai/sciq |
The kinetic-molecular theory as it applies to gases has five basic assumptions. | allenai/sciq |
Cellular respiration and photosynthesis are direct opposite reactions. Energy from the sun enters a plant and is converted into glucose during photosynthesis. Some of the energy is used to make ATP in the mitochondria during cellular respiration, and some is lost to the environment as heat. | allenai/sciq |
where R can be an alkyl group, an aryl group, or a hydrogen atom. The simplest example, HCO2H, is formic acid, so called because it is found in the secretions of stinging ants (from the Latin formica, meaning “ant”). Another example is acetic acid(CH3CO2H), which is found in vinegar. Like many acids, carboxylic acids t... | allenai/sciq |
After tissues, organs are the next level of organization of the human body. An organ is a structure that consists of two or more types of tissues that work together to do the same job. Examples of human organs include the brain, heart, lungs, skin, and kidneys. Human organs are organized into organ systems, many of whi... | allenai/sciq |
Many amino acids can be linked together to form a long chain known as a protein . These linkages are formed when the carboxylic acid of one amino acid reacts with the amine of another to produce an amide (see Figure below ). | allenai/sciq |
A related process to diffusion is the effusion. Effusion is the process of a confined gas escaping through a tiny hole in its container. Effusion can be observed by the fact that a helium-filled balloon will stop floating and sink to the floor after a day or so. This is because the helium gas effuses through tiny pores... | allenai/sciq |
25.9 Regulation of Fluid Volume and Composition The major hormones regulating body fluids are ADH, aldosterone and ANH. Progesterone is similar in structure to aldosterone and can bind to and weakly stimulate aldosterone receptors, providing a similar but diminished response. Blood pressure is a reflection of blood vol... | allenai/sciq |
Oxides As with the halides, the nature of bonding in oxides of the transition elements is determined by the oxidation state of the metal. Oxides with low oxidation states tend to be more ionic, whereas those with higher oxidation states are more covalent. These variations in bonding are because the electronegativities ... | allenai/sciq |
There are four known types of bosons, which are force-carrying particles. Each of these bosons carries a different fundamental force between interacting particles. In addition, there is a particle which may exist, called the "Higgs Boson", which gives objects the masses they have. Some types of bosons have mass; others... | allenai/sciq |
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