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New Zealand Scholarship Biology study materials
New Zealand Scholarship Biology study resources

New Zealand Scholarship Biology practice questions

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Question 1Biology (content domains not enumerated in source)

In an enzyme-catalysed reaction, which change explains why a competitive inhibitor raises the substrate concentration needed to reach half of the maximum rate?

  1. The inhibitor increases the affinity of the enzyme for its substrate at low concentrations.
  2. The inhibitor binds the active site, so more substrate is needed to outcompete it for occupancy. Correct answer.
  3. The inhibitor lowers the activation energy of the reverse reaction only.
  4. The inhibitor binds the allosteric site and permanently denatures the enzyme's tertiary structure.

Explanation

A competitive inhibitor resembles the substrate and occupies the active site, so substrate and inhibitor compete for the same binding site. Increasing substrate concentration outcompetes the inhibitor, so the apparent Km rises while Vmax can still be reached.

Question 2Biology (content domains not enumerated in source)

A population of insects is exposed to an insecticide for many generations. Which observation is the best evidence that resistance evolved by natural selection rather than by individual insects acquiring tolerance during their lifetime?

  1. Survivors pass resistance to offspring even when never exposed to the insecticide. Correct answer.
  2. Survivors are larger than insects that died after exposure.
  3. Exposure to the insecticide causes mutations in the insects' detoxification genes.
  4. The insecticide becomes less potent after being stored for a long period.

Explanation

Heritable resistance that appears without further exposure shows the trait is genetically based and was selected for, which is the signature of natural selection. Acquired tolerance during a lifetime would not be inherited in the absence of exposure.

Question 3Biology (content domains not enumerated in source)

Which statement correctly describes the role of the loop of Henle in a mammalian nephron?

  1. It carries urine directly from the kidney to the bladder.
  2. It actively secretes glucose into the filtrate to be reabsorbed later.
  3. It filters blood plasma under pressure into the Bowman's capsule.
  4. It creates a concentration gradient in the medulla that allows water reabsorption from the collecting duct. Correct answer.

Explanation

The countercurrent multiplier of the loop of Henle establishes an osmotic gradient in the medulla. This gradient lets water leave the collecting duct, especially under the influence of ADH.

Question 4Biology (content domains not enumerated in source)

In a cross between two heterozygous individuals for a single gene with complete dominance, what proportion of the offspring is expected to show the recessive phenotype?

  1. Three quarters
  2. All offspring
  3. One quarter Correct answer.
  4. One half

Explanation

A monohybrid cross of two heterozygotes gives a 1:2:1 genotypic ratio, so only the homozygous recessive class expresses the recessive phenotype. That class is one quarter of the offspring.

Question 5Biology (content domains not enumerated in source)

Which feature of the mammalian heart ensures that blood flows in one direction through the chambers?

  1. Blood is pumped only by the movement of the rib cage during breathing.
  2. The sinoatrial node reverses the direction of the impulse each cycle.
  3. Valves open and close in response to pressure differences between chambers. Correct answer.
  4. Cardiac muscle contracts continuously without relaxation.

Explanation

Heart valves are passive structures that open when pressure upstream exceeds pressure downstream and close when the gradient reverses. This pressure-driven action prevents backflow and keeps flow unidirectional.

Question 6Biology (content domains not enumerated in source)

Which molecule is the immediate energy source used directly by the myosin heads during muscle contraction?

  1. Haemoglobin
  2. ATP Correct answer.
  3. Glucose
  4. Collagen

Explanation

Myosin heads hydrolyse ATP to power the power stroke and to detach from actin. ATP is the direct energy currency for contraction, while glucose is a fuel that must first be respired.

Question 7Biology (content domains not enumerated in source)

In an ecosystem, which group of organisms converts atmospheric nitrogen into forms usable by plants?

  1. Primary consumers such as herbivorous insects
  2. Saprotrophic fungi decomposing leaf litter
  3. Nitrogen-fixing bacteria such as Rhizobium in root nodules Correct answer.
  4. Denitrifying bacteria in waterlogged soils

Explanation

Nitrogen fixation is carried out by bacteria such as Rhizobium, which reduce atmospheric nitrogen to ammonia inside root nodules. This makes nitrogen available for plant assimilation.

Question 8Biology (content domains not enumerated in source)

Which process produces genetic variation by exchanging segments between homologous chromosomes during meiosis?

  1. DNA replication
  2. Fertilisation
  3. Cytokinesis
  4. Crossing over Correct answer.

Explanation

Crossing over occurs between non-sister chromatids of homologous chromosomes during prophase I, creating new allele combinations. This recombination is a major source of genetic variation in gametes.

Question 9Biology (content domains not enumerated in source)

A plant is placed in a sealed chamber and illuminated with bright light. If the carbon dioxide concentration in the chamber is measured over time, what pattern is expected while photosynthesis exceeds respiration?

  1. Carbon dioxide concentration remains constant because the two processes cancel exactly.
  2. Carbon dioxide concentration falls only at night when stomata open.
  3. Carbon dioxide concentration falls steadily as it is fixed into organic compounds. Correct answer.
  4. Carbon dioxide concentration rises because respiration releases more than photosynthesis uses.

Explanation

When the rate of photosynthesis exceeds the rate of respiration, net carbon dioxide uptake occurs. The chamber's carbon dioxide concentration therefore declines as the gas is fixed into sugars.

Question 10Biology (content domains not enumerated in source)

Two islands are separated by a wide ocean channel. Over a long period, the populations on each island diverge until they can no longer interbreed successfully. Which term best describes this process?

  1. Allopatric speciation Correct answer.
  2. Sympatric speciation
  3. Convergent evolution
  4. Artificial selection

Explanation

Geographic separation by the ocean channel reduces gene flow between populations, allowing independent divergence and eventual reproductive isolation. This geographic mode of speciation is allopatric.

Question 11Biology (content domains not enumerated in source)

In a population at Hardy-Weinberg equilibrium, the frequency of a recessive allele is 0.3. What is the expected frequency of heterozygous individuals?

  1. 0.09
  2. 0.42 Correct answer.
  3. 0.21
  4. 0.49

Explanation

With q = 0.3, p = 0.7, and the heterozygote frequency is 2pq = 2 x 0.7 x 0.3 = 0.42. This follows directly from the Hardy-Weinberg expansion p squared plus 2pq plus q squared.

Question 12Biology (content domains not enumerated in source)

A mutation changes a single nucleotide in a coding region, but the resulting protein has the same amino acid sequence as before. Which explanation accounts for this?

  1. The mutation changed the reading frame but not the start codon.
  2. The genetic code is degenerate, so several codons specify the same amino acid. Correct answer.
  3. The ribosome proofreads and repairs the mRNA before translation.
  4. The mutation occurred in an intron and was removed during splicing.

Explanation

Because the genetic code is degenerate, a substitution can produce a synonymous codon that still specifies the same amino acid. Such silent mutations leave the protein sequence unchanged.

Question 13Biology (content domains not enumerated in source)

Which best explains why a small population is more vulnerable to loss of genetic diversity than a large population?

  1. Genetic drift has a stronger effect, and rare alleles are more easily lost by chance. Correct answer.
  2. Natural selection cannot operate in small populations.
  3. Gene flow between small populations is always greater.
  4. Mutation rates are higher in small populations than in large populations.

Explanation

In small populations, random sampling of alleles between generations causes stronger genetic drift, so rare alleles are more likely to be lost. This reduces diversity and adaptive potential.

Question 14Biology (content domains not enumerated in source)

In a food web, a keystone predator is removed from a rocky shore community. Which outcome is most consistent with the keystone concept?

  1. All species in the community increase equally in abundance.
  2. Energy transfer to higher trophic levels becomes more efficient.
  3. A dominant prey species expands and outcompetes other species, reducing diversity. Correct answer.
  4. The community becomes more diverse because competition is reduced.

Explanation

A keystone predator exerts disproportionate control by suppressing a dominant competitor. Its removal lets that prey species expand and exclude others, often lowering community diversity.

Question 15Biology (content domains not enumerated in source)

Which structural feature of an insect's gas exchange system allows efficient oxygen delivery to tissues without a circulatory transport step?

  1. Lungs with alveoli provide a large surface area for diffusion.
  2. Gills with countercurrent flow maximise oxygen uptake from water.
  3. Haemoglobin in closed blood vessels carries oxygen to tissues.
  4. A network of tracheae and tracheoles delivers air directly to cells. Correct answer.

Explanation

Insects use a tracheal system in which air-filled tubes branch into tracheoles that reach individual cells. Oxygen diffuses directly to tissues, so a blood-based transport step is not required.

Question 16Biology (content domains not enumerated in source)

A student measures the rate of an enzyme reaction at several temperatures. The rate rises, peaks, then falls sharply. Which explanation best accounts for the fall after the peak?

  1. Thermal energy disrupts hydrogen bonds and other interactions, denaturing the enzyme's active site. Correct answer.
  2. Substrate molecules gain kinetic energy and collide less frequently at high temperature.
  3. Enzyme molecules are consumed stoichiometrically as the reaction proceeds.
  4. The enzyme's activation energy increases as temperature rises.

Explanation

Beyond the optimum, increased thermal energy breaks the weak bonds maintaining tertiary structure, so the active site loses its shape. Denaturation reduces the reaction rate sharply.

Question 17Biology (content domains not enumerated in source)

In a dihybrid cross between two individuals heterozygous for both genes, assuming independent assortment, what proportion of offspring is expected to show both recessive traits?

  1. 1/16 Correct answer.
  2. 3/16
  3. 9/16
  4. 1/4

Explanation

Each gene independently gives a one-quarter chance of the recessive phenotype, so the combined probability is one-quarter times one-quarter, which equals 1/16. This is the double recessive class of the 9:3:3:1 ratio.

Question 18Biology (content domains not enumerated in source)

Which feature of the mammalian small intestine is most directly responsible for increasing the surface area for absorption?

  1. Villi and microvilli on the epithelial lining Correct answer.
  2. Rings of smooth muscle in the wall
  3. The presence of gastric glands
  4. The low pH maintained by hydrochloric acid

Explanation

Projections called villi, together with microvilli on the epithelial cells, greatly increase the apical surface area available for absorption. This structural amplification shortens the diffusion path and speeds nutrient uptake.

Question 19Biology (content domains not enumerated in source)

A cell is placed in a hypertonic solution. Which change is expected in a plant cell with a rigid cell wall?

  1. The cell swells until it bursts because of wall pressure.
  2. The protoplast shrinks away from the cell wall as water leaves. Correct answer.
  3. There is no net movement of water because the wall blocks osmosis.
  4. Water enters and turgor pressure increases.

Explanation

In a hypertonic solution, water leaves the cell by osmosis, so the protoplast shrinks and pulls away from the rigid wall, a condition called plasmolysis. The wall prevents the whole cell from collapsing.

Question 20Biology (content domains not enumerated in source)

In a pedigree, a trait appears in every generation and affects about half the offspring of an affected parent, with both males and females affected. Which mode of inheritance is most consistent with this pattern?

  1. Autosomal dominant Correct answer.
  2. Mitochondrial inheritance
  3. X-linked recessive
  4. Autosomal recessive

Explanation

Appearance in every generation with roughly half of an affected parent's offspring affected, and both sexes involved, fits autosomal dominant inheritance. Each affected heterozygote passes the allele to about half its children.

Question 21Biology (content domains not enumerated in source)

A lake receives runoff rich in nitrate and phosphate. Which sequence best describes the likely chain of events?

  1. Algal bloom, then decomposition of dead algae, then oxygen depletion and fish kills Correct answer.
  2. Increased oxygen, then algal death, then reduced decomposition
  3. Oxygen depletion, then algal bloom, then increased fish growth
  4. Nitrate precipitation, then increased water clarity, then plant die-off

Explanation

Nutrient enrichment causes rapid algal growth, and when the algae die, decomposers consume oxygen as they break down the organic matter. The resulting hypoxia can kill fish and other aerobic organisms.

Question 22Biology (content domains not enumerated in source)

In the light-dependent reactions of photosynthesis, what is the immediate consequence of the splitting of water at photosystem II?

  1. NADPH is oxidised back to NADP+ for the Calvin cycle.
  2. Electrons are supplied to replace those lost by the reaction centre, and oxygen is released. Correct answer.
  3. Carbon dioxide is fixed into glucose by rubisco.
  4. ATP synthase is inhibited by the accumulation of protons.

Explanation

Photolysis of water provides electrons to the reaction centre of photosystem II after excitation drives electron loss. The by-product is oxygen, and the electrons flow down the electron transport chain.

Question 23Biology (content domains not enumerated in source)

A gene is transcribed and the primary transcript undergoes alternative splicing. Which outcome is most likely?

  1. The gene is replicated twice, doubling the chromosome number.
  2. Different mature mRNAs, and therefore different protein isoforms, are produced from the same gene. Correct answer.
  3. The polypeptide is synthesised with a completely different reading frame at every codon.
  4. The transcript is exported to the cytoplasm before introns are removed.

Explanation

Alternative splicing joins different combinations of exons, so one gene can yield multiple mature mRNAs and protein isoforms. This expands proteome diversity without requiring additional genes.

Question 24Biology (content domains not enumerated in source)

In a mark-recapture study, 200 animals are caught, marked, and released. Later, 150 animals are caught, of which 30 are marked. Which estimate of population size follows, and what assumption is most critical?

  1. About 1000, assuming the population is closed to births and deaths only
  2. About 450, assuming all animals are recaptured exactly once
  3. About 30, assuming the marked animals remain in the sampled area
  4. About 1000, assuming marked and unmarked animals are equally likely to be recaptured Correct answer.

Explanation

The Lincoln index gives N = (first sample x second sample) / marked recaptures = (200 x 150) / 30 = 1000. The key assumption is that marking does not affect catchability, so marked and unmarked animals mix and are recaptured in proportion to their abundance.

Question 25Biology (content domains not enumerated in source)

Two species of finch with similar beak sizes coexist on an island, but when each occurs alone on separate islands their beak sizes are more similar. Which explanation best fits this observation?

  1. Character displacement reduces competition by selecting for divergence in resource use where the species coexist. Correct answer.
  2. Genetic drift causes convergence in beak size on islands with both species.
  3. The two species interbreed freely, producing intermediate beak sizes.
  4. Gene flow between the species equalises beak size where they coexist.

Explanation

Where the species coexist, competition for shared food resources favours individuals whose beak sizes differ, reducing overlap in resource use. This character displacement produces greater divergence in sympatry than in allopatry.

Question 26Biology (content domains not enumerated in source)

Which statement best describes the role of rubisco in the Calvin cycle of a C3 plant?

  1. It catalyses the fixation of CO2 onto ribulose bisphosphate to form two molecules of 3-phosphoglycerate. Correct answer.
  2. It transfers electrons from NADPH to glycerate-3-phosphate during the reduction phase.
  3. It splits water to release oxygen and electrons for photosystem II.
  4. It phosphorylates ribulose bisphosphate using ATP regenerated in the stroma.

Explanation

Rubisco (ribulose-1,5-bisphosphate carboxylase/oxygenase) catalyses carbon fixation, joining CO2 to the five-carbon RuBP to yield two molecules of the three-carbon 3-PGA. Reduction and regeneration are carried out by other enzymes using ATP and NADPH. Water splitting occurs at photosystem II in the thylakoid membrane, not in the stroma.

Question 27Biology (content domains not enumerated in source)

A student examines a section of tissue and observes cells with densely packed cristae-rich organelles, abundant smooth endoplasmic reticulum, and numerous vesicles. Which cell type is this observation most consistent with?

  1. A mature red blood cell specialised for oxygen transport
  2. A keratinised skin cell at the body surface
  3. A mature sieve tube element in phloem
  4. A steroid-secreting cell such as a Leydig cell Correct answer.

Explanation

Smooth endoplasmic reticulum is the site of steroid synthesis, and steroid secretion requires considerable ATP, consistent with abundant mitochondria with well-developed cristae. Vesicles indicate an active secretory pathway. The other cell types listed are either enucleate, largely inactive metabolically, or lack the machinery for steroid synthesis.

Question 28Biology (content domains not enumerated in source)

In a cross between a heterozygous black guinea pig (Bb) and a white guinea pig (bb), what is the expected ratio of black to white offspring?

  1. 3:1
  2. All black
  3. 1:3
  4. 1:1 Correct answer.

Explanation

A Bb parent produces B and b gametes in equal proportion, while a bb parent produces only b gametes. Half the offspring are Bb (black) and half are bb (white), giving a 1:1 ratio. A 3:1 ratio arises from a cross between two heterozygotes, not from this test cross.

Question 29Biology (content domains not enumerated in source)

Which feature of the xylem vessel elements most directly facilitates the bulk flow of water under tension?

  1. Living protoplasts that actively pump water upward
  2. Perforation plates between stacked elements that reduce resistance to flow Correct answer.
  3. Sieve plates that connect adjacent vessel elements
  4. Lignified side walls that prevent any lateral water movement

Explanation

Vessel elements are joined end-to-end, and the end walls break down to form perforation plates, producing a continuous low-resistance tube. This structural adaptation supports bulk flow driven by transpiration pull. The other options misdescribe xylem anatomy or confuse xylem with phloem structure.

Question 30Biology (content domains not enumerated in source)

A patient's blood glucose concentration falls below normal, and glucagon is released. Which response is most consistent with glucagon action?

  1. Increased insulin secretion from pancreatic beta cells
  2. Increased conversion of glucose to glycogen in the liver
  3. Increased uptake of glucose by skeletal muscle via GLUT4 translocation
  4. Increased breakdown of liver glycogen and release of glucose into the blood Correct answer.

Explanation

Glucagon acts primarily on hepatocytes, stimulating glycogenolysis and gluconeogenesis to raise blood glucose. It does not promote glucose uptake into muscle, which is an insulin effect. Glycogen synthesis and further insulin release would lower glucose and are the opposite of the required response.

Question 31Biology (content domains not enumerated in source)

During the cardiac cycle, which event coincides with the first heart sound?

  1. Closure of the semilunar valves at the end of ventricular systole
  2. Closure of the atrioventricular valves at the start of ventricular systole Correct answer.
  3. Opening of the semilunar valves at the start of ventricular ejection
  4. Passive filling of the ventricles during diastole

Explanation

The first heart sound is produced by the closure of the atrioventricular (mitral and tricuspid) valves as ventricular pressure rises above atrial pressure at the start of systole. The second heart sound corresponds to semilunar valve closure. Valve opening and passive filling are silent events.

Question 32Biology (content domains not enumerated in source)

Which statement best explains why the resting membrane potential of a typical neuron is close to the equilibrium potential for potassium?

  1. The membrane is highly permeable to K+ at rest, so the potential is dominated by the K+ gradient. Correct answer.
  2. Chloride ions are actively transported out of the cell to maintain the negative interior.
  3. Voltage-gated sodium channels remain open at rest, allowing Na+ to set the potential.
  4. The sodium-potassium pump moves equal numbers of Na+ and K+ ions across the membrane.

Explanation

At rest, leak channels make the membrane far more permeable to K+ than to other ions, so the membrane potential approaches the K+ equilibrium potential determined by the concentration gradient. The pump contributes a small electrogenic effect but does not move equal numbers of ions. Voltage-gated Na+ channels are closed at rest.

Question 33Biology (content domains not enumerated in source)

In a species of flowering plant, flowers may be red or white, and this trait is controlled by a single gene with incomplete dominance. What phenotypic ratio is expected from a cross between two pink-flowered plants?

  1. 1 red : 2 pink : 1 white Correct answer.
  2. All pink
  3. 1 red : 1 white
  4. 3 red : 1 white

Explanation

With incomplete dominance, heterozygotes show an intermediate phenotype (pink). Crossing two heterozygotes gives a 1:2:1 genotypic ratio, which is also the phenotypic ratio because each genotype has a distinct phenotype. A 3:1 ratio would occur only with complete dominance.

Question 34Biology (content domains not enumerated in source)

Which best describes the role of the sodium-potassium pump in maintaining the resting potential of a neuron?

  1. It directly produces the neurotransmitter released at the synapse.
  2. It maintains the concentration gradients of Na+ and K+ that underlie the resting potential. Correct answer.
  3. It generates the action potential by opening voltage-gated channels.
  4. It transports glucose into the neuron for ATP production.

Explanation

The pump uses ATP to move three Na+ out and two K+ in, maintaining the gradients that drive the resting potential and allow action potentials to occur. It does not itself generate action potentials or release neurotransmitters. Glucose transport is carried out by separate transporters.

Question 35Biology (content domains not enumerated in source)

A researcher finds that a particular enzyme has a high Km for its substrate. What does this indicate about the enzyme?

  1. It has a high affinity for the substrate and reaches half-maximal velocity at low substrate concentration.
  2. It has a low affinity for the substrate and requires a higher substrate concentration to reach half-maximal velocity. Correct answer.
  3. It has a higher Vmax than an enzyme with a low Km.
  4. It is inhibited competitively by its own substrate.

Explanation

Km is the substrate concentration at which the reaction proceeds at half of Vmax, so a high Km reflects weaker substrate binding (lower affinity). Vmax is independent of Km, and Km does not indicate substrate inhibition. The relationship between Km and affinity is inverse.

Question 36Biology (content domains not enumerated in source)

Which process directly produces the ATP synthesised during oxidative phosphorylation in mitochondria?

  1. Substrate-level phosphorylation in the citric acid cycle
  2. Decarboxylation of pyruvate to acetyl-CoA
  3. Reduction of oxygen to water at complex IV
  4. Chemiosmotic coupling through ATP synthase driven by a proton gradient Correct answer.

Explanation

Electron transport pumps protons into the intermembrane space, creating a gradient that drives ATP synthase to phosphorylate ADP. This chemiosmotic mechanism accounts for most ATP produced in aerobic respiration. The other options describe steps that generate reduced coenzymes or a small amount of ATP by substrate-level phosphorylation, not the main oxidative phosphorylation output.

Question 37Biology (content domains not enumerated in source)

In a mesocosm experiment, a small population of a self-pollinating plant species is maintained at low numbers for many generations. Which outcome is most likely?

  1. Rapid adaptation to environmental change
  2. Increased heterozygosity due to recombination
  3. Reduced genetic variation due to genetic drift and inbreeding Correct answer.
  4. Increased mutation rate due to small population size

Explanation

Small populations experience strong genetic drift, and self-pollination promotes inbreeding, both of which reduce heterozygosity and overall genetic variation. Reduced variation limits adaptive potential rather than enhancing it. Mutation rate is not directly increased by small population size.

Question 38Biology (content domains not enumerated in source)

Which observation provides the strongest evidence that a trait is subject to stabilising selection?

  1. The mean value of the trait shifts in one direction over successive generations.
  2. Two distinct phenotypic peaks persist in the population.
  3. Both extremes of the trait are selected against, and the intermediate phenotype is favoured. Correct answer.
  4. The trait becomes more variable over time with no change in mean.

Explanation

Stabilising selection favours intermediate phenotypes and reduces variation by selecting against both extremes, so the mean stays similar while variance decreases. Directional selection shifts the mean, and disruptive selection produces two peaks. Increasing variance without a mean shift is not stabilising selection.

Question 39Biology (content domains not enumerated in source)

A population of insects develops resistance to a pesticide within a few years. Which explanation best accounts for this rapid change?

  1. The pesticide increases the mutation rate in exposed insects.
  2. Pre-existing resistant alleles increase in frequency because susceptible individuals are killed. Correct answer.
  3. Individual insects learn to detoxify the pesticide and pass this ability to offspring.
  4. The pesticide induces targeted mutations that confer resistance.

Explanation

Resistance evolves because genetic variation for resistance already exists in the population, and pesticide application removes susceptible individuals, raising the frequency of resistant alleles. Mutations are not induced in a targeted way by the pesticide, and acquired traits are not inherited. Rapid change reflects strong selection on standing variation.

Question 40Biology (content domains not enumerated in source)

Which statement best describes the relationship between a species' fundamental niche and its realised niche?

  1. The fundamental niche excludes abiotic factors and includes only competitors.
  2. The realised niche is always larger than the fundamental niche.
  3. The realised niche is the portion of the fundamental niche actually occupied in the presence of biotic interactions. Correct answer.
  4. The two niches are identical for all species in a community.

Explanation

The fundamental niche describes the full range of conditions a species could occupy without competitors or predators, while the realised niche is the narrower portion actually occupied because of biotic interactions. Competition and predation typically restrict the realised niche. The two are not necessarily identical.

Question 41Biology (content domains not enumerated in source)

A researcher measures the rate of oxygen uptake by a small mammal at different ambient temperatures. Uptake stays constant across a range of temperatures and then rises sharply as temperature falls further. Which interpretation is most appropriate?

  1. The mammal's metabolic rate is independent of temperature at all points.
  2. The mammal is ectothermic and its metabolic rate follows ambient temperature passively.
  3. The mammal is entering torpor at the lower temperatures.
  4. The mammal is endothermic and increases metabolic heat production to maintain body temperature. Correct answer.

Explanation

A constant metabolic rate over a range of temperatures indicates thermoregulation, and the increase at low temperatures reflects elevated heat production to offset heat loss. This is characteristic of endotherms. An ectotherm's rate would fall with temperature, and torpor would reduce rather than increase metabolism.

Question 42Biology (content domains not enumerated in source)

Which feature of the mammalian kidney is most directly responsible for creating the osmotic gradient used to concentrate urine?

  1. The secretion of hydrogen ions into the distal tubule
  2. The reabsorption of glucose in the proximal convoluted tubule
  3. The filtration of plasma in the glomerulus under high hydrostatic pressure
  4. The countercurrent arrangement of the loop of Henle with descending and ascending limbs of differing permeability Correct answer.

Explanation

The loop of Henle uses a countercurrent multiplier: the descending limb is permeable to water but not salt, while the ascending limb is permeable to salt but not water. This arrangement builds an osmotic gradient in the medulla that allows water reabsorption from the collecting duct. Filtration, glucose reabsorption, and ion secretion do not establish this gradient.

Question 43Biology (content domains not enumerated in source)

A gene is expressed only in a specific tissue because a transcription factor binds an enhancer sequence in that tissue. Which statement best explains how this enhancer acts?

  1. It prevents translation of the mRNA in other tissues.
  2. It directly codes for the transcription factor that activates the gene.
  3. It increases transcription by interacting with the promoter through DNA looping and recruiting RNA polymerase. Correct answer.
  4. It removes introns from the primary transcript.

Explanation

Enhancers are regulatory DNA sequences that bind transcription factors and, through looping, contact the promoter to increase transcription initiation. They do not encode proteins, block translation, or catalyse splicing. Their action is at the level of transcription.

Question 44Biology (content domains not enumerated in source)

Which statement best distinguishes the roles of mitosis and meiosis?

  1. Mitosis produces haploid cells for sexual reproduction, while meiosis produces diploid cells for growth.
  2. Mitosis halves the chromosome number, while meiosis maintains it.
  3. Mitosis produces genetically identical diploid cells for growth, while meiosis produces haploid gametes with genetic variation. Correct answer.
  4. Both processes produce gametes, but meiosis occurs only in plants.

Explanation

Mitosis produces daughter cells genetically identical to the parent, supporting growth and repair, while meiosis halves the chromosome number and generates variation through crossing over and independent assortment. The other options reverse or misstate these roles.

Question 45Biology (content domains not enumerated in source)

In a population, a new allele arises by mutation and is initially present in a single individual. Which factor most strongly determines whether this allele will become common?

  1. Whether the allele confers a fitness advantage in the current environment Correct answer.
  2. The number of chromosomes in the species
  3. Whether the allele is located on an autosome or a sex chromosome
  4. Whether the allele is dominant or recessive

Explanation

Natural selection acts on phenotypes, so an allele that improves survival or reproduction will tend to increase in frequency, while a deleterious allele will be removed. Dominance affects expression but not the direction of selection in the same way. Chromosome number and chromosome type do not determine the allele's fate.

Question 46Biology (content domains not enumerated in source)

Which structural feature of the mammalian alveolus most directly facilitates efficient gas exchange?

  1. A large surface area with a thin, moist epithelium in close contact with capillaries Correct answer.
  2. Cilia that move oxygen across the alveolar surface
  3. Cartilage rings that keep the alveolus open
  4. A thick, muscular wall that pumps air into the bloodstream

Explanation

Alveoli provide an enormous surface area with walls only one cell thick, separated from the capillary endothelium by a thin interstitial space, which shortens the diffusion distance. They are also moist, allowing gases to dissolve. Thick muscular walls, cartilage, and cilia do not serve gas exchange.

Question 47Biology (content domains not enumerated in source)

Two populations of a lizard species are separated by a mountain range. After many generations, they can no longer interbreed successfully. Which term best describes this outcome?

  1. Convergent evolution
  2. Allopatric speciation Correct answer.
  3. Sympatric speciation
  4. Adaptive radiation

Explanation

Speciation following geographic separation of populations is allopatric speciation, in which reduced gene flow allows divergence and reproductive isolation. Sympatric speciation occurs without geographic separation, and the other terms describe different evolutionary patterns.

Question 48Biology (content domains not enumerated in source)

A marine ecosystem receives a large input of nutrients from agricultural runoff. Which sequence best describes the likely consequences?

  1. Increased algal growth, followed by decomposition that depletes oxygen and harms animal life Correct answer.
  2. Decreased algal growth, followed by increased oxygen levels and greater biodiversity
  3. Reduced nutrient availability, followed by increased primary productivity
  4. Immediate increase in dissolved oxygen, followed by decline in fish populations

Explanation

Nutrient enrichment promotes algal blooms; when the algae die, bacterial decomposition consumes oxygen, creating hypoxic conditions harmful to animals. This is eutrophication. The other options reverse the causal sequence or the oxygen dynamics.

Question 49Biology (content domains not enumerated in source)

In a population of 500 individuals, 180 are homozygous dominant, 240 are heterozygous, and 80 are homozygous recessive for a single locus. What is the frequency of the recessive allele?

  1. 0.80
  2. 0.40 Correct answer.
  3. 0.32
  4. 0.16

Explanation

The recessive allele frequency q equals the frequency of homozygous recessive individuals plus half the frequency of heterozygotes: 80/500 + 240/(2 x 500) = 0.16 + 0.24 = 0.40. This follows directly from allele counting. The value 0.16 is the frequency of homozygous recessive genotypes, not the allele frequency.

Question 50Biology (content domains not enumerated in source)

A drug binds to the active site of an enzyme and competes with the substrate. Which change in kinetic parameters is expected as inhibitor concentration increases?

  1. Both Vmax and Km decrease
  2. Vmax decreases and Km remains unchanged
  3. Vmax remains unchanged and Km increases Correct answer.
  4. Both Vmax and Km increase

Explanation

Competitive inhibition can be overcome by raising substrate concentration, so Vmax is unchanged, but more substrate is needed to reach half-maximal velocity, so the apparent Km increases. Non-competitive inhibition instead lowers Vmax. The other options describe patterns inconsistent with competitive inhibition.