Biology Praxis 2

A biologist reports the length of a captured snake as 105.030 cm. How many significant figures are in the measurement? A. Three B. Four C. Five D. Six

*D. Six* The measurement 105.030 contains six significant figures. All nonzero numbers are significant, zeros btwn nonzero numbers are significant, & zeros to the right of the decimal point & at the end of the number are significant.

Which of the following is an example of asexual reproduction in plants? A. Self-pollination in pea plants B. Production of many fern sporophytes from a fern gametophyte C. Production of fruit with many seeds, as in tomatoes D. Strawberry plants produced by runners from other strawberry plants

*D. Strawberry plants produced by runners from other strawberry plants* 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 & take root at nodes along each runner.

Which of the following is most likely true about the first cells that arose on Earth? A. They used cilia for locomotion. B. They were eukaryotes. C. They were photosynthetic. D. They were anaerobes.

*D. They were anaerobes.* The 1st 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 & split water as they carried out photosynthesis.

Behavioral biologist Konrad Lorenz noticed that baby geese considered him to be their mother if he was the 1st image they saw immediately upon hatching. The baby geese were exhibiting which of the following behaviors? A. Habituation B. Trial & error C. Territoriality D. Imprinting

*D. Imprinting* 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.

In photosynthesis, light energy is converted to chemical energy w/ an efficiency of approximately A. 100% B. 33% C. 5% D. 1%

*D. 1%* 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.

An individual w/ the genotype AabbccDd mates w/ an individual w/ the genotype AabbCCDd. Which of the following is the expected frequency of offspring with the genotype AaBbCcDd ? A .0 B. 1818 C. 1414 D. 1212

*A. 0* 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' B. 3' A C T C C C G T A 5' C. 5' A U G C C C U C A 3' D. 5' T A C G G G A G T 3'

*A. 3' U A C G G G A G U 5'* A strand of messenger RNA has a base sequence complementary to that of the DNA template strand, & the strand orientations are antiparallel. The only difference btwn DNA-DNA & 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. B. A population is composed of more species than is a community. C. Populations exist independently of communities. D. Communities and populations are equivalent.

*A. A community is composed of populations.* 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 B. A line graph C. A stem-and-leaf plot D. A histogram

*A. A pie chart* Pie charts are circular graphs in which each sector illustrates a proportion of a whole. A pie chart best illustrates & allows comparison of the % of all hospital-acquired infections that are caused by particular organisms.

A diploid organism has the genotype AaBbCc for 3 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 B. AB C. AaB D. ACc

*A. AbC* When gametes form, each gamete will contain 1 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 1st gene locus, a B allele or a b allele of the 2nd gene locus, & a C allele or a c allele of the 3rd gene locus.

Which of the following is required to initiate transcription of a particular gene in eukaryotic cells? A. An RNA polymerase associates w/ transcription factors bound to the gene's regulatory sequences. B. A helicase enzyme makes the gene accessible by separating the 2 strands of the chromosome. C. Splicing factors remove the introns of the gene & join the exons. D. An RNA polymerase recognizes & binds to the initiation codon of the gene.

*A. An RNA polymerase associates w/ transcription factors bound to the gene's regulatory sequences.* In eukaryotic cells, an RNA polymerase cannot bind to a gene & 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, & finally the binding of the RNA polymerase.

Reproduction by binary fission occurs in which of the following? A. Bacteria B. Algae C. Viruses D. Fungi

*A. Bacteria* Bacteria divide by binary fission. A bacterium replicates its single chromosome, the 2 chromosomes become isolated at opposite poles of the cell, the bacterium enlarges, & then growth of new cell wall divides the single bacterium into 2 bacteria.

Which of the following occurs in the stroma of chloroplasts? A. CO2 is fixed into organic molecules. B. Sucrose is converted into starch. C. Light energy is absorbed by chlorophyll. D. Glucose is oxidized to provide energy for the cells of the plant.

*A. CO2 is fixed into organic molecules.* CO2 is fixed into organic molecules during the Calvin cycle of photosynthesis that occurs in the stroma of chloroplasts. The sugar product of the Calvin cycle is glyceraldehyde 3-phosphate, a three-carbon sugar.

Which 2 of the following are the best examples of allopatric speciation? A. DNA sequence similarity suggests that the flightless cormorant found on the Galápagos Islands & the flighted cormorants on the mainland share a common ancestor. B. A hinny is the viable, sterile offspring of a female donkey and a male horse and has characteristics of both parents. C. In some snail species, a single mutation reverses the direction in which the shell coils, so that snails whose shells coil in opposite directions cannot mate. D. The Isthmus of Panama separates 2 very similar populations of fish, the Cortez rainbow wrasse in the eastern Pacific Ocean & the blue-headed wrasse in the western Atlantic Ocean.

*A. DNA sequence similarity suggests that the flightless cormorant found on the Galápagos Islands & the flighted cormorants on the mainland share a common ancestor.* & *D. The Isthmus of Panama separates 2 very similar populations of fish, the Cortez rainbow wrasse in the eastern Pacific Ocean & the blue-headed wrasse in the western Atlantic Ocean.* 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 B. Parasitism C. Overcrowding D. Predation

*A. Drought* Drought is an example of a density-independent factor that affects a population b/C it can, for example, cause the poor growth or death of a population of plants w/o the original density of the plant population affecting the outcome

Which 2 of the following are characteristics of triglycerides? A. Each molecule is composed of fatty acids linked to glycerol. B. Each molecule has a hydrophobic end & a hydrophilic end. C. Triglycerides form bilayers spontaneously in aqueous solutions. D. Triglycerides occur as both solids and liquids at room temperature.

*A. Each molecule is composed of fatty acids linked to glycerol.* & *D. Triglycerides occur as both solids and liquids at room temperature.* A triglyceride is composed of 3 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 & 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 B. Lamarck's theory of evolution C. Darwin's theory of natural selection D. Pasteur's germ theory

*A. Endosymbiotic theory* The endosymbiotic theory suggests that mitochondria were aerobic heterotrophic prokaryotes that were ingested by ancestral eukaryotic cells & formed a symbiotic relationship w/ the eukaryotes. Some of these eukaryotes later ingested photosynthetic prokaryotes, the precursors of plastids such as chloroplasts. This explains the fact that both mitochondria & chloroplasts have a double-membrane boundary while other organelles have only a single-membrane boundary, that they can replicate independently of the cell, & 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 B. Habituation C. Imprinting D. Operant conditioning

*A. Fixed action pattern* Fixed action patterns are a sequence of behaviors that are triggered by an external sensory stimulus & 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 B. Acid precipitation C. A decrease in chemical weathering D. The loss of nonrenewable resources

*A. Global warming* Human activities, particularly the burning of fossil fuels & 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, & to a lesser extent, methane & ozone, absorb infrared radiation emitted by Earth & 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 & 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 B. Variola (smallpox) virus C. Streptococcus pneumoniae D. Mycobacterium tuberculosis

*A. Hepatitis B virus* 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.

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 B. Placing the fruit in complete darkness C. Increasing the temperature to 40°C D. Treating the fruit w/ the plant hormone auxin

*A. Introducing ethylene gas into shipping containers or storage rooms* Ripening in fruits & senescence (aging) are caused by the production & 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 & speeding up the ripening process.

On Earth, which 3 of the following are major reservoirs of carbon? A. Limestone B. Oceans C. Sediments of aquatic ecosystems D.Polar ice caps

*A. Limestone* & *B. Oceans* & *C. Sediments of aquatic ecosystems* Limestone, oceans, & 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 & that some farms are now burning to produce electricity? A. Methane B. Ozone C. Carbon dioxide D. Sulfur dioxide

*A. Methane* 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, & burning the methane & 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. B. Plants are at a higher trophic level than animals. C. Plant matter is easier to digest than meat. D. Biomagnification has killed off most of the large predators.

*A. More energy is available at lower trophic levels.* 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 & use much of the energy they consume in respiration. Energy is also lost as heat generated during their metabolic processes & 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.

Acid precipitation can best be decreased by reducing the amount released to the atmosphere of which of the following? A. Nitrogen oxides B. Mercury C. Carbon monoxide D. Carbon dioxide

*A. Nitrogen oxides* Nitrogen oxides & 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 w/ water, oxygen, & 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 THREE of the following essential elements for plant growth are obtained primarily through the roots? A. Nitrogen B. Magnesium C. Carbon D. Potassium

*A. Nitrogen* & *B. Magnesium* & *D. Potassium* Nitrogen, magnesium, & potassium are 3 essential elements for plant growth are obtained from the growth medium through the roots of a plant.

Which of the following substances can cross a biological membrane by simple diffusion without the assistance of transport proteins or channels? A. Oxygen, O2 B. Glucose C. Sodium ions, Na+ D. Chloride ions, Cl-

*A. Oxygen, O2* Substances that are small & 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 B. Exocytosis of zymogen by cells of the pancreas C. Active transport of Na+ & K+ by the sodium-potassium pump D. Mitotic division of an epithelial cell

*A. Phagocytosis of a bacterium by a macrophage* 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 w/ the membrane.

The changes in turgor pressure that cause the stomata of leaves to open & close result primarily from the reversible uptake & loss of which of the following ions by the guard cells? A. Potassium B. Sodium C. Calcium D. Chloride

*A. Potassium* Stomata open when guard cells actively take up K+ from neighboring epidermal cells. Water osmotically follows the K+ & 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 3 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 C. The binding of random large & small ribosomal subunits to mRNAs D. Exchange of DNA btwn homologous nonsister chromatids

*A. Segregation of homologous chromosome pairs at anaphase I* & *B. Independent assortment of chromatids at anaphase II* & *D. Exchange of DNA btwn homologous nonsister chromatids* 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, & the exchange of DNA btwn homologous nonsister chromatids (crossing‑over) that initiates w/ synapsis of homologous chromosome pairs at prophase I.

Which of the following has provided the strongest evidence for the evolution of organisms? A. The fossil record B. The existence of trophic levels C. Variation among species in the number of chromosomes D. Inheritance of acquired characteristics

*A. The fossil record*- is based mainly on the sequence in which fossils have accumulated in sedimentary rock layers. The association of fossils w/ certain rock strata & the advent of radiometric dating techniques allow scientists to determine the age of the fossils they study. A comparison of the similarities & differences btwn fossils in different layers has provided much evidence for the evolution of organisms & was the major source of evidence before the use of other techniques, such as comparative embryology & 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 btwn cyclins & cyclin-dependent kinases is blocked, which halts cell division. B. Binding between growth factors and growth factor receptors on the surface of the cells is blocked, and the cells lyse. C. The tumor-suppressor proteins bind to the spindle apparatus and interfere with chromosome movement, which blocks cell division. D. The tumor-suppressor proteins trigger the cells to dedifferentiate to stem cells.

*A. The interaction btwn cyclins & cyclin-dependent kinases is blocked, which halts cell division.* Progression of the cell cycle is dependent upon the interaction of 2 types of proteins, cyclins & 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 w/ the CDKs & 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 B. The operon model of gene regulation C. Koch's postulates D. Evolution of species

*A. The one gene-one polypeptide hypothesis* 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. B/c each mutation is in a different gene, it strongly suggests that each gene encodes a different enzyme. Enzymes are proteins composed of 1 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. B. The climate must change during the process. C. The pioneer organisms must be better adapted to the environment than the climax community is. D. The process of evolution must continually produce new species to fill available niches.

*A. The organisms living there at a given time must alter the environment.* 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, & grasses, shrubs, & 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. B. The fire eliminates herbivores in the area so the seedlings can grow faster. C. The carbon dioxide left after the fire is used by the seedlings to enhance growth. D. The top branches of the trees are untouched by the fire and create shade needed for seed germination.

*A. The seedlings will have less competition after the fire.* 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. B. The shoot exhibits positive gravitropism; the root exhibits positive phototropism. C. The shoot & root both exhibit positive gravitropism. D. The shoot & root both exhibit positive phototropism.

*A. The shoot exhibits positive phototropism; the root exhibits positive gravitropism.* 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 & stems to gain access to the sunlight. Roots exhibit positive gravitropism, growing down into the soil to gain access to water & 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 & water. B. Reproduction typically occurs asexually by the formation of stolons. C. They only perform anaerobic cellular respiration. D. They fix nitrogen directly from the atmosphere.

*A. The sporophyte is dependent on the gametophyte for nutrients & water.* In nonvascular plants, the gametophyte is the dominant form of the plant, & the sporophyte remains attached to the parent gametophyte & depends on the gametophyte for nutrients & water. This contrasts w/ vascular plants, where the sporophyte is the dominant form of the plant. In gymnosperms & angiosperms the gametophyte is dependent on the sporophyte for protection & nutrients.

When caribou migrate, the weaker ones often become the prey of wolves & 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 b/c of an increase in the wolves' food availability. B. The wolf population will initially decrease b/c the wolves compete with the caribou for the same food. C. The wolf population will initially decrease b/c the stronger caribou begin to use the wolves as a food source. D. The wolf population will not change significantly; only the caribou population will decrease.

*A. The wolf population will initially increase b/c of an increase in the wolves' food availability.* In this example of interacting organisms in a community, the caribou population will weaken b/c of lack of food, making them easier prey for the wolves. W/ the increase in food, more wolves will survive & hence will produce more offspring. W/ time, if the caribou population does not rebound, the # of wolves will also decrease.

Which @ of the following features distinguish viruses from prokaryotes and eukaryotes? A. Viral genomes are composed of DNA or RNA. B. Viruses are surrounded by a carbohydrate capsule. C. Viral proteins are synthesized only by an infected host cell. D. Viruses scavenge ATP from an infected host cell.

*A. Viral genomes are composed of DNA or RNA.* & *C. Viral proteins are synthesized only by an infected host cell.* Viral genomes are composed of DNA or RNA, in contrast to the genomes of prokaryotes & eukaryotes that are always composed of DNA. Viruses do not contain ribosomes or any materials required for translation & cannot synthesize their own proteins, in contrast to prokaryotes & 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. B. Prions reproduce sexually, but viruses do not. C. Viruses are infections, but prions are not. D. Prions contain membrane-bound organelles, but viruses do not.

*A. Viruses contain nucleic acid, but prions do not* 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 & that triggers the misfolding of other similar proteins w/ 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. B. When there is an excess of intracellular cholesterol, cells do not add cholesterol to their cell membranes. C. When there is an excess of intracellular cholesterol, cells synthesize their own cholesterol instead of taking it up from the blood. D. When there is an excess of intracellular cholesterol, cells secrete cholesterol into the blood and tissue fluids.

*A. When there is an excess of intracellular cholesterol, cells do not transcribe the gene encoding the LDL receptor.* A negative feedback mechanism is 1 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. W/ 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 B. bracts C. tendrils D. stolons

*A. cotyledons* Cotyledon is a part of the plant embryo that typically becomes the first leaf of the seedling. However, cotyledons are not true leaves & are derived differently. Flowering plants have either 1 cotyledon (monocots) or 2 cotyledons (eudicots). Cotyledons are found in gymnosperms as well.

Exergonic and endergonic reactions in cells are interrelated in that A. energy released from exergonic reactions can be used to power endergonic reactions B. an exergonic reaction cannot occur without an equivalent endergonic reaction C. reactants are often the same for both types of reactions D. products are often the same for both types of reactions

*A. energy released from exergonic reactions can be used to power endergonic reactions* 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.

Which 2 of the following processes occur as part of DNA replication? A. Polymerases proceed in a 5' to 3' direction along the template strand. B. 1 new strand is synthesized continuously, & 1 new strand is synthesized as a series of Okazaki fragments. C. A polymerase synthesizes RNA primers. D. As the replication enzymes proceed along a DNA molecule, the 2 strands separate & then reanneal.

*B. 1 new strand is synthesized continuously, & 1 new strand is synthesized as a series of Okazaki fragments.* & *C. A polymerase synthesizes RNA primers.* B/c the 2 strands of a DNA molecule run antiparallel to each other, & b/c a single polymerase simultaneously adds nucleotides to the 3' ends of each of the 2 new strands, 1 new strand of DNA is synthesized in a continuous fashion, & 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 dont 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 & the synthesis of each Okazaki fragment. Another DNA polymerase later replaces the RNA primers w/ dNTPs.

A child is born to a man who has red‑green color blindness & 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 A. 0% B. 25% C. 50% D. 75%

*B. 25%* A carrier of a recessive trait must have 1 wild‑type allele & 1 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 1 X & 1 Y chromosome, there is a 50% chance that the gamete from the man will contain the X chromosome, & the X chromosome will have the allele for red‑green color blindness. 1 of the 2 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 w/ the allele for red‑green color blindness. Therefore, there is a 25% (0.5 × 0.5) chance that the child will be a girl w/ 1 of her 2 X chromosomes bearing the allele for red‑green color blindness.

Wind turbines are used for which of the following activities? A. Maintaining a breeze over crops growing in an arid environment w/o using a lot of farm machinery B. Generating electricity w/o burning fossil fuels C. Pumping natural gas w/o injecting chemicals into groundwater D. Circulating water & nutrients in some seas w/o installing ocean floor pumps

*B. Generating electricity w/o burning fossil fuels* Wind turbines harvest a renewable resource, the wind, to produce electricity w/o the necessity of burning fossil fuels, a nonrenewable resource.

Which of the following statements about the stratospheric ozone layer is accurate? A. The ozone layer helps to absorb infrared radiation, preventing it from reaching Earth's surface. B. Accumulation of chlorofluorocarbons (CFCs) in the atmosphere has led to depletion of the ozone layer. C. Depletion of the ozone layer is most apparent in atmospheric regions above the equator. D. Scientists believe that if the use of ozone-depleting agents is stopped, the damage to the ozone layer will repair itself within 5-10 years.

*B. Accumulation of chlorofluorocarbons (CFCs) in the atmosphere has led to depletion of the ozone layer.* Liberation of chlorine atoms from CFCs has been a major factor in the formation of the ozone hole above Antarctica & the thinning of the ozone layer around the globe. Very little chlorine exists naturally in the atmosphere. Ultraviolet radiation breaks down CFCs & releases chlorine. The chlorine atoms can remain in the atmosphere for decades, catalyzing the destruction of ozone molecules & 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? A. Urban megacities B. Agriculture C. Industrial manufacturing D. Wastewater treatment

*B. Agriculture* 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? A. Matthias Schleiden & Theodor Schwann B. Alfred Hershey & Martha Chase C. James Watson & Francis Crick D. George Beadle & Edward Tatum

*B. Alfred Hershey & Martha Chase* Bacteriophages are viruses that reproduce by infecting bacteria. Hershey & Chase infected bacteria w/ bacteriophages in which either the protein coat or the DNA inside the protein coat was labeled w/ a radioisotope. The only radioisotope they detected inside the bacteria or in progeny phages was that associated w/ DNA. Hence, DNA entered the bacteria & 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? A. Aluminum cans should be recycled b/c aluminum is a scarce element in Earth's crust. B. Aluminum cans should be recycled b/c processing of aluminum ore requires a lot of energy. C. Aluminum cans break down easily to contaminate groundwater surrounding a landfill. D. Aluminum cans are coated with lead-based paints that can leach into groundwater surrounding a landfill.

*B. Aluminum cans should be recycled b/c processing of aluminum ore requires a lot of energy.* Aluminum is refined from bauxite in a process that requires a tremendous amount of energy & also releases a lot of CO2 into the atmosphere. Recycling aluminum cans saves energy, reduces CO2 emissions, & decreases the amount of waste entering landfills.

External fertilization is typically found in which of the following organisms? A. Birds B. Amphibians C. Reptiles D. Mammals

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

Investigators have immunized a rabbit w/ Substance P. They are studying the effect of the immunization on production of anti-Substance P antibodies over a 2-week period following the immunization. Which of the following is the best hypothesis for the experiment? A. Rabbits produce antibodies in response to immunization w/ Substance P. B. Antibody production by the rabbit in response to Substance P will increase over a 2-week period. C. Immunization w/ Substance P will not affect antibody production over a 2-week period. D. Immunization w/ Substance P stimulates the immune system of rabbits.

*B. Antibody production by the rabbit in response to Substance P will increase over a 2-week period.* This statement is the only 1 that is directed toward antibody production over the 2-week period & that is specific enough to suggest an analysis. Antibody levels in blood can be determined several times over the 2-week period after drawing small volumes of blood from the rabbit.

Aphids are small insects that rest on the stems & leaves of plants & 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? A. Aphids prevent normal water transport throughout the plant. B. Aphids deplete the sugars normally available for the plant. C. Damage to the phloem reduces transpiration levels. D. Damage to the phloem prevents photosynthesis.

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

Which of the following cell types are most likely to have motile cilia on the surface? A. Yeast & other fungi B. Epithelial cells lining the mammalian trachea C. Bacteria living in a host animal's intestines D. Spermatozoa

*B. Epithelial cells lining the mammalian trachea* The ciliated epithelial cells that line the trachea are covered w/ a thin layer of mucus. Dust & 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, & no cilia are found on bacteria or fungi.

Which 2 of the following are scientific theories? A. Energy can be neither created nor destroyed but can change in form. B. Evolutionary adaptations arise by natural selection. C. Water covers 71% of Earth's surface. D. The # of species in an isolated island-like habitat is determined by an equilibrium btwn the rates of immigration & extinction.

*B. Evolutionary adaptations arise by natural selection.* & *D. The # of species in an isolated island-like habitat is determined by an equilibrium btwn the rates of immigration & extinction.* A scientific theory is an explanation that is generally broad in scope, is supported by a large body of evidence, & that can serve as the basis for new hypotheses & experimentation. The statements in options (B) & (D) are examples of scientific theories b/c both are broad statements that are based on a great deal of scientific data, & both statements can form the basis of new hypotheses that can be tested.

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? A. 40 B. 120 C. 240 D. 360

*D. 360* 3 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.

A volcano erupts, killing 87 percent of the members of a wildflower population. The original population had approximately equal numbers of pink & 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? A. Gene flow B. Genetic drift C. Geographic isolation D. Polymorphism

*B. Genetic drift* 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 & microevolution occurs. The bottleneck effect is one type of genetic drift.

In individuals w/ 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 & is caused by a particular gene w/ an excessive number of repeats of the trinucleotide sequence CAG. The disorder is most likely which of the following? A. Turner syndrome B. Huntington's disease C. Down syndrome D. Rheumatoid arthritis

*B. Huntington's disease* 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 & the age of onset correlate w/ the # of CAG repeats. If a parent passes an allele of the HTT gene w/ a large # 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 w/ an excessive # of repeats is toxic to cells, particularly to brain neurons. Death of the neurons leads to movement, cognitive, & 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 & highly flammable. In which of the following locations should the ether be added to the etherizer? A. At a lab bench in the middle of the lab, b/c the ether smell will rapidly disperse in the large volume of air B. In a fume hood, where the ether fumes are drawn to the outside of the building through an exhaust system C. Outside the building, where fresh air & wind will remove the ether fumes D. At a chemical safety cabinet w/ the door ajar, where the ether bottle is opened w/ 1 hand & the etherizer is held in the other hand

*B. In a fume hood, where the ether fumes are drawn to the outside of the building through an exhaust system* Fume hoods are typically designed so that air is drawn in from the front of the hood & exhausted to the outside or filtered before recirculation back into the hood. W/ 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? A. It is the site of O2 and CO2 exchange. B. It is the source of new blood cells. C. It is the site of tendon attachment. D. It is the source of hormones that control bone growth.

*B. It is the source of new blood cells.* 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 & monocytes, & cells that are precursors to platelets.

Which of the following best describes punctuated equilibrium? A. The forward & reverse directions of a reaction are in equilibrium unless there is an external input of reactants or products. B. Long periods of evolutionary stability are followed by periods of rapid speciation. C. Water accumulates in the contractile vacuole of certain organisms that live in a hypoosmotic environment, but the organisms remove the excess water by periodically contracting the vacuole. D. All organisms in an ecosystem are in equilibrium unless a change occurs to a particular biotic or abiotic factor.

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

The ecological role that an organism plays in the community is known as which of the following? A. Biome B. Niche C. Ecotone D. Territory

*B. Niche* The sum of an organism's use of both abiotic & biotic factors in its community is referred to as the organism's ecological niche.

Which of the following will best help maintain the diversity & abundance of organisms in a terrestrial ecosystem? A. Introducing a new exotic species B. Preventing habitat destruction C. Eliminating predatory species D. Removing weeds & other undesirable plants

*B. Preventing habitat destruction* The single greatest threat to loss of both terrestrial and aquatic biodiversity is habitat destruction by humans. Associated w/ habitat loss is habitat fragmentation, in which organisms are forced to occupy much smaller regions that are more sensitive to environmental changes & 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 w/ defoliant & herbicides for 1 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? A. There will be a decrease in the rate of water runoff & soil erosion from the hillside. B. Secondary succession will occur. C. There will be a decrease in plant biodiversity, but animal biodiversity will remain unchanged. D. The nutrient levels in the soil will remain constant because no plants were using the nutrient resources.

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

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? A. 2% B. 16% C. 32% D. 68%

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

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? A. Both groups are characterized by segmentation during embryonic development. B. The 2 groups have similar patterns of embryonic development. C. In both groups, the early embryo shows spiral cleavage. D. In both groups, three embryonic germ layers develop during gastrula formation.

*B. The 2 groups have similar patterns of embryonic development.* Based on certain aspects of embryonic development, many organisms can be classified by following 1 of 2 developmental modes: protostome development or deuterostome development. Both echinoderms & 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 3 germ layers is found in both deuterostomes and most protostomes, as is segmentation. Typically, protostomes show spiral cleavage & deuterostomes show radial cleavage.

In a particular ecosystem, the number of bobcats has been approximately the same for the past 10 years. Which of the following best explains why the number of bobcats has not changed significantly over the 10-year period? A. Bobcats have a very long reproductive cycle. B. The bobcat population is at carrying capacity. C. The mutation rate within the bobcat population is very low. D. Bobcat immunity to disease has increased over the ten-year period.

*B. The bobcat population is at carrying capacity* 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.

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? A. The folds increase the surface area for the phagocytosis of food particles. B. The folds increase the rate of nutrient absorption by the cells. C. The folds allow the cells to increase the rate of cellular respiration. D. The folds allow expansion of the small intestine after a large meal.

*B. The folds increase the rate of nutrient absorption by the cells.* The smooth intestine is specialized for absorption of nutrients from digested foods. A common motif in cells & 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? A. The material is green. B. The material appears to reproduce on its own. C. The material is composed primarily of carbon & hydrogen atoms. D. The material absorbs heat in the presence of sunlight.

*B. The material appears to reproduce on its own.* 1 of the characteristics of a living thing is that it can reproduce on its own.

Which of the following structures pumps blood out of the mammalian heart? A. Atrium B. Ventricle C. Aorta D. Pericardium

*B. Ventricle* Blood returning to the heart enters the atria, passes through valves into the ventricles, & is pumped out by the ventricles. The right ventricle pumps blood to the lungs, & 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 A. DNA fingerprinting B. bioinformatics C. gene mapping D. genetic engineering

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

The role of denitrifying bacteria in the nitrogen cycle is to A. convert atmospheric nitrogen, N2, to ammonium, NH4+ B. convert nitrate, NO3-, to atmospheric nitrogen, N2 C. assimilate nitrite, NO2-, to amino acids and organic compounds D. release ammonia, NH3, from amino acids and organic compounds

*B. convert nitrate, NO3-, to atmospheric nitrogen, N2* 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 & 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 b/c A. external respiratory organs would invite attack from predators B. gas exchange requires a thin, moist membrane of sufficient surface area to meet the requirements of the animal C. gas exchange requires the use of circulatory pigments D. gas exchange is less efficient on land than in aquatic environments

*B. gas exchange requires a thin, moist membrane of sufficient surface area to meet the requirements of the animal* Infoldings provide a greater surface area for the diffusion of O2 & CO2. The surface must be moist b/c 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 & the alveoli of mammals.

The "beads on a string" analogy used to describe the structure of chromosomes refers to DNA-histone protein complexes called A. ribosomes B. nucleosomes C. nucleoli D. telomeres

*B. nucleosomes* 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.

Chlamydomonas reinhardtii is a unicellular green alga that has a diameter of approximately 10 microns. 10 microns is equivalent to A. 0.01 cm B. 0.001 inch C. 0.01 mm D. 10^-6 m

*C. 0.01 mm* 1 micron ( μmμm) equals 10^-6 m, 10^-4 cm, & 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? A. 18 B. 36 C. 72 D. 144

*C. 72* If a mature ovum contains 18 (n) chromosomes, then the primary oocyte contained 36 (2n) chromosomes. Each chromosome was composed of 2 identical chromatids immediately after DNA replication, which occurred b4 the primary oocyte entered prophase I of meiosis. Hence, 72 chromatids were present in the primary oocyte during prophase I.

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? A. An appearance of genetic mutations in the populations B. An increase in the size of the wildlife preserves C. A decrease in the genetic diversity of the populations D. An increase in the reproductive success of the animals

*C. A decrease in the genetic diversity of the populations* If a population has only a few members and is isolated from other populations, inbreeding will occur, & 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 b/c of the lack of genetic diversity & 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 & current information? A. A lesson taught by the student's teacher B. A science blog on the Internet C. A recent research paper in a scientific journal D. The class textbook

*C. A recent research paper in a scientific journal* Research papers that appear in scientific journals undergo extensive peer review before they are published. A recent research paper will be both current & 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? A. A man who lives to be 70 years old, has no children, & remains very healthy until just before his death B. A man who lives to be 50 years old, has 4 children & 16 grandchildren, & is ill for 5 years before his death C. A woman who lives to be 80 years old, has 6 children & 30 grandchildren, & is in poor health most of her life D. A woman who lives to be 90 years old, has 1 child & no grandchildren, & is ill for 4 years before her death

*C. A woman who lives to be 80 years old, has 6 children & 30 grandchildren, & is in poor health most of her life.* Darwinian fitness is largely defined by the ability to survive, reproduce, & 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. B/c she also has 30 grandchildren, the woman has made a large contribution to the gene pool of 2 generations.

Which of the following physiological responses helps to reduce body temperature? A. Contraction of skeletal muscle B. Release of thyroid hormone C. Activation of the sweat glands D. Release of prostaglandins from the hypothalamus

*C. Activation of the sweat glands* Sweat gland activation releases sweat onto the surface of the skin & allows for evaporative cooling. All the other responses lead to an increase in metabolic heat production & 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? A. Add 472 mL of cold water to 28 mL of the stock sulfuric acid. B. Add 472 mL of hot water to 28 mL of the stock sulfuric acid while vigorously stirring. C. Add 28 mL of the stock sulfuric acid to 400 mL of water, & add water to bring the total volume to 500 mL. D. Add 28 mL of the stock sulfuric acid to 472 mL of water.

*C. Add 28 mL of the stock sulfuric acid to 400 mL of water, & add water to bring the total volume to 500 mL.* 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 M stock sulfuric acid is added to approximately 400 mL of water, & 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 & water are mixed.

What was Antoni van Leeuwenhoek's major contribution to biology? A. Developing a model for the atomic structure of the atom B. Discovering cell walls in cork tissue and coining the term "cell" C. Advancing the field of microscopy through the discovery of bacteria & protists D. Creating the comparative method of organismal biology

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

Which of the following is a recommended safety practice in school biology labs? A. All chemicals should be stored in metal cabinets b/c of the toxic dust & fumes produced by most chemicals. B. Bacteria should not be used because of the danger of human infection by viruses that are carried by bacteria. C. Chemical-resistant gloves & aprons are recommended when performing dissections for protection against preservatives used in the specimens. D. Plastic, rather than glass, beakers & other laboratory ware should be used because of the danger of injury from broken glass.

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

Which of the following best describes the role of buffers in living systems? A. Regulating blood glucose levels B. Controlling levels of growth hormone in the blood C. Combining w/ excess H+ and OH- ions in solution D. Activating anaerobic respiratory pathways

*C. Combining w/ excess H+ and OH- ions in solution* A buffer minimizes changes in the concentration of H+ & OH- ions in a solution. An approximately neutral pH must be maintained in human blood & 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 characterized by the presence of a distinct winter season, fertile soil with litter, & precipitation that is distributed throughout the year? A. Desert B. Grassland C. Temperate forest D. Tropical rain forest

*C. Temperate forest* Temperate forests can be distinguished from other biomes by having distinct seasons, including a winter season; leaf litter contributing to the soil; & rain throughout the year.

Which of the following biomes is correctly paired with the description of its characteristics? A. Taiga: absence of tall plants and trees, low precipitation level, shallow topsoil, and permafrost B. Tundra: presence of cone-bearing trees, high precipitation level, moderate to cool temperatures C. Estuary: salt-marsh grasses, algae, & phytoplankton prevalent, variable water salinity D. Chaparral: presence of grasses, scattered trees, and large herbivores, seasonal rains and droughts, equatorial latitude

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

Which of the following best explains why epidemiologists suggest that a certain percent of the population should be vaccinated against any given contagious pathogen? A. Medical officials know how many people need to be vaccinated so that vaccines in storage are not wasted. B. Drug companies charge the government before making vaccines, & the government needs to recoup the money from patients. C. If a sufficient number of people are vaccinated, unvaccinated people are less likely to encounter an infectious individual & become ill. D. Vaccines are the only way to treat viral diseases, and officials want to vaccinate the people they expect to become infected by certain viruses.

*C. If a sufficient number of people are vaccinated, unvaccinated people are less likely to encounter an infectious individual & become ill.* 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? A. It provides ATP for moving the flagellum. B. It is involved in fusion of the male and female pronuclei. C. It contains enzymes to help the sperm penetrate the egg. D. It is located at the base of the flagellum of the sperm.

*C. It contains enzymes to help the sperm penetrate the egg.* 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 w/ 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? A. Cortex B. Dermis C. Meristem D. Pith

*C. Meristem* Meristem consists of cells that remain undifferentiated & that enable the shoots & roots of the plant to grow in length & girth throughout the life of the plant.

Most cases of Tay‑Sachs disease are caused by which of the following? A. Accumulation of lead in the tissues of a toddler exposed to lead paint B. Ingestion of too much alcohol by an infant's mother during her pregnancy C. Mutations in a gene encoding a particular lysosomal enzyme D. A diet that includes too many foods w/ a high concentration of saturated fats & cholesterol

*C. Mutations in a gene encoding a particular lysosomal enzyme* 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 & spinal cord. As a result, this material accumulates in the lysosomes of the neurons, leading to the destruction of these cells & 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? A. The reduction of NAD+ to NADH and FAD to FADH2 B. The hydrolysis of ATP to ADP + Pi C. Oxidation-reduction reactions as electrons are passed sequentially along members of the electron transport chain D. Substrate-level phosphorylation reactions that occur at several steps of glycolysis & the Krebs cycle

*C. Oxidation-reduction reactions as electrons are passed sequentially along members of the electron transport chain* The electron carriers NAD+ & FAD are reduced to NADH & FADH2, respectively, during glycolysis & the Krebs cycle (citric acid cycle). NADH & FADH2 are then oxidized w/ the simultaneous reduction of early members of the electron transport chain (ETC). A series of redox reactions occurs as the electrons are passed from 1 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 3 members of the electron transport chain to pump protons (H+) against their gradient across the inner membrane of the mitochondrion into the intermembrane space.

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, & 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? A. Animalia B. Fungi C. Protista D. Monera

*C. Protista* 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 & 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 2 pea plants w/ tall stems, some of the offspring had short stems. Which of the following best explains his observation? A. Linkage B. Independent assortment C. Segregation D. Incomplete dominance

*C. Segregation* 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 & recessive alleles determining stem length segregated so that some gametes contained the allele for long stems & 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? A. Nervous system B. Skin C. Stomach lining D. Heart

*C. Stomach lining* The endoderm layer gives rise to the epithelial lining of many organs & body systems, including the liver, pancreas, thyroid gland, urinary bladder, digestive tract, respiratory system, & the reproductive system.

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? A. The DNA will coil tightly around histones. B. The DNA will decompose & be transformed into RNA. C. The DNA will separate into 2 strands as the hydrogen bonds are broken. D. The DNA will become more stable because of an increased number of hydrogen bonds.

*C. The DNA will separate into 2 strands as the hydrogen bonds are broken.* DNA must be heated during each cycle of PCR to break the hydrogen bonds holding the 2 strands together. The temperature of the reaction is then reduced so that added oligonucleotide primers can anneal by the formation of hydrogen bonds w/ the sequences to which they are complementary.

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? A. A large number of endangered species in the park B. The presence of an adequate number of concession stands and restrooms in the park C. The cooperation of individuals who live in the area or have been displaced by the park D. A designated annual hunting season in the park

*C. The cooperation of individuals who live in the area or have been displaced by the park* 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 w/ new homes &/or livelihoods, possibly associated w/ the park, & understand the importance of the park. The individuals will be far more likely to cooperate & 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? A. A species of hummingbird that feeds from a particular flower species cannot efficiently orient its bill to feed from a similar flower species in the same geographic region. B. 1 species of toad breeds in early summer, while a similar species of toad occupying the same geographic range breeds in late summer. C. The hybrid offspring of parents belonging to different equine species do not produce viable gametes. D. Similar species of fish are found in adjacent lakes that formed after an ancient river dried up.

*C. The hybrid offspring of parents belonging to different equine species do not produce viable gametes.* 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 2 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? A. Every water molecule is composed of 2 hydrogen atoms & 1 oxygen atom. B. Water molecules form hydrogen bonds w/ other water molecules. C. The oxygen region of a water molecule has a partial negative charge, & the hydrogen regions have partial positive charges. D. Water molecules are bent, & there is an angle of 109.5° btwn the hydrogen atoms.

*C. The oxygen region of a water molecule has a partial negative charge, & the hydrogen regions have partial positive charges.* B/c of the dipolar nature of water, water forms bonds w/ 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 w/ positively charged ions & the positive hydrogen regions of water molecules bond w/ negatively charged ions. Similarly, water molecules form bonds w/ charged regions of other molecules such as proteins & carbohydrates, & 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? A. The population of the birds in the wintering grounds will increase due to increased food supply. B. The birds will change migration routes to compensate for the loss of wintering grounds. C. The population size of the birds will decrease as fewer birds will return to the breeding grounds. D. The birds will breed in the wintering grounds to save energy.

*C. The population size of the birds will decrease as fewer birds will return to the breeding grounds.* Most migrating songbirds winter in warm locations that generally have good food supplies, & 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, & the birds will be less able to survive the winter & make the long flight back to the breeding grounds. Therefore, fewer birds will return to breed, & there will be a reduction in population size.

Which of the following statements regarding the water cycle is correct? A. On a global scale, there is a net movement of water vapor from the land to the oceans. B. On a global scale, evaporation exceeds precipitation over the land. C. The water cycle differs from other biogeochemical cycles b/c most water moves through ecosystems by physical rather than chemical processes. D. Transpiration by terrestrial plants directly produces surface runoff & groundwater movement from the land to the oceans.

*C. The water cycle differs from other biogeochemical cycles b/c most water moves through ecosystems by physical rather than chemical processes.* 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.

An animal with three distinct body divisions, a pair of antennae, compound eyes, and six legs is most likely A. a tunicate B. a polychaete C. an insect D. a spider

*C. an insect* The features described are all common to insects.

A difference btwn plants & fungi is that plants A. have cell walls B. are multicellular eukaryotes C. are autotrophic D. are decomposers

*C. are autotrophic* 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, & the cells are often multinucleate. The organism is most likely a A. flowering plant B. bacterium C. fungus D. protozoan

*C. fungus* Most fungi are capable of producing hyphae, cells of many types of fungi contain more than one nucleus, & the primary component of fungal cell walls is chitin.

Which of the following is a correct practice when using a light microscope? A. Only the coarse adjustment knob should be used to focus on a specimen when using a high-power objective. B. A drop of oil should be placed on a coverslip b4 viewing a specimen w/ any objective. C. A specimen on a slide should be 1st brought into focus by looking through the ocular lens while bringing the objective lens closer to the slide. D. A specimen on a slide should be located & brought into focus by 1st viewing it with a low-power objective.

*D. A specimen on a slide should be located & brought into focus by 1st viewing it with a low-power objective.* It is far easier to find a specimen under low power b/c a larger portion of the slide is visible. It is also easiest to bring a specimen into focus under low power, & 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? A. The population is increasing in size, and resources are not limiting. B. The population is isolated from other populations of the same species. C. All females produce approximately the same number of progeny each breeding season, and the progeny all survive and successfully reproduce. D. All females of reproductive age prefer to mate with males w/ long, bushy tails.

*D. All females of reproductive age prefer to mate with males w/ long, bushy tails.* 1 of the conditions of Hardy-Weinberg equilibrium is that mating is random. If females preferentially mate w/ certain males, random mixing of gametes will not occur in the population, & genotype frequencies will change.

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? A. Playing sports excessively B. Eating a diet rich in high-fiber foods C. Having a consistently low blood pressure D. Being overweight

*D. Being overweight* 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 & induces the cells to take up glucose from the blood. Evidence exists that in individuals w/ more fatty tissue, body cells have fewer insulin receptors on their membranes, are thus less responsive to insulin, & take up less glucose from the blood.

Which of the following best accounts for the complex regulation of gene expression in multicellular eukaryotic species? A. The presence of a large number of genes B. The presence of promoter regions C. A genome composed of many chromosomes D. Cell- & tissue-specific gene expression

*D. Cell- & tissue-specific gene expression* 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? A. Golgi apparatus B. Nucleus C. Endoplasmic reticulum D. Chloroplast

*D. Chloroplast* Both chloroplasts & mitochondria contain DNA encoding some of their own proteins & also contain their own RNA polymerases & 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? A. Soybeans B. Alfalfa C. Green beans D. Corn

*D. Corn* Nitrogen is the most limiting nutrient in corn production. The root nodules of all legumes, which include soybeans, alfalfa, & green beans, contain nitrogen-fixing bacteria that supply nitrogen to the plants. No such bacteria are associated w/ 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? A. Reserve transcriptase B. Restriction enzymes C. DNA ligase D. DNA primers

*D. DNA primers* 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, & then cooled to allow annealing of the primers to the sample DNA. After the primers anneal, Taq polymerase 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? A. Homologous pairs of chromosomes migrate toward the equator of a dividing cell. B. Each chromosome in a cell is copied and becomes a pair of chromatids. C. Exchange of homologous DNA fragments occurs between sister chromatids. D. DNA-histone interactions cause a gradual increase in chromosome packing.

*D. DNA-histone interactions cause a gradual increase in chromosome packing.* In eukaryotic cells, DNA is associated w/ histones, the complex of which is known as chromatin. Interactions btwn the DNA & the histone proteins lead to the formation of chromosome coils & loops. These coils & 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? A. Estuary B. Open ocean C. Grassland D. Deciduous forest

*D. Deciduous forest* Hurricanes typically have high winds & heavy rainfall. Of the environments listed, the 1 most likely to be affected by both wind & rain is the deciduous forest. The wind & rain contribute to fallen trees & flooding of rivers & streams that will affect many of the organisms inhabiting the forest.

Which of the following organisms is most likely to produce hundreds of eggs, of which only a few will become adult animals? A. Snake B. Whale C. Bird D. Frog

*D. Frog* 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, & 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.

A horticulturist crosses 2 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? A. Multiple alleles B. Simple autosomal dominance C. Sex-linked recessive D. Incomplete dominance

*D. Incomplete dominance* This is a classic example of incomplete dominance in which the cross of 2 plants with an intermediate phenotype produces offspring in which about 50% have the intermediate phenotype & about 25% have each of the 2 phenotypes of the plants initially crossed to produce plants w/ the intermediate phenotype. A plant with only 1 copy of the allele for red pigment produces only enough pigment to be pink; 2 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? A. The cells may be infected with a pathogen that will be transmitted to the recipient. B. Isolation of the cells is labor intensive & expensive. C. Every stem cell line that is developed must receive a patent. D. Isolation of the cells requires destruction of embryos.

*D. Isolation of the cells requires destruction of embryos.* 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 & 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? A. Adaptive radiation B. Genetic drift C. Disruptive selection D. Natural selection

*D. Natural selection* In every population of bacteria treated w/ 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 & will select for those w/ 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 btwn the insect & the plant? A. Commensalism B. Mimicry C. Mutualism D. Parasitism

*D. Parasitism* In a parasitic relationship, one organism benefits while the other is harmed. In the relationship btwn the insect & plant, the insect is protected & gains nutrients from the plant, but the plant is damaged by the insect.

Which of the following is associated w/ pioneer species? A. Understory community B. Climax community C. Late succession D. Primary succession

*D. Primary succession* 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. B/c the soil is nutrient-poor, lichens & mosses or hardy plants w/ extensive root systems are common pioneer species.

Which of the following typically triggers an increase in the respiratory rate of an individual during exercise? A. Glucagon-secreting cells in the pancreas detect a decrease in blood glucose. B. Skeletal muscle cells detect a buildup of lactic acid. C. Sensors in the aorta detect a decrease in blood oxygen. D. Sensors in blood vessels & the medulla detect a decrease in the blood pH.

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

Which of the following is the most appropriate method for safely handling an acid spill in a laboratory? A. Neutralizing the acid w/ a 5 M sodium hydroxide (NaOH) solution B. Diluting the acid w/ water C. Wiping up the acid w/ paper towels D. Soaking up the acid w/ an acid-neutralizing absorbent pad

*D. Soaking up the acid w/ an acid-neutralizing absorbent pad* 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 & 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? A. Liver B. Neuron C. Skin D. Sperm

*D. Sperm* Mutations in DNA may result in changes in protein structure & 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 & influence the population's gene pool.

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? A. Selective cross B. Monohybrid cross C. Dihybrid cross D. Testcross

*D. Testcross* This characterizes a classic testcross used to determine if an individual w/ a dominant phenotype is genotypically homozygous dominant or heterozygous. If progeny of the cross all express the dominant phenotype, the parent w/ the dominant phenotype is almost certainly homozygous dominant, but if about 50% of the progeny express the recessive phenotype, the parent w/ 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? A. The number of conjugating bacteria B. The cell wall structure of bacteria C. The pathogenicity of bacteria D. The growth rate of bacteria

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

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 & mussels in some portions of this ecosystem. Which of the following is most likely a concern of scientists studying the ecosystem? A. The wasting syndrome will spread to all other animals in the ecosystem. B. W/o sea stars, the sea urchins & mussels will start to feed on each other. C. An existing species in the ecosystem will move into the dietary niche of the sea stars. D. W/o sea stars, the sea urchin & mussel populations will increase & eliminate other species in the ecosystem.

*D. W/o sea stars, the sea urchin & mussel populations will increase & eliminate other species in the ecosystem.* Sea stars are keystone species, critical members of the North American Pacific coast ecosystem that includes sea urchins & mussels. If the sea stars die out, the populations of sea urchins & mussels will potentially expand until they eliminate all members of their prey species, at which point they may starve & die out as well. Elimination of the sea urchins & mussels will also allow their prey species to expand, at least for a time, & 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 A. behavioral isolation B. ecological isolation C. hybridization D. balanced polymorphism

*D. balanced polymorphism* 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 w/ 2 copies of the wild-type allele. Individuals w/ sickle cell anemia make a mutant form of hemoglobin that forms long chains & 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 w/ the hemoglobin mutation, the red blood cells rupture much more rapidly than those of an individual homozygous for the wild-type hemoglobin & the parasite has no time to reproduce & 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 A. be transcribed only in the presence of the inducer B. be transcribed only in the absence of the inducer C. not be transcribed in either the presence or the absence of the inducer D. be continuously transcribed in both the presence & the absence of the inducer

*D. be continuously transcribed in both the presence & the absence of the inducer* 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) & 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 & changes its shape such that it disengages from the operator & 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, & fish all belong to the same A. class B. family C. order D. phylum

*D. phylum* Humans, reptiles, birds, & fish are all members of the phylum Chordata, but they belong to unique classes, orders, & families.

Skin color in humans appears to show a continuous distribution. In an examination of pedigrees, no recognizable pattern of Mendelian inheritance is found w/ respect to skin color. The data suggest that inheritance of skin color in humans is A. codominant B. epistatic C. incompletely dominant D. polygenic

*D. polygenic* Many different genes contribute to skin color, & the combined activity of the genes determines how light or dark is a person's skin.

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

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