Biology: Content Knowledge (5235) — ***

Which of the following is most likely to occur when double-stranded DNA is heated in the laboratory as part of the polymerase chain reaction (PCR) technique?

C.The DNA will separate into two strands as the hydrogen bonds are broken. Option (C) is correct. DNA must be heated during each cycle of PCR to break the hydrogen bonds holding the two strands together. The temperature of the reaction is then reduced so that added oligonucleotide primers can anneal by the formation of hydrogen bonds with the sequences to which they are complementary.

A study measuring the effect of drug Q on stomach pH was conducted on 120 individuals. An additional 120 individuals received a saline solution instead of drug Q. The averaged data are shown in the figure above. All individuals were given equivalent dosages at the start of the study. After 6 hours, how many times lower is the average proton (H+) concentration in individuals treated with drug Q than in individuals treated with saline?

D.1,000 Option (D) is correct. After 6 hours of treatment, the average stomach pH of the individuals treated with saline is 2, and the average stomach pH of the individuals treated with drug Qis 5. Every pH change of 1 represents a 10-fold difference in proton (H+) concentration. Hence, an increase of 3 pH units in the presence of drug Q represents a 1,000-fold lower proton (H+) concentration.

The DNA for the coding sequence of a gene that codes for a polypeptide containing 120 amino acids contains a minimum of how many nucleotide base pairs?

D.360 Option (D) is correct. Three sequential nucleotides in a molecule of mRNA code for each amino acid. If the polypeptide contains 120 amino acids, then 360 nucleotide base pairs (120 × 3) encode the coding sequence of the polypeptide.

Which of the following is associated with pioneer species?

D.Primary succession Option (D) is correct. Pioneer species are the first species to appear after a severe disturbance, such as a volcanic eruption accompanied by lava flow, removes all existing vegetation from an ecosystem. Because the soil is nutrient-poor, lichens and mosses or hardy plants with extensive root systems are common pioneer species.

Which of the following is true about all of the animals listed above?

D.They migrate. Option (D) is correct. All the animals do not share any one physical or metabolic characteristic in the options, but they do all share the behavior of migration.

Which of the following amino acids can contribute to the three-dimensional structure of a protein by forming covalent bonds with an identical amino acid in another part of the protein?

The picture with ( SH) in it Option (B) is correct. The amino acid represented in (B) is cysteine. Covalent disulfide bonds that form between the sulfhydryl (-SH) groups of cysteines in different parts of a protein are very important in determining the three-dimensional shape of the protein.

Exergonic and endergonic reactions in cells are interrelated in that

A.energy released from exergonic reactions can be used to power endergonic reactions Option (A) is correct. Many reactions in cells are energetically coupled. Energy released during an exergonic reaction is often equal to or greater than the amount of energy required for a simultaneous or sequential endergonic reaction to occur.

The role of denitrifying bacteria in the nitrogen cycle is to

B.convert nitrate, NO3-, to atmospheric nitrogen, N2 Option (B) is correct. Plants primarily acquire nitrogen in the form of NO3- that is formed in the soil by nitrifying bacteria. Denitrifying bacteria are facultative anaerobes that generally live deep in the soil or in stagnant water and return nitrogen to the atmosphere by converting nitrogen oxides to atmospheric nitrogen, N2.

Special infoldings are present on the respiratory surfaces of most terrestrial animals. This adaptation is useful because

B.gas exchange requires a thin, moist membrane of sufficient surface area to meet the requirements of the animal Option (B) is correct. Infoldings provide a greater surface area for the diffusion of O2 and CO2. The surface must be moist because gaseous oxygen molecules cannot pass directly through a lipid membrane such as the plasma membrane of cells. Instead, they must first dissolve in water. Examples of respiratory structures of terrestrial animals include the tracheal system of insects and the alveoli of mammals.

The skeletal structures of the human arm and whale flipper (pectoral fin) are shown above. The arm and flipper are examples of

B.homologous structures Option (B) is correct. Descent with modification is evident between species within a taxonomic category. Comparative anatomy (e.g., comparing skeletal structures) provides evidence of this. Similarity in characteristics between species because the species share a common ancestor is known as homology.

The diagram above shows the relationship between the anterior pituitary gland, thyroid-stimulating hormone, the thyroid gland, and thyroxine. An increase in the amount of thyroxine causes a decrease in the production of thyroid-stimulating hormone. This biological process is called

B.negative feedback Option (B) is correct. This is an example of negative feedback that maintains homeostasis in an organism. Thyroid hormones including thyroxine stimulate an increased rate of cellular metabolism. To keep the rate of metabolism relatively constant, thyroid hormones bind to the anterior pituitary gland to block release of thyroid-stimulating hormone until thyroid hormone levels drop.

The "beads on a string" analogy used to describe the structure of chromosomes refers to DNA-histone protein complexes called

B.nucleosomes Option (B) is correct. The nucleosome is the most basic unit of DNA packing in eukaryotic cells. A nucleosome consists of approximately 147 base pairs of DNA wrapped twice around an octamer of histones; a linker sequence of approximately 53 base pairs of DNA connects nucleosomes. This gives the appearance of beads on a string in electron micrographs.

Which of the following is a correct practice when using a light microscope?

D.A specimen on a slide should be located and brought into focus by first viewing it with a low-power objective. Option (D) is correct. It is far easier to find a specimen under low power because a larger portion of the slide is visible. It is also easiest to bring a specimen into focus under low power, and this is done primarily by using the coarse adjustment knob.

Which of the following will most likely disrupt the existing Hardy-Weinberg equilibrium in a very large population of rodents?

D.All females of reproductive age prefer to mate with males with long, bushy tails. Option (D) is correct. One of the conditions of Hardy-Weinberg equilibrium is that mating is random. If females preferentially mate with certain males, random mixing of gametes will not occur in the population, and genotype frequencies will change.

The stomach enzyme pepsin functions best in a narrow range of high hydrogen ion concentrations. Which of the following graphs represents the relationship between optimal pepsin enzyme activity and pH?

Option (C) is correct. The question states that pepsin functions best in a narrow range of high hydrogen ion concentrations. At pH 2.0, the hydrogen ion (H+) concentration is very high, which limits the choices to (A) or (C). (C) shows a peak of pepsin activity at pH 2.0.

The graph above depicts the changes in free energy (▵G)(▵G)⁢in a reaction without an enzyme. Which of the following graphs reflects the changes in free energy that will occur when an enzyme specific for the reaction is added?

The graph where it curves up and curves down Option (D) is correct. Enzymes are biological catalysts that change the rates of chemical reactions. Enzymes reduce the free energy of activation, or activation energy (EA)(EA), in a reaction without altering the free energy change for the reaction and hence allow reactions to proceed more rapidly.

The ecological role that an organism plays in the community is known as which of the following?

B.Niche Option (B) is correct. The sum of an organism's use of both abiotic and biotic factors in its community is referred to as the organism's ecological niche.

Reproduction by binary fission occurs in which of the following?

A.Bacteria Option (A) is correct. Bacteria divide by binary fission. A bacterium replicates its single chromosome, the two chromosomes become isolated at opposite poles of the cell, the bacterium enlarges, and then growth of new cell wall divides the single bacterium into two bacteria.

An individual with the genotype AabbccDd mates with an individual with the genotype AabbCCDd. Which of the following is the expected frequency of offspring with the genotype AaBbCcDd ?

A.0 Option (A) is correct. A rapid examination of the parental genotypes shows that it is unnecessary to perform any calculations. If the parental alleles at the B/b locus are each bb, none of the offspring can have a genotype of Bb at this locus.

Given the DNA sequence 5' ATGCCCTCA 3', which of the following is the correct complementary sequence of messenger RNA?

A.3' U A C G G G A G U 5' Option (A) is correct. A strand of messenger RNA has a base sequence complementary to that of the DNA template strand, and the strand orientations are antiparallel. The only difference between DNA-DNA and DNA-RNA pairing is that uracil in RNA replaces thymine in DNA.

Which of the following best describes the relationship between populations and communities?

A.A community is composed of populations. Option (A) is correct. A population is defined as the members of a single species in an area. The populations of the different species in an area make up the community.

Which of the following graph types should be used to illustrate the percent of hospital-acquired infections (nosocomial infections) in patients that are caused by each of several different organisms in a single year?

A.A pie chart Option (A) is correct. Pie charts are circular graphs in which each sector illustrates a proportion of a whole. A pie chart best illustrates and allows comparison of the percent of all hospital-acquired infections that are caused by particular organisms.

A diploid organism has the genotype AaBbCc for three loci, each of which is located on a different chromosome. A normal gamete produced by this organism could have which of the following genotypes?

A.AbC Option (A) is correct. When gametes form, each gamete will contain one member of each pair of homologous chromosomes. Gene loci that are on different chromosomes (i.e., that are unlinked) will assort independently. Hence, a gamete from this organism will contain either an A allele or an a allele of the first gene locus, a B allele or a b allele of the second gene locus, and a C allele or a c allele of the third gene locus.

Which of the following is required to initiate transcription of a particular gene in eukaryotic cells?

A.An RNA polymerase associates with transcription factors bound to the gene's regulatory sequences. Option (A) is correct. In eukaryotic cells, an RNA polymerase cannot bind to a gene and initiate transcription until transcription factors have bound to the gene. Typically, cell-specific regulatory transcription factors bind to the enhancer sequences of a gene, which facilitates the binding of general basal transcription factors to the promoter sequence, and finally the binding of the RNA polymerase.

Which of the following processes is shown in the figure above?

A.Biological magnification Option (A) is correct. Biological magnification refers to the increase in concentration of a substance as it moves up the food chain. The substance is generally very slow or impossible to break down and accumulates in the tissues of an organism. A small amount may be present in each individual organism at low levels of a food chain, but organisms at higher levels of the food chain are likely to eat many of the organisms at lower levels and thus ingest a lot of the substance. DDT is a pesticide that is stored in the fat of animals and takes many years to break down. It was banned for agricultural use in the United States in 1972 after its harmful effects on wildlife and particularly on birds had been well documented.

Which of the following occurs in the stroma of chloroplasts?

A.CO2 is fixed into organic molecules.

Which TWO of the following are the best examples of allopatric speciation?

A.DNA sequence similarity suggests that the flightless cormorant found on the Galápagos Islands and the flighted cormorants on the mainland share a common ancestor. D.The Isthmus of Panama separates two very similar populations of fish, the Cortez rainbow wrasse in the eastern Pacific Ocean and the blue-headed wrasse in the western Atlantic Ocean. Options (A) and (D) are correct. Allopatric speciation occurs when populations of a single species become geographically separated from each other and ultimately evolve into separate species. The flightless cormorant and the flighted cormorant share a common mainland flighted ancestor, but populations became separated after some members of the ancestral species moved to the islands and lost the ability to fly back to the mainland, so that the two populations diverged into separate species. The two species of wrasse most likely share a common ancestor, populations of which were separated by the formation of the Isthmus of Panama.

Which of the following is an example of a density-independent factor that affects a population?

A.Drought Option (A) is correct. Drought is an example of a density-independent factor that affects a population because it can, for example, cause the poor growth or death of a population of plants without the original density of the plant population affecting the outcome.

Which TWO of the following are characteristics of triglycerides?

A.Each molecule is composed of fatty acids linked to glycerol. D.Triglycerides occur as both solids and liquids at room temperature. Options (A) and (D) are correct. A triglyceride is composed of three fatty acids linked to a glycerol backbone by ester bonds. If the fatty acids of a triglyceride are saturated (as in most animal fats), the triglyceride will be solid at room temperature. If most of the fatty acids of a triglyceride are unsaturated (as in plant and many fish oils), the triglyceride will be liquid at room temperature.

Which of the following scientific theories is supported by the fact that mitochondria are enclosed by a double membrane and possess their own DNA?

A.Endosymbiotic theory Option (A) is correct. The endosymbiotic theory suggests that mitochondria were aerobic heterotrophic prokaryotes that were ingested by ancestral eukaryotic cells and formed a symbiotic relationship with the eukaryotes. Some of these eukaryotes later ingested photosynthetic prokaryotes, the precursors of plastids such as chloroplasts. This explains the fact that both mitochondria and chloroplasts have a double-membrane boundary while other organelles have only a single-membrane boundary, that they can replicate independently of the cell, and that they have their own genetic material.

Male stickleback fish have a characteristic red belly coloration. To defend its territory, a male stickleback fish will attack other male sticklebacks or a model that has a red mark on its belly, even if the model does not look like a fish. Attacking a model that does not look like a fish is an example of which of the following?

A.Fixed action pattern Option (A) is correct. Fixed action patterns are a sequence of behaviors that are triggered by an external sensory stimulus and that are basically unchangeable. Male sticklebacks act aggressively toward anything that bears a red marking on its underside.

The release of carbon dioxide during the burning of fossil fuels has contributed to which of the following environmental problems?

A.Global warming Option (A) is correct. Human activities, particularly the burning of fossil fuels and cutting down of forests, have contributed to increased CO2 in Earth's atmosphere. Much of the solar radiation that strikes Earth is reflected back to space but greenhouse gases, especially water vapor, CO2, and to a lesser extent, methane and ozone, absorb infrared radiation emitted by Earth and reflect some of it back to warm the planet. The increase in CO2 has contributed to an increase in greenhouse gases, thereby causing an increase in reflected infrared radiation and thus an increase in temperature.

The use of recombinant DNA technology to create a vaccine for which of the following pathogens has provided the most widespread benefit to individuals in the United States?

A.Hepatitis B virus Option (A) is correct. The vaccine against the hepatitis B virus consists of the hepatitis B surface antigen (HBsAg), a protein from the viral envelope that surrounds the virus. The protein is expressed in and purified from yeast cells. In many countries, the first of a series of three immunizations with this vaccine is given to infants at birth.

Experiments were conducted to test the rate of transpiration in plants under different environmental conditions. The stem of a plant was cut. Tubing, attached at one end to a water-filled pipet, was placed over the cut end of the shoot. The tubing and pipet were clamped as shown in the diagram above. Measurements of the water level in the pipet were recorded every 15 minutes. The experimental setup was placed in a room with partial sunlight at 25ºC. Which of the following conditions would cause the most rapid lowering of the water level in the pipet?

A.Increasing the light intensity Option (A) is correct. Transpiration is the evaporation of water through stomata in plant leaves, which creates a negative pressure and causes water to be absorbed into the plant through the roots. In this setup, an increase in transpiration rate will be indicated by a decrease in water level in the pipet. Of the choices, only increasing the light intensity will increase the transpiration rate. Additional light will cause the stomata to open more fully so that additional CO2 can enter the leaves to allow an increase in photosynthesis. The increase in the size of the stomata will increase the rate of transpiration and will pull more water into the shoot to facilitate the light reactions of photosynthesis.

Molecular geneticists have created fruit varieties that will not ripen naturally, allowing the fruit to be shipped over long distances without being damaged. They do so by inactivating genes for the production of a hormone that causes the fruit to ripen. Which of the following practices will cause the fruit to ripen once it is received?

A.Introducing ethylene gas into shipping containers or storage rooms Option (A) is correct. Ripening in fruits and senescence (aging) are caused by the production and release of ethylene gas by the fruits. The reason that fruit ripens more quickly in a shipping container or a storage room is because the container or room prevents the escape of ethylene, concentrating it and speeding up the ripening process.

On Earth, which THREE of the following are major reservoirs of carbon?

A.Limestone B.Oceans C.Sediments of aquatic ecosystems Options (A), (B), and (C) are correct. Limestone, oceans, and sediments of aquatic ecosystems are all major reservoirs of carbon. Of these three, the oceans are the major reservoir of actively cycling carbon.

Which of the following is a greenhouse gas that is produced in abundance by livestock manure and that some farms are now burning to produce electricity?

A.Methane Option (A) is correct. Methane is a greenhouse gas that is an abundant by‑product of the breakdown of livestock manure by anaerobic bacteria. Some farms are now collecting the manure in tanks called digesters, adding anaerobic bacteria to the digesters, and burning the methane and other gases produced by the bacteria in engines that in turn run electrical generators.

Which of the following helps explain why the largest land animals living today are predominantly herbivores?

A.More energy is available at lower trophic levels. Option (A) is correct. Approximately 90% of the energy in any trophic level is lost as energy is passed to the next trophic level. Herbivores eat only a small percent of organisms at the producer level and use much of the energy they consume in respiration. Energy is also lost as heat generated during their metabolic processes and in feces. Similar losses occur at each trophic level. Insufficient energy, only about 1% of primary production, is available to support carnivores, hence limiting their size.

Which THREE of the following essential elements for plant growth are obtained primarily through the roots?

A.Nitrogen B.Magnesium D.Potassium Options (A), (B), and (D) are correct. Nitrogen, magnesium, and potassium are three essential elements for plant growth and are obtained from the growth medium through the roots of a plant.

Acid precipitation can best be decreased by reducing the amount released to the atmosphere of which of the following?

A.Nitrogen oxides Option (A) is correct. Nitrogen oxides and sulfur dioxide released to the atmosphere are the major gases that contribute to acid precipitation or "acid rain." The major human source of the gases is from the combustion of fossil fuels. The gases react with water, oxygen, and other chemicals in the atmosphere to form acidic compounds that can fall to the ground in wet weather. Reducing dependence on fossil fuels will decrease the concentration of the gases in the atmosphere.

Which of the following substances can cross a biological membrane by simple diffusion without the assistance of transport proteins or channels?

A.Oxygen, O2 Option (A) is correct. Substances that are small and uncharged (e.g., O2) can cross the membrane most easily. Substances that are larger or that are charged cannot cross without the aid of a transporter protein or transport channel.

Which of the following processes is associated with a net decrease of plasma membrane?

A.Phagocytosis of a bacterium by a macrophage Option (A) is correct. The macrophage loses plasma membrane when it ingests the bacterium in a vesicle, often called a phagosome, which is formed by plasma membrane. Lost membrane is replaced when intracellular vesicles fuse with the membrane.

The changes in turgor pressure that cause the stomata of leaves to open and close result primarily from the reversible uptake and loss of which of the following ions by the guard cells?

A.Potassium Option (A) is correct. Stomata open when guard cells actively take up K+ from neighboring epidermal cells. Water osmotically follows the K+ and the guard cells become turgid, causing the stomata to open. The stomata close when the loss of K+, followed by water, causes the guard cells to become flaccid.

Which THREE of the following are features of meiosis that are most likely to contribute to genetic variation in a species?

A.Segregation of homologous chromosome pairs at anaphase I B.Independent assortment of chromatids at anaphase II D.Exchange of DNA between homologous nonsister chromatids Options (A), (B), and (D) are correct. Events that occur during meiosis that contribute to genetic variation in a species include the random segregation of homologous chromosome pairs at anaphase I, the independent assortment of chromatids at anaphase II, and the exchange of DNA between homologous nonsister chromatids (crossing‑over) that initiates with synapsis of homologous chromosome pairs at prophase I.

The sciatic nerve from a frog was isolated and placed into a nerve chamber. A recording of an action potential was measured when the nerve was bathed in a solution that mimics the extracellular fluid typically surrounding a cell, and the nerve was stimulated. The recording is shown above. If the toxin TTX, a potent sodium-channel blocker, is added to the bathing solution and the nerve is stimulated using a stimulus of the same strength, what will be the most likely change in the action potential?

A.The action potential will not occur, because depolarization will not occur. Option (A) is correct. When a neuron is given a threshold stimulus, an action potential is generated. The initial depolarization of the membrane is caused by a rapid influx of sodium ions into the cell, which makes the intracellular charge positive. If the sodium channels in the neuronal membrane are blocked, sodium ions cannot enter the cell and the action potential cannot be generated.

Which of the following has provided the strongest evidence for the evolution of organisms?

A.The fossil record Option (A) is correct. The fossil record is based mainly on the sequence in which fossils have accumulated in sedimentary rock layers. The association of fossils with certain rock strata and the advent of radiometric dating techniques allow scientists to determine the age of the fossils they study. A comparison of the similarities and differences between fossils in different layers has provided much evidence for the evolution of organisms and was the major source of evidence before the use of other techniques, such as comparative embryology and molecular biology.

Which of the following describes a mechanism by which tumor-suppressor proteins prevent cells with DNA mutations from becoming cancer cells?

A.The interaction between cyclins and cyclin-dependent kinases is blocked, which halts cell division. Option (A) is correct. Progression of the cell cycle is dependent upon the interaction of two types of proteins, cyclins and cyclin-dependent kinases (CDKs). M or S cyclins increase in concentration, then bind to CDKs. This activates the CDKs to phosphorylate proteins that promote the M or S phases of the cell cycle. The role of tumor-suppressor proteins is to modulate the cell cycle so that abnormal cells do not divide. Some tumor-suppressor proteins act by causing the production of proteins that block the interaction of certain cyclins with the CDKs and thus halt cell cycle progression until the cells can correct the abnormality or else undergo apoptosis (programmed cell death).

The fact that mutations of different genes can block different steps of a single metabolic pathway best supports which of the following?

A.The one gene-one polypeptide hypothesis Option (A) is correct. If each mutation blocks a different step in a metabolic pathway, it appears that each mutation alters the activity of the enzyme that catalyzes that particular step. Because each mutation is in a different gene, it strongly suggests that each gene encodes a different enzyme. Enzymes are proteins composed of one or more polypeptides. Extensive research has proved that this hypothesis is correct.

Which of the following must take place for ecological succession to occur in a given area?

A.The organisms living there at a given time must alter the environment. Option (A) is correct. As succession continues, organic matter increases in the soil, which allows the environment to support a larger, more diverse group of organisms. Seeds blown from nearby regions or brought by animals will germinate, and grasses, shrubs, and trees may grow. Depending upon the location of the region, trees may eventually crowd out lower-growing plants that need more light.

Some species of pine trees are adapted to fires. Seeds are released after the cones are exposed to fire. Which of the following is an advantage of this strategy?

A.The seedlings will have less competition after the fire. Option (A) is correct. The fire-adapted pine trees typically release the seeds from the cones at a particular temperature. After a fire, the undergrowth is typically destroyed, opening up the ground habitat. Since the pine seedlings need full sun to grow, the release of seeds after a fire helps to ensure better survival of the seedlings.

In a germinating seedling, the shoot grows upward toward the light while the root grows downward into the soil. Which of the following correctly explains these phenomena?

A.The shoot exhibits positive phototropism; the root exhibits positive gravitropism. Option (A) is correct. Phototropism is the growth toward or away from light; gravitropism is growth toward or away from the force of gravity on Earth. Shoots exhibit positive phototropism, which allows the photosynthetic leaves and stems to gain access to the sunlight. Roots exhibit positive gravitropism, growing down into the soil to gain access to water and to provide anchoring for the plant.

Which of the following is true about nonvascular plants, such as mosses?

A.The sporophyte is dependent on the gametophyte for nutrients and water. Option (A) is correct. In nonvascular plants, the gametophyte is the dominant form of the plant, and the sporophyte remains attached to the parent gametophyte and depends on the gametophyte for nutrients and water. This contrasts with vascular plants, where the sporophyte is the dominant form of the plant. In gymnosperms and angiosperms the gametophyte is dependent on the sporophyte for protection and nutrients.

When caribou migrate, the weaker ones often become the prey of wolves and other carnivores. If the vegetation that the caribou eat is sparse for several consecutive years, which of the following will most likely be true about the wolf population during that same period?

A.The wolf population will initially increase because of an increase in the wolves' food availability. Option (A) is correct. In this example of interacting organisms in a community, the caribou population will weaken because of lack of food, making them easier prey for the wolves. With the increase in food, more wolves will survive and hence will produce more offspring. With time, if the caribou population does not rebound, the number of wolves will also decrease.

Which TWO of the following features distinguish viruses from prokaryotes and eukaryotes?

A.Viral genomes are composed of DNA or RNA C.Viral proteins are synthesized only by an infected host cell. Options (A) and (C) are correct. Viral genomes are composed of DNA or RNA, in contrast to the genomes of prokaryotes and eukaryotes that are always composed of DNA. Viruses do not contain ribosomes or any materials required for translation and cannot synthesize their own proteins, in contrast to prokaryotes and eukaryotes that synthesize their own proteins.

Which of the following best describes a difference between viruses and prions?

A.Viruses contain nucleic acid, but prions do not. Option (A) is correct. A virus consists of a nucleic acid genome (either DNA or RNA) surrounded by a protein capsid. In some instances, the capsid is surrounded by another layer, the envelope, that is derived from cell plasma membrane. A prion is simply a protein that is misfolded and that triggers the misfolding of other similar proteins with which it interacts.

In the blood and tissue fluids, cholesterol is typically found in complexes with low-density lipoproteins (LDLs). Cells take up cholesterol when LDL receptors in the plasma membrane bind to the circulating cholesterol-LDL complexes. Cells do not take up cholesterol when there is an excess of free intracellular cholesterol. Which of the following is an example of a negative feedback mechanism by which cells can regulate the concentration of intracellular cholesterol?

A.When there is an excess of intracellular cholesterol, cells do not transcribe the gene encoding the LDL receptor. Option (A) is correct. A negative feedback mechanism is one in which the end result of a process negatively regulates the process to maintain stable conditions. If cells contain more cholesterol than required, then negative feedback blocks the cells from taking up any more cholesterol. The cells limit the amount of LDL receptor on the membrane by not transcribing the gene for the receptor. With less LDL receptor on the plasma membrane, fewer LDL-cholesterol complexes are taken up by the cells.

In flowering plants, the seed leaves that may store carbohydrates for the embryonic plant are called

A.cotyledons Option (A) is correct. A cotyledon is a part of the plant embryo that typically becomes the first leaf of the seedling. However, cotyledons are not true leaves and are derived differently. Flowering plants have either one cotyledon (monocots) or two cotyledons (eudicots). Cotyledons are found in gymnosperms as well.

A child is born to a man who has red‑green color blindness and a woman who has full color vision, whose father had red‑green color blindness. Red‑green color blindness is an X‑linked recessive trait. The chance that the child is a carrier of red‑green color blindness is

B.25% Option (B) is correct. A carrier of a recessive trait must have one wild‑type allele and one allele for the recessive trait, so the carrier of a recessive X‑linked trait such as red‑green color blindness can only be a female. Because the sex chromosomes of a man include one X and one Y chromosome, there is a 50% chance that the gamete from the man will contain the X chromosome, and the X chromosome will have the allele for red‑green color blindness. One of the two X chromosomes of the woman must have the allele for red‑green color blindness because she has full color vision, but the X chromosome she inherited from her father has the allele for red‑green color blindness. Thus there is a 50% chance that the gamete from the woman will contain an X chromosome with the allele for red‑green color blindness. Therefore, there is a 25% (0.5 × 0.5) chance that the child will be a girl with one of her two X chromosomes bearing the allele for red‑green color blindness.

Which of the following statements about the stratospheric ozone layer is accurate?

B.Accumulation of chlorofluorocarbons (CFCs) in the atmosphere has led to depletion of the ozone layer. Option (B) is correct. Liberation of chlorine atoms from CFCs has been a major factor in the formation of the ozone hole above Antarctica and the thinning of the ozone layer around the globe. Very little chlorine exists naturally in the atmosphere. Ultraviolet radiation breaks down CFCs and releases chlorine. The chlorine atoms can remain in the atmosphere for decades, catalyzing the destruction of ozone molecules and causing an increase in the penetration of ultraviolet light through the atmosphere.

On a global level, which of the following account(s) for the greatest annual use of freshwater?

B.Agriculture Option (B) is correct. It is estimated that global agriculture consumes over 90% of all freshwater used annually.

Which of the following pairs of scientists used bacteriophages, which are composed of only DNA and protein, to demonstrate that DNA is the heritable macromolecule that carries genetic information?

B.Alfred Hershey and Martha Chase Option (B) is correct. Bacteriophages are viruses that reproduce by infecting bacteria. Hershey and Chase infected bacteria with bacteriophages in which either the protein coat or the DNA inside the protein coat was labeled with a radioisotope. The only radioisotope they detected inside the bacteria or in progeny phages was that associated with DNA. Hence, DNA entered the bacteria and protein did not, proving that DNA rather than protein carries heritable genetic information.

Which of the following is a true statement about the disposal of aluminum soda cans?

B.Aluminum cans should be recycled because processing of aluminum ore requires a lot of energy. Option (B) is correct. Aluminum is refined from bauxite in a process that requires a tremendous amount of energy and also releases a lot of CO2 into the atmosphere. Recycling aluminum cans saves energy, reduces CO2 emissions, and decreases the amount of waste entering landfills.

External fertilization is typically found in which of the following organisms?

B.Amphibians Option (B) is correct. Amphibians typically live in a moist or aquatic environment, and many reproduce by external fertilization. The female releases eggs into the environment, and the male, who often clasps the female to maintain proximity, simultaneously releases sperm that fertilize the eggs.

Which of the following best describes punctuated equilibrium?

B.Long periods of evolutionary stability are followed by periods of rapid speciation. Option (B) is correct. Punctuated equilibrium refers to the pattern of change in the fossil record of some species and is typically defined as long periods of evolutionary stability followed by short periods of rapid speciation.

Investigators have immunized a rabbit with Substance P. They are studying the effect of the immunization on production of anti-Substance P antibodies over a two-week period following the immunization. Which of the following is the best hypothesis for the experiment?

B.Antibody production by the rabbit in response to Substance P will increase over a two-week period. Option (B) is correct. This statement is the only one that is directed toward antibody production over the two-week period and that is specific enough to suggest an analysis. Antibody levels in blood can be determined several times over the two-week period after drawing small volumes of blood from the rabbit.

Aphids are small insects that rest on the stems and leaves of plants and insert their needlelike mouthpiece directly into the phloem of the plants. Which of the following is the primary reason that an aphid infestation will kill a plant?;./

B.Aphids deplete the sugars normally available for the plant. Option (B) is correct. Phloem transports the products of photosynthesis (sugars) to growing parts and storage areas of the plant. By removing the sap from the phloem, aphids reduce the nutrients available to the plant.

A study was conducted to examine the growth patterns of bacteria. Three strains of a single species of bacteria were studied: wild-type that can synthesize all amino acids, mutant Y that lacks the ability to synthesize methionine, and mutant Z that lacks the ability to synthesize tyrosine. Four experiments were conducted in which different strains of bacteria were incubated for one hour at 37°C in growth medium containing all the essential amino acids, then plated onto minimal-medium agar plates and incubated overnight. (Minimal medium lacks amino acids but contains everything else that bacteria need to grow.) The results of the four experiments are shown in the table above.Which of the following mechanisms best explains the presence of colonies on the plates in experiment 4 ?

B.Conjugation Option (B) is correct. Conjugation is the direct transfer of genetic material between bacterial cells. Genetic recombination in these cells can lead to new strains of bacteria. In this case, mutant Y and Z strains transferred genetic material that was lacking in the strains independently. The recipients of the transferred DNA can now synthesize both methionine and tyrosine and survive to form colonies on the minimal medium.

Which of the following cell types are most likely to have motile cilia on the surface?

B.Epithelial cells lining the mammalian trachea Option (B) is correct. The ciliated epithelial cells that line the trachea are covered with a thin layer of mucus. Dust and other materials that enter the respiratory tract become trapped in the mucus. The beating of the cilia on the surface of the cells moves the mucus to the pharynx, where it can be swallowed, removing the materials. Each spermatozoon has a single flagellum, and no cilia are found on bacteria or fungi.

Which TWO of the following are scientific theories?

B.Evolutionary adaptations arise by natural selection. D.The number of species in an isolated island-like habitat is determined by an equilibrium between the rates of immigration and extinction.

Wind turbines are used for which of the following activities?

B.Generating electricity without burning fossil fuels Option (B) is correct. Wind turbines harvest a renewable resource, the wind, to produce electricity without the necessity of burning fossil fuels, a nonrenewable resource.

A volcano erupts, killing 87 percent of the members of a wildflower population. The original population had approximately equal numbers of pink and white flowering plants. Several generations after the eruption, only pink flowering plants are present in the population. Which of the following led to microevolution in this case?

B.Genetic drift Option (B) is correct. When natural disasters (e.g., earthquakes, fires, floods) kill large numbers of the population regardless of their fitness level, the allele frequencies in the remaining population are unlikely to be identical to those of the original population. This situation is known as the bottleneck effect and microevolution occurs. The bottleneck effect is one type of genetic drift.

In the food web shown above, which of the following groups of organisms includes fungi and bacteria?

B.Group R Option (B) is correct. Organisms in group R are decomposers and include fungi and bacteria. Organisms in group P are producers, and organisms in groups U, Q, S, and T are consumers. Decomposers are important recyclers of the energy and matter in ecosystems.

In individuals with a particular neurodegenerative disorder, physical and behavioral symptoms first appear when the individuals are in their 30s or 40s. The disorder is inherited in an autosomal dominant fashion and is caused by a particular gene with an excessive number of repeats of the trinucleotide sequence CAG. The disorder is most likely which of the following?

B.Huntington's disease Option (B) is correct. Huntington's disease is caused by an excessive number of repeats of the codon CAG (encodes the amino acid glutamine) in the Huntingtin gene (HTT). The severity of the disease and the age of onset correlate with the number of CAG repeats. If a parent passes an allele of the HTT gene with a large number of CAG repeats to a child, the child will develop the disease even if the allele inherited from the other parent has few CAG repeats. The mutated protein produced from an HTT gene with an excessive number of repeats is toxic to cells, particularly to brain neurons. Death of the neurons leads to movement, cognitive, and psychiatric disorders.

Ether may be used for anaesthetizing fruit flies for genetic experiments. The fruit flies are typically anesthetized in an etherizer, a small chamber that contains an absorbent material onto which a few drops of ether are placed before introduction of the flies. Ether is volatile and highly flammable. In which of the following locations should the ether be added to the etherizer?

B.In a fume hood, where the ether fumes are drawn to the outside of the building through an exhaust system Option (B) is correct. Fume hoods are typically designed so that air is drawn in from the front of the hood and exhausted to the outside or filtered before recirculation back into the hood. With correct use of the hood, neither the individual removing a few drops of ether from the bottle nor anyone else in the lab will be exposed to the ether fumes.

Which of the following describes the primary function of bone marrow in humans?

B.It is the source of new blood cells. Option (B) is correct. Hematopoiesis, the formation of all cells of the blood, occurs in the bone marrow. Pluripotent stem cells divide to produce new stem cells but also give rise to red blood cells, all types of white blood cells including lymphocytes and monocytes, and cells that are precursors to platelets.

Which TWO of the following processes occur as part of DNA replication?

B.One new strand is synthesized continuously, and one new strand is synthesized as a series of Okazaki fragments. C.A polymerase synthesizes RNA primers. Options (B) and (C) are correct. Because the two strands of a DNA molecule run antiparallel to each other, and because a single polymerase simultaneously adds nucleotides to the 3' ends of each of the two new strands, one new strand of DNA is synthesized in a continuous fashion, and the other new strand is synthesized in a discontinuous fashion in a series of Okazaki fragments that are ligated together after synthesis. DNA polymerases can only add nucleotides to a preexisting 3' end, but RNA polymerases do not have this requirement. Thus an RNA polymerase lays down an RNA primer with an available 3' end to which the DNA polymerase can attach deoxynucleotides (dNTPs) for the start of both continuous synthesis and the synthesis of each Okazaki fragment. Another DNA polymerase later replaces the RNA primers with dNTPs.

Which of the following will best help maintain the diversity and abundance of organisms in a terrestrial ecosystem?

B.Preventing habitat destruction Option (B) is correct. The single greatest threat to loss of both terrestrial and aquatic biodiversity is habitat destruction by humans. Associated with habitat loss is habitat fragmentation, in which organisms are forced to occupy much smaller regions that are more sensitive to environmental changes and where the organisms face a much greater chance of extinction.

An isolated hillside in a temperate deciduous forest was used for an ecological study. The hillside was treated with defoliant and herbicides for one year. The dead organic matter was left to decay at the site. Which of the following statements most reflects what changes can be expected in the hillside forest environment?

B.Secondary succession will occur. Option (B) is correct. Although an increase in erosion and water runoff will deplete the soil of nutrients, once the defoliant and herbicide treatment cease, succession will occur. In this setting, succession will more than likely return the area to its original state.

In a particular ecosystem, the number of bobcats has been approximately the same for the past ten years. Which of the following best explains why the number of bobcats has not changed significantly over the ten-year period?

B.The bobcat population is at carrying capacity. Option (B) is correct. Carrying capacity is the maximum number of individuals that an environment can support indefinitely given the available food, water, nesting sites, etc. These factors are called limiting factors, as it is their availability that determines how many individuals can be supported. Each species in an ecosystem is subject to limiting factors.

Enzyme X catalyzes digestion of bacterial cell walls, resulting in lysis of the bacteria. A solution of enzyme X was prepared and equally divided into five test tubes. The pH of the solution in each tube was then adjusted, and an equal volume of a bacterial stock solution was added to each of the five tubes. After 10 minutes of incubation at 37°C, each tube was placed in a spectrophotometer, and the percent of light transmitted was recorded as shown in the table above. Which of the following is the dependent variable in the experiment?

B.The catalytic activity of the enzyme Option (B) is correct. The dependent variable is the variable that changes in response to a change in the independent variable. In this scenario the catalytic activity of the enzyme changes in response to the adjusted pH of the enzyme X solution.

Epithelial cells of the small intestine have folds called microvilli on the surface that faces the interior of the intestinal tract. Which of the following best describes the role of the microvilli?

B.The folds increase the rate of nutrient absorption by the cells. Option (B) is correct. The smooth intestine is specialized for absorption of nutrients from digested foods. A common motif in cells and organelles in which maximizing surface area is important for a particular process is the presence of folds in the membrane.

Which of the following characteristics of a material found on the bark of a tree will most likely prove that the material is a living thing?

B.The material appears to reproduce on its own. Option (B) is correct. One of the characteristics of a living thing is that it can reproduce on its own.

Scientists have proposed that echinoderms and chordates form a monophyletic group because they share a recent common ancestor. Which of the following evidence best supports this proposal?

B.The two groups have similar patterns of embryonic development. Option (B) is correct. Based on certain aspects of embryonic development, many organisms can be classified by following one of two developmental modes: protostome development or deuterostome development. Both echinoderms and chordates exhibit deuterostome development, in which the opening that develops during gastrulation (the blastopore) becomes the anus, as opposed to protostome development, in which it becomes the mouth. The presence of three germ layers is found in both deuterostomes and most protostomes, as is segmentation. Typically, protostomes show spiral cleavage and deuterostomes show radial cleavage.

Which of the following statements is true about the inheritance of color blindness in the family represented in the pedigree above?

B.There is a 50% chance that individual 3 will express the trait of color blindness. Option (B) is correct. Color blindness is an X-linked recessive trait. Because males have only one X chromosome, a male who inherits an X chromosome from his mother that carries an allele for color blindness will be color blind. A female will only be color blind if she inherits X chromosomes from both parents that carry the allele for color blindness. Individual 3 is a female who inherits an X chromosome from her father that carries the color blind allele. She has a 50% chance of inheriting the color blind allele from her carrier mother and thus a 50% chance that she will be color blind.

Which of the following structures pumps blood out of the mammalian heart?

B.Ventricle Option (B) is correct. Blood returning to the heart enters the atria, passes through valves into the ventricles, and is pumped out by the ventricles. The right ventricle pumps blood to the lungs, and the left ventricle pumps blood to the rest of body.

In an attempt to understand human diversity, scientists are studying slight variations in individual DNA sequences from people around the world. This type of research is known as

B.bioinformatics Option (B) is correct. Bioinformatics is a multidisciplinary field that is heavily dependent on computer software tools, mathematics, and engineering for storing, analyzing, and retrieving biological data such as the sequences of DNA from many different sources.

Chlamydomonas reinhardtii is a unicellular green alga that has a diameter of approximately 10 microns. 10 microns is equivalent to

C. 0.01 mm Option (C) is correct. 1 micron ( μmμm) equals 10-6 m, 10-4 cm, and 10-3 mm. Hence, 10 microns equals 10-2 mm or .01 mm.

A mature ovum produced from division of a primary oocyte has 18 chromosomes. How many chromatids were present in the primary oocyte during prophase I of meiosis?

C. 72 Option (C) is correct. If a mature ovum contains 18 (n) chromosomes, then the primary oocyte contained 36 (2n) chromosomes. Each chromosome was composed of two identical chromatids immediately after DNA replication, which occurred before the primary oocyte entered prophase I of meiosis. Hence, 72 chromatids were present in the primary oocyte during prophase I.

Four percent of an isolated population suffers from an autosomal recessive genetic disease. Assuming the population is in Hardy-Weinberg equilibrium for the trait in question, what percent of the population are carriers?

C.32% Option (C) is correct. This question requires use of the Hardy-Weinberg equation to determine allele and genotype frequencies in a nonevolving population. The Hardy-Weinberg equation is p2+2pq+q2=1p2+2pq+q2=1, where p equals the frequency of the dominant allele and q equals the frequency of the recessive allele, and p + q = 1. Then p2 equals the frequency of individuals with a homozygous dominant genotype, q2 equals the frequency of individuals with a homozygous recessive genotype, and 2pq equals the frequency of heterozygotes in the population. The problem gives the value of q2 = 0.04. Thus q = 0.2 and p = 0.8. Therefore 2pq = 0.32, or 32%.

A certain animal species with specific habitat requirements is found in only a few small, isolated populations, which are located in protected wildlife preserves. Which of the following most likely poses the greatest threat to the species' long‑term survival?

C.A decrease in the genetic diversity of the populations Option (C) is correct. If a population has only a few members and is isolated from other populations, inbreeding will occur, and gene flow will not occur. The number of alleles of each gene will be limited in the population. If the population faces a threat such as a pathogen that targets members of the population with a specific phenotype, it is likely that much of the population will be wiped out because of the lack of genetic diversity and thus of phenotypic diversity.

A high school student is seeking background information for the discussion section of a lab report. Which of the following will provide the most reliable and current information?

C.A recent research paper in a scientific journal Option (C) is correct. Research papers that appear in scientific journals undergo extensive peer review before they are published. A recent research paper will be both current and reliable. The sources in the other options may provide information that is either unreliable or not current.

According to evolutionary theory, which of the following individuals has the greatest Darwinian fitness?

C.A woman who lives to be 80 years old, has 6 children and 30 grandchildren, and is in poor health most of her life Option (C) is correct. Darwinian fitness is largely defined by the ability to survive, reproduce, and pass on one's genes. Despite the fact that the woman is in poor health most of her life, she has more children than any of the other individuals has. Because she also has 30 grandchildren, the woman has made a large contribution to the gene pool of two generations.

Which of the following physiological responses helps to reduce body temperature?

C.Activation of the sweat glands Option (C) is correct. Sweat gland activation releases sweat onto the surface of the skin and allows for evaporative cooling. All the other responses lead to an increase in metabolic heat production and therefore raise the body temperature.

The concentration of a stock solution of sulfuric acid is 18 M. Of the following, which describes the correct way to prepare 500 mL of a 1 M solution of sulfuric acid?

C.Add 28 mL of the stock sulfuric acid to 400 mL of water, and add water to bring the total volume to 500 mL. Option (C) is correct. Concentrated acids are always diluted by adding the stock acid solution to water. If the stock solution of sulfuric acid is 18 M, it must be diluted 18‑fold to bring it to a 1 M concentration. 500 mL/18 is approximately 28 mL, so 28 mL of the 18 Mstock sulfuric acid is added to approximately 400 mL of water, and then the final volume of the solution is brought to 500 mL. 28 mL of acid is not added to 472 mL of water, in case the volume of the solution increases when the acid and water are mixed.

What was Antoni van Leeuwenhoek's major contribution to biology?

C.Advancing the field of microscopy through the discovery of bacteria and protists Option (C) is correct. Antoni van Leeuwenhoek designed his own optical lenses and microscopes in the seventeenth century and perfected his technique to such a degree that the magnification he achieved with his lenses was much greater than that of any lenses used by his contemporaries. He examined samples from a wide range of sources and was the first to describe single-celled organisms, protists and bacteria, as well as red blood cells and spermatozoa.

A researcher identifies a new species within the moist soil of a wooded area. The species exhibits bilateral symmetry, has internal body segmentation, and uses metanephridia to remove wastes from its blood and coelomic fluid. Based on these characteristics, the new species should be categorized in which of the following animal phyla?

C.Annelida Option (C) is correct. The characteristics exhibited by the new species are all features of the phylum Annelida (i.e., segmented worms).

Which of the following is a recommended safety practice in school biology labs?

C.Chemical-resistant gloves and aprons are recommended when performing dissections for protection against preservatives used in the specimens. Option (C) is correct. Many specimens are often initially preserved in formaldehyde or other toxic chemicals, although these chemicals are removed and replaced by safer ones before the specimens are shipped to schools. Chemical-resistant gloves and aprons are a good precaution against skin irritation and damage to clothes.

Which of the following best describes the role of buffers in living systems?

C.Combining with excess H+ and OH- ions in solution Option (C) is correct. A buffer minimizes changes in the concentration of H+ and OH- ions in a solution. An approximately neutral pH must be maintained in human blood and many other biological solutions. This is accomplished by buffers such as the carbonic acid-bicarbonate buffering system in the blood.

Which of the following biomes is correctly paired with the description of its characteristics?

C.Estuary: salt-marsh grasses, algae, and phytoplankton prevalent, variable water salinity Option (C) is correct. An estuary is an area where a freshwater stream or river merges with an ocean, causing variable salinity in the area. Major producers, including grasses, algae, and phytoplankton, support a wide variety of invertebrates and fish species.

The amino acid sequence of the same protein was evaluated in five different organisms. The table above shows, for each organism, the number of differences that were found between the protein and the human version of the protein. Which of the following statements is best supported by the data?

C.Humans and chimpanzees diverged genetically more recently than humans and snakes diverged. Option (C) is correct. As organisms diverge further from each other and evolve separately, the amino acid differences in shared proteins accumulate. The fact that the particular protein in humans differs by only one amino acid from the protein in chimpanzees but differs by 36 amino acids from the protein in snakes suggests a much more recent divergence of humans and chimpanzees than of humans and snakes.

Which of the following best explains why epidemiologists suggest that a certain percent of the population should be vaccinated against any given contagious pathogen?

C.If a sufficient number of people are vaccinated, unvaccinated people are less likely to encounter an infectious individual and become ill. Option (C) is correct. This refers to the concept known as herd immunity. Unvaccinated individuals are protected if enough of the population is vaccinated because an unvaccinated individual will rarely encounter an infectious individual who can transmit a pathogen.

Which of the following statements about the acrosome of a human sperm is correct?

C.It contains enzymes to help the sperm penetrate the egg. Option (C) is correct. The acrosome is located at the tip of the sperm head. In humans, the sperm binds to the zona pellucida around the egg, which triggers what is termed the "acrosome reaction" in the sperm. Enzymes are released by exocytosis from the acrosome that help the sperm tunnel through the zona pellucida. The sperm binds to the oocyte and fuses with the oocyte plasma membrane.

In a plant, undifferentiated cells that can divide throughout the life of the plant to enable growth are found in which of the following?

C.Meristem Option (C) is correct. The meristem consists of cells that remain undifferentiated and that enable the shoots and roots of the plant to grow in length and girth throughout the life of the plant.

Most cases of Tay‑Sachs disease are caused by which of the following?

C.Mutations in a gene encoding a particular lysosomal enzyme Option (C) is correct. Tay‑Sachs disease is generally caused by a mutation in a gene encoding a lysosomal enzyme that is required for breaking down a particular fatty material in neurons of the brain and spinal cord. As a result, this material accumulates in the lysosomes of the neurons, leading to the destruction of these cells and a progressive deterioration of the central nervous system.

Which of the following provides the immediate source of energy to establish the proton (H+) concentration gradient across the inner membrane of mitochondria during aerobic respiration?

C.Oxidation-reduction reactions as electrons are passed sequentially along members of the electron transport chain Option (C) is correct. The electron carriers NAD+ and FAD are reduced to NADH and FADH2, respectively, during glycolysis and the Krebs cycle (citric acid cycle). NADH and FADH2 are then oxidized with the simultaneous reduction of early members of the electron transport chain (ETC). A series of redox reactions occurs as the electrons are passed from one member of the ETC to the next member. Each sequential member of the ETC is slightly more electronegative than the previous member, so energy is released as the electrons are passed along, until the electrons ultimately reduce oxygen. The energy released enables three members of the electron transport chain to pump protons (H+) against their gradient across the inner membrane of the mitochondrion into the intermembrane space.

The crossover frequencies between four genes on a single chromosome are shown in the table above. Based on the data, which of the following is the most likely order of the four genes?

C.P N O M Option (C) is correct. Because the crossover frequency between genes O and P is 25%, gene O is probably further from gene P than is gene N that has a crossover frequency with gene P of 20%, but this does not indicate whether genes N and O are on the same side or different sides of gene P. The crossover frequencies of gene M with genes N and O provide this information. Because the crossover frequency between genes M and O (10%) is less than that between genes M and N (15%), gene O is most likely between genes N and M, and thus gene N is between gene P and gene O. Based on crossover frequencies, a map of the four genes is: P ‑ 20 mu ‑ N ‑ 5 mu ‑ O ‑ 10 mu ‑ M ("mu" represents map units).

A researcher collects what appears to be a new species in a freshwater stream. Microscopic analysis shows the presence of chloroplasts, mitochondria, a defined nucleus, and a cellulose-based cell wall. Individual cells cluster to form colonies, but the colony lacks any true tissue or organ formations. This new species most likely belongs in which of the following kingdoms?

C.Protista Option (C) is correct. The characteristics described are those of green algae, which are protists. Although many of the features are also common to members of kingdom Plantae, plants all possess some level of tissue specialization and features that allow their adaptation to a terrestrial environment. Of the kingdoms listed in the options, fungi also have cell walls, but their primary component is chitin rather than cellulose.

Gregor Mendel noticed that when he crossed two pea plants with tall stems, some of the offspring had short stems. Which of the following best explains his observation?

C.Segregation Option (C) is correct. Expression of tall pea plants is dominant to expression of short pea plants. The tall pea plants must have been heterozygous at the gene locus determining stem length. When gametes formed, the dominant and recessive alleles determining stem length segregated so that some gametes contained the allele for long stems and other gametes contained the allele for short stems.

Which of the following structures will most likely be damaged if there is an injury to the cells of the endoderm during embryogenesis?

C.Stomach lining Option (C) is correct. The endoderm layer gives rise to the epithelial lining of many organs and body systems, including the liver, pancreas, thyroid gland, urinary bladder, digestive tract, respiratory system, and the reproductive system.

Which of the following biomes is characterized by the presence of a distinct winter season, fertile soil with litter, and precipitation that is distributed throughout the year?

C.Temperate forest Option (C) is correct. Temperate forests can be distinguished from other biomes by having distinct seasons, including a winter season; leaf litter contributing to the soil; and rain throughout the year.

Of the following, which will be most important in ensuring the successful establishment of a new wildlife preserve or national park in a rural community?

C.The cooperation of individuals who live in the area or have been displaced by the park Option (C) is correct. To successfully establish a new wildlife park or national park in a rural community, it is important that individuals living in the area or displaced by the park are provided with new homes and/or livelihoods, possibly associated with the park, and understand the importance of the park. The individuals will be far more likely to cooperate and support the goals of the park if they are not negatively affected by its presence.

Which of the following is an example of postzygotic reproductive isolation?

C.The hybrid offspring of parents belonging to different equine species do not produce viable gametes. Option (C) is correct. Zygotes are fertilized eggs that can develop into mature organisms. Postzygotic reproductive isolation therefore refers to the inability of a hybrid zygote to develop to maturity or of a hybrid organism to produce viable offspring. If a hybrid organism produces eggs or sperm that are not viable, then the gene pools of the two species from which the hybrid was produced will remain distinct.

Which of the following contributes most to the ability of water to serve as a solvent for salts and many biological molecules?

C.The oxygen region of a water molecule has a partial negative charge, and the hydrogen regions have partial positive charges. Option (C) is correct. Because of the dipolar nature of water, water forms bonds with charged molecules or portions of molecules. Ions are typically surrounded by hydration shells of water in which the negative oxygen region of water molecules bonds with positively charged ions and the positive hydrogen regions of water molecules bond with negatively charged ions. Similarly, water molecules form bonds with charged regions of other molecules such as proteins and carbohydrates, and this keeps the molecules dissolved in aqueous solutions such as body fluids.

Many songbirds winter in one ecosystem and migrate to another to breed. Which of the following is most likely to occur if the habitat in the wintering grounds of a migratory songbird is degraded by human activity?

C.The population size of the birds will decrease as fewer birds will return to the breeding grounds. Option (C) is correct. Most migrating songbirds winter in warm locations that generally have good food supplies, and the birds depend on the supplies to survive the winter and the long trip back to the breeding grounds. If humans encroach on the wintering grounds, there is likely to be insufficient food, and the birds will be less able to survive the winter and make the long flight back to the breeding grounds. Therefore, fewer birds will return to breed, and there will be a reduction in population size.

Which of the following statements regarding the water cycle is correct?

C.The water cycle differs from other biogeochemical cycles because most water moves through ecosystems by physical rather than chemical processes. Option (C) is correct. On a global scale, net movement of water is from the oceans to the land. Evaporation exceeds precipitation over the oceans; precipitation exceeds evaporation over the land. In a land environment, precipitation returns water to the ground, where it either percolates through the soil to collect as groundwater or becomes surface runoff.

DNA samples from saliva collected at a crime scene were matched against DNA from two suspects and a bystander. The diagram above represents an agarose gel in which the products of amplification of the DNA samples have been separated by electrophoresis and stained for visualization. Band sizes are indicated to the left. Why was the bystander's DNA included in the study?

C.To control for contamination from the bystander's DNA Option (C) is correct. DNA fingerprints from unrelated individuals differ. It is important to eliminate those bands in a crime scene DNA fingerprint that are irrelevant because they represent contamination from bystanders. The remaining bands in the crime scene DNA fingerprint can then be compared with the DNA fingerprints of individual suspects.

An animal with three distinct body divisions, a pair of antennae, compound eyes, and six legs is most likely

C.an insect Option (C) is correct. The features described are all common to insects.

A difference between plants and fungi is that plants

C.are autotrophic Option (C) is correct. Plants are autotrophs that synthesize their own organic nutrients, sugars, by photosynthesis. Fungi are heterotrophs that absorb their organic nutrients from their surroundings.

In a particular multicellular organism, the cells are connected in long filaments called hyphae, the cell walls contain chitin, and the cells are often multinucleate. The organism is most likely a

C.fungus Option (C) is correct. Most fungi are capable of producing hyphae, cells of many types of fungi contain more than one nucleus, and the primary component of fungal cell walls is chitin.

A wild-type fruit fly that is heterozygous for both body color and eye color is mated with a fly exhibiting two recessive mutations, ebony body and sepia eyes. The offspring distribution is as shown in the table above. Based on the data, genes for ebony body and sepia eyes in fruit flies are most likely

C.linked Option (C) is correct. If two genes are on separate chromosomes (i.e., unlinked), random assortment during gamete formation would be expected to yield equal numbers of both parental type and recombinant type (in this instance, one wild trait and one mutant trait) offspring. If the genes are in close proximity (i.e., linked), crossing-over events lead to the formation of a smaller number of recombinant offspring than expected for unlinked genes. The data show that the frequency of recombinants is lower than that of the parental type offspring and that there is no discrepancy between the occurrence of recombinants in males and females.

The human karyotype above represents which of the following?

D.A female with a normal karyotype Option (D) is correct. A karyotype shows the quantity of each chromosome as well as any chromosomal abnormalities such as a missing piece. It also shows the sex of the individual. Because this individual appears to have a normal array of chromosomes, including two X chromosomes, the conclusion is that this is a female with a normal karyotype.

In photosynthesis, light energy is converted to chemical energy with an efficiency of approximately

D. 1% Option (D) is correct. Of the visible light that reaches photosynthetic organisms, only about 1% is of wavelengths that can be absorbed by the pigments of the organisms. The rest of the light is reflected, transmitted, or lost as heat.

Which of the following is considered to be a risk factor for developing type 2 diabetes, a disease typically characterized by the unresponsiveness of cells to insulin?

D.Being overweight Option (D) is correct. Individuals who are overweight are generally thought to be at higher risk for developing type 2 diabetes. Insulin binds to receptors on most body cells and induces the cells to take up glucose from the blood. Evidence exists that in individuals with more fatty tissue, body cells have fewer insulin receptors on their membranes, are thus less responsive to insulin, and take up less glucose from the blood.

Which of the following best accounts for the complex regulation of gene expression in multicellular eukaryotic species?

D.Cell- and tissue-specific gene expression Option (D) is correct. The genome is essentially identical in all nucleated cells of a particular multicellular organism. Regulation of gene expression is responsible for the wide variety of cell types present. Different genes have different enhancer sequences upstream of the coding region. For a gene to be expressed, the cell must contain regulatory transcription factors that can bind to the specific enhancer sequences. Different cells contain different regulatory transcription factors. Binding of the regulatory transcription factors allows the binding of generic (non-cell specific) basal transcription factors followed by the binding of RNA polymerase. If the cell does not contain regulatory transcription factors that bind a gene's enhancer sequence, the gene will not be expressed.

Which of the following organelles can synthesize some of its own proteins?

D.Chloroplast Option (D) is correct. Both chloroplasts and mitochondria contain DNA encoding some of their own proteins and also contain their own RNA polymerases and ribosomes. Hence, these organelles synthesize some of their constituent proteins.

Using DNA technology, researchers are engineering nitrogen-fixing bacteria that can live in the tissues of nitrogen-demanding plants, which would reduce the need to use chemical fertilizers. Which of the following crops would most likely benefit from this kind of research?

D.Corn Option (D) is correct. Nitrogen is the most limiting nutrient in corn production. The root nodules of all legumes, which include soybeans, alfalfa, and green beans, contain nitrogen-fixing bacteria that supply nitrogen to the plants. No such bacteria are associated with the roots of corn plants, so farmers generally turn to nitrogen-containing fertilizers.

Polymerase chain reaction (PCR) is a technique used to amplify small amounts of DNA for further study. Which of the following is (are) a key component used in PCR?

D.DNA primers Option (D) is correct. To amplify a specific region of DNA in a sample, DNA primers that are complementary to sequences flanking the region of interest are added to the reaction mixture. The reaction mixture is heated to denature the double-stranded DNA, and then cooled to allow annealing of the primers to the sample DNA. After the primers anneal, Taqpolymerase or another heat-stable DNA polymerase extends the DNA from the 3' end of each primer across the region of interest.

Which of the following is most likely to occur during prophase I of meiosis?

D.DNA-histone interactions cause a gradual increase in chromosome packing. Option (D) is correct. In eukaryotic cells, DNA is associated with histones, the complex of which is known as chromatin. Interactions between the DNA and the histone proteins lead to the formation of chromosome coils and loops. These coils and loops increase during prophase I to compact the chromosomes.

Which of the following environments will most likely experience the longest-lasting effects from a major hurricane?

D.Deciduous forest Option (D) is correct. Hurricanes typically have high winds and heavy rainfall. Of the environments listed, the one most likely to be affected by both wind and rain is the deciduous forest. The wind and rain contribute to fallen trees and flooding of rivers and streams that will affect many of the organisms inhabiting the forest.

Which of the following statements best describes the process shown in the diagram above?

D.Energy is stored in the form of ATP. Option (D) is correct. Hydrolysis of ATP provides the most immediate form of energy in cells. Breakdown of nutrients such as glucose takes significantly longer. Hence, glucose is broken down and the energy stored in the bonds of glucose is transferred to energy stored in the phosphate bonds of ATP. When a cell needs immediate energy to carry out a process, ATP is hydrolyzed to ADP + Pi .

Which of the following organisms is most likely to produce hundreds of eggs, of which only a few will become adult animals?

D.Frog Option (D) is correct. Female frogs generally release hundreds to thousands of eggs into water, where the eggs undergo external fertilization by sperm released by a male frog. Not all the eggs will be fertilized, and many of the fertilized eggs will be eaten by predators or otherwise destroyed, so only a few will develop into tadpoles. Finally, only a portion of the tadpoles will survive to undergo metamorphosis to frogs.

Behavioral biologist Konrad Lorenz noticed that baby geese considered him to be their mother if he was the first image they saw immediately upon hatching. The baby geese were exhibiting which of the following behaviors?

D.Imprinting Option (D) is correct. This is the classic example of imprinting. Imprinting refers to a long-lasting specific behavioral response to an individual or object that occurs when an organism is exposed to that individual or object at a certain developmental stage in that organism's life.

A horticulturist crosses two snapdragon plants that bear pink flowers. In addition to 83 pink-flowering plants, the offspring from the cross consist of 38 red-flowering plants and 40 white-flowering plants. Which of the following is the most likely mode of inheritance described above?

D.Incomplete dominance Option (D) is correct. This is a classic example of incomplete dominance in which the cross of two plants with an intermediate phenotype produces offspring in which about 50% have the intermediate phenotype and about 25% have each of the two phenotypes of the plants initially crossed to produce plants with the intermediate phenotype. A plant with only one copy of the allele for red pigment produces only enough pigment to be pink; two copies of the allele are required for the red color.

The most common objection expressed by some individuals in the United States to the medical use of human embryonic stem cells is which of the following?

D.Isolation of the cells requires destruction of embryos. Option (D) is correct. Human embryonic stem cells are derived from the inner cell mass of a blastocyst, a ball of 70-150 cells. Under the correct conditions, the cells can differentiate into every kind of cell in the body and hence have great potential for treating diseases. Their use, however, raises the ethical concern of whether an embryo should have all the rights of a human. Although most of the embryos from which stem cells are derived will never be implanted in a recipient, isolation of the cells means the death of an embryo that has the potential to develop into a human being.

Which of the following processes is most likely responsible for the recent increase of pathogenic bacteria that cannot be killed by commonly used antimicrobial drugs?

D.Natural selection Option (D) is correct. In every population of bacteria treated with an antimicrobial drug that specifically targets them, a small fraction of bacteria may have mutations that enable them to survive in the presence of the drug. The drug will eliminate all the susceptible bacteria and will select for those with the mutations. The drug is the agent of natural selection.

An insect species lays its eggs on a specific type of plant leaf. The leaves hide the insect eggs from predators and protect them from the environment. As the eggs hatch, the insect larvae feed on the leaves. Which of the following best describes the relationship between the insect and the plant?

D.Parasitism Option (D) is correct. In a parasitic relationship, one organism benefits while the other is harmed. In the relationship between the insect and plant, the insect is protected and gains nutrients from the plant, but the plant is damaged by the insect.

Which of the following typically triggers an increase in the respiratory rate of an individual during exercise?

D.Sensors in blood vessels and the medulla detect a decrease in the blood pH. Option (D) is correct. Exercise causes an increase in metabolic activity, and increased metabolic activity increases the concentration of CO2 in the blood and cerebrospinal fluid. The CO2 reacts with water in the blood and cerebrospinal fluid to form carbonic acid (H2CO3), which dissociates to a bicarbonate ion (HCO3-) and a proton (H+). The increased concentration of protons lowers the pH of the blood and cerebrospinal fluid, a decrease that is sensed by specialized cells in major blood vessels and neurons in the medulla.

A biologist reports the length of a captured snake as 105.030 cm. How many significant figures are in the measurement?

D.Six Option (D) is correct. The measurement 105.030 contains six significant figures. All nonzero numbers are significant, zeros between nonzero numbers are significant, and zeros to the right of the decimal point and at the end of the number are significant.

Which of the following is the most appropriate method for safely handling an acid spill in a laboratory?

D.Soaking up the acid with an acid-neutralizing absorbent pad Option (D) is correct. The pH of the acid should be neutralized before handling, but never by increasing the volume of the spill with a strong base. Laboratory safety kits typically include absorbent pads or baking soda to help neutralize and absorb acid spills.

In which of the following cell types is a mutation most likely to have an impact on the gene pool of a population?

D.Sperm Option (D) is correct. Mutations in DNA may result in changes in protein structure and expression. These changes may affect the fitness of an individual in its environment. If the changes occur in gametes, then the changes can be inherited and influence the population's gene pool.

Which of the following is an example of asexual reproduction in plants?

D.Strawberry plants produced by runners from other strawberry plants Option (D) is correct. Strawberry plants produce horizontal shoots called runners or stolons that grow along the surface of the soil. Plantlets that are genetically identical to the parent plant form and take root at nodes along each runner.

Which of the following best characterizes a cross between a homozygous recessive individual and an individual with the dominant phenotype, but whose genotype is unknown?

D.Testcross Option (D) is correct. This characterizes a classic testcross used to determine if an individual with a dominant phenotype is genotypically homozygous dominant or heterozygous. If progeny of the cross all express the dominant phenotype, the parent with the dominant phenotype is almost certainly homozygous dominant, but if about 50 percent of the progeny express the recessive phenotype, the parent with the dominant phenotype must be heterozygous.

Bacterial samples were counted every hour from a flask being incubated at 37°C on a shaker. Which of the following was most likely being studied?

D.The growth rate of bacteria Option (D) is correct. Depending on the concentration of particular nutrients in bacterial broth, bacteria exhibit exponential growth (log phase) or are not growing and are in lag phase or stationary phase. The number of bacteria present in samples of equal size can be determined and plotted on a semilog graph (time versus log of numbers of bacteria) to analyze bacterial growth rate.

Which of the following is most likely true about the first cells that arose on Earth?

D.They were anaerobes. Option (D) is correct. The first cells, primitive prokaryotes that were probably heterotrophic, arose on Earth at least 3.5 billion years ago. They were obligate anaerobes because no oxygen was present in the atmosphere. Oxygen only entered the atmosphere when bacteria similar to today's cyanobacteria arose and split water as they carried out photosynthesis.

Sea star wasting syndrome is decimating some populations of sea stars along the North American Pacific coast. Sea stars are the only natural predator of sea urchins and mussels in some portions of this ecosystem. Which of the following is most likely a concern of scientists studying the ecosystem?

D.Without sea stars, the sea urchin and mussel populations will increase and eliminate other species in the ecosystem. Option (D) is correct. Sea stars are keystone species, critical members of the North American Pacific coast ecosystem that includes sea urchins and mussels. If the sea stars die out, the populations of sea urchins and mussels will potentially expand until they eliminate all members of their prey species, at which point they may starve and die out as well. Elimination of the sea urchins and mussels will also allow their prey species to expand, at least for a time, and the balance of the ecosystem will be completely disrupted.

A type of selection that exists between certain inherited conditions and environmental pressures, such as between sickle cell anemia and malaria, that stabilizes the frequency of both alleles is called

D.balanced polymorphism Option (D) is correct. A mutant allele that causes disease in a homozygous state may persist in a population at a frequency higher than expected if individuals who are heterozygous (carriers) have an advantage over individuals with two copies of the wild-type allele. Individuals with sickle cell anemia make a mutant form of hemoglobin that forms long chains and causes distortion of the red blood cells. Carriers make a sufficient amount of the wild-type hemoglobin that they generally experience disease symptoms only when deprived of oxygen. Malaria is caused by the plasmodium parasite, which reproduces in the red blood cells of its host. If Plasmodium infects an individual who is heterozygous for the allele associated with the hemoglobin mutation, the red blood cells rupture much more rapidly than those of an individual homozygous for the wild-type hemoglobin and the parasite has no time to reproduce and make the individual ill. Hence, individuals who are heterozygous for the mutant hemoglobin allele have a survival advantage over individuals homozygous for the wild-type allele in areas where malaria is endemic.

A student is studying a certain species of bacterium. In this species, the student has identified a certain operon that is inducible. The student causes a mutation in the regulatory gene so that the repressor protein is not synthesized. The most likely result of this mutation is that the structural genes in the operon will

D.be continuously transcribed in both the presence and the absence of the inducer Option (D) is correct. In an inducible operon, the repressor protein binds to the operator region of the operon in the absence of the inducer (generally a nutrient, such as lactose) and blocks transcription of the structural genes (the products of which are generally used to metabolize the inducing nutrient). In the presence of the inducer, the inducer binds to the repressor protein and changes its shape such that it disengages from the operator and no longer blocks transcription. If the repressor is absent, the operon may be continuously transcribed, even in the absence of the inducer.

Humans, reptiles, birds, and fish all belong to the same

D.phylum Option (D) is correct. Humans, reptiles, birds, and fish are all members of the phylum Chordata, but they belong to unique classes, orders, and families.

Skin color in humans appears to show a continuous distribution. In an examination of pedigrees, no recognizable pattern of Mendelian inheritance is found with respect to skin color. The data suggest that inheritance of skin color in humans is

D.polygenic Option (D) is correct. Many different genes contribute to skin color, and the combined activity of the genes determines how light or dark is a person's skin.

Which of the following profiles of a country's age structure best represents the most rapid population growth?

The tent picture dark at the bottom Option (A) is correct. As illustrated in the option, as the age of individuals in the population increases, the number of individuals decreases. Hence there are a great many more young than elderly individuals. As the young individuals reach reproductive age and have children, the country will experience rapid population growth.