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NCEA Level 2 Biology study materials
NCEA Level 2 Biology study resources

NCEA Level 2 Biology practice questions

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Question 1Biology achievement standards assessed by internal assessment

A student investigates how light intensity affects the rate of photosynthesis in pondweed. Which change to the experimental design would improve the validity of the investigation?

  1. Using the same pondweed shoot for every trial at each distance
  2. Recording bubbles produced per minute at five different lamp distances Correct answer.
  3. Counting bubbles for the same time period after each distance change
  4. Keeping the lamp distance constant while changing the water temperature

Explanation

Validity means the method actually tests the intended independent variable. Varying lamp distance changes light intensity while other variables such as temperature and carbon dioxide are controlled, so the collected data can be attributed to light intensity. Simply repeating or standardising conditions does not create a valid comparison of intensities.

Question 2Biology achievement standards assessed by internal assessment

In a practical, a student measures the rate of oxygen production by Elodea at increasing light intensities. Which variable is the independent variable in this investigation?

  1. The light intensity Correct answer.
  2. The rate of oxygen production
  3. The temperature of the water
  4. The mass of Elodea used

Explanation

The independent variable is the factor deliberately changed by the investigator to observe its effect. Here light intensity is systematically varied, while oxygen production is the dependent variable measured in response. Temperature and plant mass are controlled variables held constant.

Question 3Biology achievement standards assessed by internal assessment

A student counts bubbles from pondweed three times at each light intensity and calculates an average. Why is calculating an average useful in this investigation?

  1. It removes the need to control temperature during the experiment
  2. It guarantees the data are valid for all pondweed species
  3. It ensures the independent variable has been controlled
  4. It increases the reliability of the results by reducing the effect of random variation Correct answer.

Explanation

Repeated measurements at each setting allow an average to be calculated, which reduces the influence of random fluctuations such as uneven bubbling or counting errors. This improves reliability, meaning the results are more consistent and trustworthy. Averaging does not control variables or guarantee validity across species.

Question 4Biology achievement standards assessed by internal assessment

During a dissection of a mammalian heart, a student identifies the thickest-walled chamber. Which chamber is it, and why is its wall thickest?

  1. Right atrium, because it receives blood from the body
  2. Left ventricle, because it pumps blood around the whole body Correct answer.
  3. Right ventricle, because it pumps blood to the lungs
  4. Left atrium, because it receives oxygenated blood from the lungs

Explanation

The left ventricle has the thickest muscular wall because it must generate enough pressure to pump oxygenated blood through the systemic circulation to the entire body. The right ventricle pumps only to the lungs, a shorter route requiring less pressure, so its wall is thinner. Atria have relatively thin walls because they only move blood into the ventricles.

Question 5Biology achievement standards assessed by internal assessment

A student uses a quadrat to estimate the population of daisies in a school field. Which statement best describes why a quadrat is used rather than counting every daisy?

  1. Quadrat sampling identifies the species present without estimating numbers
  2. Quadrat sampling estimates population size from representative samples Correct answer.
  3. Quadrat sampling gives an exact count of every plant in the field
  4. Quadrat sampling measures the growth rate of individual daisies

Explanation

A quadrat is a sampling tool that allows an estimate of population size based on representative small areas rather than a total count. This is practical when the area is large and counting every individual is impractical. The estimate relies on the samples being randomly placed to be representative.

Question 6Biology achievement standards assessed by internal assessment

In a community, two bird species feed on insects living in the same tree. One species feeds mainly in the upper canopy, the other near the trunk. Which term best describes this pattern?

  1. Resource partitioning Correct answer.
  2. Competitive exclusion
  3. Mutualism
  4. Predation

Explanation

Resource partitioning occurs when species that could compete for the same resource use different parts of it, reducing direct competition. Feeding at different heights within the tree allows both species to coexist. Competitive exclusion would mean one species is eliminated, while mutualism and predation describe different interactions.

Question 7Biology achievement standards assessed by internal assessment

A student investigates enzyme activity by measuring the volume of gas produced when catalase breaks down hydrogen peroxide. Which factor should be kept constant to ensure a fair test of temperature?

  1. The time taken for the reaction to finish
  2. The volume of gas produced
  3. The concentration of the hydrogen peroxide solution Correct answer.
  4. The temperature of the hydrogen peroxide solution

Explanation

When temperature is the independent variable, other factors that affect enzyme activity must be controlled, including substrate concentration. Keeping hydrogen peroxide concentration constant ensures any change in gas production is due to temperature. Gas volume and reaction time are dependent variables, and temperature is deliberately varied.

Question 8Biology achievement standards assessed by internal assessment

In a food web, a small fish eats zooplankton, and a larger fish eats the small fish. If the larger fish population is heavily reduced by fishing, which short-term change is most likely?

  1. The small fish population will stay exactly the same because food webs do not change
  2. The small fish population will decrease because fewer are eaten
  3. The zooplankton population will decrease because more small fish survive Correct answer.
  4. The zooplankton population will increase because fewer small fish survive

Explanation

Removing a predator reduces predation pressure on the small fish, so their population is likely to increase. More small fish then consume more zooplankton, causing the zooplankton population to decline. This illustrates how changes at one trophic level can cascade through a food web.

Question 9Biology achievement standards assessed by internal assessment

A student compares the rate of water uptake by a leafy shoot and a shoot with leaves removed, both placed in similar conditions. Which conclusion is best supported if the leafy shoot takes up more water?

  1. Transpiration from leaves contributes to water movement up the stem Correct answer.
  2. Leaves are the main site of water uptake in plants
  3. Water moves down the stem from leaves to roots
  4. Roots cannot absorb water when leaves are present

Explanation

Water uptake increases when leaves are present because transpiration from leaf surfaces pulls water up the xylem. This supports the idea that transpiration contributes to the upward movement of water. Roots, not leaves, are the site of water uptake, and water moves upward, not downward.

Question 10Biology achievement standards assessed by internal assessment

Which statement correctly describes the role of the xylem in a plant?

  1. It carries out most photosynthesis in the leaf
  2. It controls the opening and closing of stomata
  3. It transports sugars from leaves to other parts of the plant
  4. It transports water and dissolved minerals from roots to leaves Correct answer.

Explanation

The xylem is a transport tissue that moves water and dissolved mineral ions upward from the roots to the shoots and leaves. Sugars are transported in the phloem, while photosynthesis occurs mainly in mesophyll cells and stomatal opening is controlled by guard cells.

Question 11Biology achievement standards assessed by internal assessment

During an ecological study, a student records the number of individuals of each species in a quadrat. Which measure of biodiversity is being directly determined?

  1. Genetic diversity within a species
  2. Species richness Correct answer.
  3. Ecosystem productivity
  4. Trophic level efficiency

Explanation

Species richness is the number of different species present in an area, which is what recording species in a quadrat directly provides. Genetic diversity refers to variation within a species, while productivity and trophic efficiency relate to energy flow rather than species counts.

Question 12Biology achievement standards assessed by internal assessment

A student models a food chain as grass, rabbit, stoat. Approximately what percentage of the energy in the grass is transferred to the stoat?

  1. About 90%
  2. About 10%
  3. About 1% Correct answer.
  4. About 50%

Explanation

Energy transfer between trophic levels is inefficient, typically around 10% per level, because much energy is lost through respiration, heat, and excretion. With two transfers (grass to rabbit, rabbit to stoat), the stoat receives roughly 10% of 10%, which is about 1% of the grass energy.

Question 13Biology achievement standards assessed by internal assessment

A patient's blood test shows a low number of red blood cells. Which function is most directly affected?

  1. Production of antibodies against pathogens
  2. Transport of oxygen around the body Correct answer.
  3. Digestion of food in the stomach
  4. Clotting of blood at a wound

Explanation

Red blood cells contain haemoglobin, which binds oxygen for transport around the body, so a low red blood cell count reduces oxygen-carrying capacity. Clotting involves platelets and plasma proteins, antibodies are produced by white blood cells, and digestion is not a blood cell function.

Question 14Biology achievement standards assessed by internal assessment

Which adaptation of a fish gill increases the rate of gas exchange?

  1. A thick, waterproof covering over the gill filaments
  2. A reduced blood supply to the gill filaments
  3. A low concentration of oxygen in the surrounding water
  4. A large surface area with many thin filaments and lamellae Correct answer.

Explanation

Efficient gas exchange requires a large surface area, thin surfaces for short diffusion distance, and a good blood supply. Many thin filaments and lamellae provide a large, thin surface where oxygen can diffuse into the blood. A thick covering, reduced blood supply, or low oxygen concentration would reduce exchange.

Question 15Biology achievement standards assessed by internal assessment

A student investigates how the surface area to volume ratio of agar cubes affects the rate of diffusion of a dye. Which prediction is best supported by biological principles?

  1. Diffusion will not occur in agar cubes at all
  2. Larger cubes will show a faster rate of diffusion into their centre
  3. Smaller cubes will show a faster rate of diffusion into their centre Correct answer.
  4. Cube size will have no effect on the rate of diffusion

Explanation

Smaller cubes have a larger surface area to volume ratio, so more surface is available relative to the volume that the dye must penetrate. This allows the dye to reach the centre more quickly. This principle helps explain why exchange surfaces in organisms are often thin and folded.

Question 16Biology achievement standards assessed by internal assessment

In an investigation into osmosis, potato cylinders are placed in sucrose solutions of different concentrations. Which result would indicate that a solution is hypotonic to the potato cells?

  1. The potato cylinder shows no change in mass
  2. The potato cylinder loses mass and becomes flaccid
  3. The potato cylinder gains mass and becomes firm Correct answer.
  4. The potato cylinder turns a different colour

Explanation

In a hypotonic solution, water moves into the potato cells by osmosis, increasing the mass and making the tissue firm. A loss of mass would indicate a hypertonic solution, and no change would suggest an isotonic solution. Colour change is not a measure of osmosis in this context.

Question 17Biology achievement standards assessed by internal assessment

A student is asked to explain why a control group is included in an investigation of a fertiliser's effect on plant growth. Which explanation is most accurate?

  1. The control group shows the effect of the fertiliser without any other influences
  2. The control group provides a baseline for comparison so the effect of the fertiliser can be identified Correct answer.
  3. The control group ensures the plants grow at the same rate
  4. The control group increases the number of plants measured

Explanation

A control group is treated identically except that it does not receive the independent variable, here the fertiliser. Comparing the experimental group with the control allows the effect of the fertiliser to be isolated from other factors. It does not itself create growth or increase sample size.

Question 18Biology achievement standards assessed by internal assessment

Two populations of the same insect species live on either side of a wide river and no longer interbreed. Over many generations, they accumulate different genetic changes. Which term describes this process?

  1. Speciation Correct answer.
  2. Artificial selection
  3. Adaptation to a single habitat
  4. Succession

Explanation

Speciation is the formation of new species when populations become reproductively isolated and diverge genetically over time. The river acts as a barrier preventing interbreeding, allowing independent evolution. Succession refers to community change over time, and artificial selection involves human-directed breeding.

Question 19Biology achievement standards assessed by internal assessment

A mutation occurs in a population of bacteria, giving some individuals resistance to an antibiotic. Which statement best explains why the proportion of resistant bacteria increases after antibiotic treatment?

  1. All bacteria become resistant at the same time
  2. The antibiotic is broken down by all bacteria equally
  3. The antibiotic causes bacteria to develop resistance during treatment
  4. Resistant bacteria survive and reproduce, passing the resistance allele to offspring Correct answer.

Explanation

The mutation already exists in some individuals before treatment, and the antibiotic acts as a selection pressure. Resistant bacteria survive and reproduce, so the resistance allele becomes more common in later generations. The antibiotic does not create the mutation, and not all bacteria become resistant simultaneously.

Question 20Biology achievement standards assessed by internal assessment

In a pedigree, a genetic condition appears in every generation and affects both males and females. An affected parent always has at least one affected child, and unaffected parents never have affected children. Which inheritance pattern is most consistent with this evidence?

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

Explanation

Autosomal dominant conditions typically appear in every generation because one copy of the dominant allele causes the condition, and affected individuals usually have an affected parent. Both sexes are affected, consistent with autosomal inheritance. Unaffected parents would not pass on the dominant allele, so they would not have affected children.

Question 21Biology achievement standards assessed by internal assessment

A student crosses two heterozygous pea plants for a single gene with two alleles, where the dominant allele produces purple flowers and the recessive allele produces white flowers. What is the expected ratio of purple to white flowers in the offspring?

  1. 9:3:3:1
  2. 1:1
  3. 3:1 Correct answer.
  4. 1:2:1

Explanation

A monohybrid cross between two heterozygotes (Pp x Pp) gives a genotypic ratio of 1 PP : 2 Pp : 1 pp. Because both PP and Pp show the dominant purple phenotype, the phenotypic ratio is three purple to one white. The 9:3:3:1 ratio arises from a dihybrid cross, not a single gene.

Question 22Biology achievement standards assessed by internal assessment

A student investigates the effect of pH on amylase activity by measuring the time taken for starch to disappear. Which improvement would most increase the reliability of the conclusion?

  1. Repeating each pH trial several times and averaging the times Correct answer.
  2. Changing the temperature between trials
  3. Testing each pH value once to save time
  4. Using a different starch concentration at each pH

Explanation

Reliability is improved by repeating measurements at each pH and averaging them, which reduces the effect of random errors. Single trials may give misleading results. Changing starch concentration or temperature between trials would introduce uncontrolled variables and reduce validity.

Question 23Biology achievement standards assessed by internal assessment

A student is comparing the structure of an insect's tracheal system with that of a mammal's lungs. Which statement correctly describes a difference?

  1. Mammalian lungs deliver air directly to cells without blood, while insect tracheae use blood
  2. Both systems rely on gills for gas exchange
  3. Insect tracheae contain blood, while mammalian lungs do not
  4. Insect tracheae deliver air directly to tissues, while mammalian lungs exchange gases via alveoli and blood Correct answer.

Explanation

In insects, air travels through tracheae and tracheoles that deliver oxygen directly to tissues, while mammals exchange gases in alveoli between air and blood, with blood transporting gases. Tracheae do not contain blood, and neither system uses gills in these organisms.

Question 24Biology achievement standards assessed by internal assessment

A student measures the rate of transpiration in a leafy shoot under different wind speeds and finds that the rate increases as wind speed increases. Which explanation best accounts for this result?

  1. Wind increases the humidity around the leaf, reducing the water potential gradient
  2. Wind removes water vapour from around the leaf, maintaining a steep diffusion gradient Correct answer.
  3. Wind lowers the temperature of the leaf, stopping transpiration completely
  4. Wind closes the stomata, increasing water loss

Explanation

Transpiration depends on a water potential gradient between the moist air inside the leaf and the surrounding air. Wind removes humid air from around the leaf, keeping the gradient steep and allowing more water vapour to diffuse out. This increases the rate of transpiration rather than stopping it.

Question 25Biology achievement standards assessed by internal assessment

In an ecosystem, decomposers such as fungi and bacteria break down dead organic matter. Which statement best describes their role?

  1. They recycle nutrients back into the soil for use by producers Correct answer.
  2. They convert light energy into chemical energy for the ecosystem
  3. They fix nitrogen from the atmosphere into plant proteins
  4. They transfer energy directly to top predators

Explanation

Decomposers break down dead organisms and waste, releasing mineral nutrients into the soil where producers can absorb them. This recycling of nutrients supports continued growth in the ecosystem. They do not capture light energy, feed top predators directly, or fix nitrogen into proteins themselves.

Question 26Biology achievement standards assessed by internal assessment

A student carries out a valid ecological transect across a sand dune and records how the abundance of marram grass changes with distance from the sea. Which statement best describes the purpose of using a transect in this investigation?

  1. To show how the distribution of a species changes along a gradient of an environmental factor Correct answer.
  2. To estimate the total number of species present in the whole dune system
  3. To measure the rate at which individual plants grow over one season
  4. To compare the biomass of producers with that of consumers

Explanation

A transect is a line or belt along which samples are taken so that changes in species distribution can be related to a changing environmental factor such as distance from the sea. It does not by itself estimate total species richness of an area, measure growth rates, or compare trophic levels.

Question 27Biology achievement standards assessed by internal assessment

During a mark-recapture study, 40 snails are caught, marked and released. Later, 50 snails are caught and 8 of them carry a mark. Assuming the population is closed and marks are not lost, which estimate of population size is correct?

  1. 200
  2. 250 Correct answer.
  3. 400
  4. 320

Explanation

The Lincoln index estimates population size as (number marked first × number caught second) ÷ number of marked recaptures. Here that is (40 × 50) ÷ 8 = 2000 ÷ 8 = 250.

Question 28Biology achievement standards assessed by internal assessment

A student uses a key to identify an unknown invertebrate and reaches a couplet asking whether the animal has jointed legs. Which feature of a good biological key does this couplet illustrate?

  1. Each step offers two mutually exclusive alternatives based on observable features Correct answer.
  2. Each step requires the user to know the scientific name before continuing
  3. Each step uses internal anatomy that cannot be seen without dissection
  4. Each step lists several possible species so the user can compare them directly

Explanation

A dichotomous key works by presenting paired, mutually exclusive choices based on features that can be clearly observed. This allows the user to eliminate alternatives step by step without prior knowledge of the answer.

Question 29Biology achievement standards assessed by internal assessment

Two organisms are classified in the same genus but in different species. Which statement about these organisms must be true?

  1. They can always interbreed to produce fertile offspring
  2. They belong to different kingdoms
  3. They occupy identical ecological niches
  4. They share more classification levels with each other than with an organism from a different family Correct answer.

Explanation

Organisms in the same genus share all the higher levels of classification (family, order, class, phylum, kingdom) as well as the genus itself, so they share more levels with each other than with a member of a different family. Being in different species does not guarantee they can interbreed, nor does it fix their kingdom or niche.

Question 30Biology achievement standards assessed by internal assessment

In a practical, a student observes cells from an onion root tip under a microscope to find cells undergoing mitosis. Which feature would identify a cell in anaphase?

  1. Sister chromatids are being pulled to opposite poles of the cell Correct answer.
  2. Chromosomes are lined up along the equator of the cell
  3. Chromatin is condensing into visible chromosomes inside an intact nucleus
  4. The nuclear envelope is reforming around two groups of chromosomes

Explanation

Anaphase is defined by the separation of sister chromatids, which are drawn to opposite poles by the spindle. Alignment at the equator is metaphase, nuclear envelope reformation is telophase, and chromatin condensation marks prophase.

Question 31Biology achievement standards assessed by internal assessment

A student counts cells at each stage of mitosis in a root tip squash and finds 60 cells in interphase, 12 in prophase, 6 in metaphase, 4 in anaphase and 2 in telophase out of 84 cells. Assuming a representative asynchronous sample with similar survival and detectability across stages, which conclusion about time spent in interphase versus mitosis is best supported?

  1. Anaphase is the longest stage of mitosis because chromosomes move furthest
  2. Telophase is the shortest stage because it has the fewest cells
  3. Cells spend most of the cell cycle in interphase, so mitosis occupies a small fraction of the cycle Correct answer.
  4. The root tip contains no dividing cells because interphase cells dominate

Explanation

Under the stated sampling assumptions, the proportion of cells observed in a stage approximates the proportion of time spent there. Interphase contains 60/84 cells, about 71%, while mitosis contains 24/84, about 29%. This supports spending most of the cell cycle in interphase, with a smaller share spent in mitosis.

Question 32Biology achievement standards assessed by internal assessment

During meiosis, crossing over between non-sister chromatids of a homologous pair occurs. What is the main consequence of this event?

  1. Sister chromatids are separated into different gametes
  2. The cell becomes diploid again before gametes form
  3. New combinations of alleles are produced on the chromosomes involved Correct answer.
  4. The chromosome number is halved from diploid to haploid

Explanation

Crossing over exchanges segments between non-sister chromatids, creating recombinant chromosomes with new allele combinations. Halving of chromosome number happens at meiosis I but is a separate outcome of homologous separation, not of crossing over itself.

Question 33Biology achievement standards assessed by internal assessment

A couple who are both carriers of a recessive allele for a genetic disorder have children. What is the probability that a child will show the disorder?

  1. 50%
  2. 25% Correct answer.
  3. 0%
  4. 75%

Explanation

Two carriers are heterozygous (Aa × Aa), giving offspring in the ratio 1 AA : 2 Aa : 1 aa. Only the aa genotype shows the recessive disorder, which is one quarter, or 25%, of the offspring.

Question 34Biology achievement standards assessed by internal assessment

A test cross is set up between an organism showing the dominant phenotype and a homozygous recessive organism. Why is the homozygous recessive partner used?

  1. It ensures all offspring show the dominant phenotype
  2. It prevents crossing over during meiosis
  3. It always produces more offspring than other crosses
  4. It contributes only recessive alleles, so the offspring phenotypes reveal the unknown genotype Correct answer.

Explanation

A homozygous recessive parent passes on only recessive alleles, so any dominant phenotype in the offspring must come from the unknown parent. The ratio of dominant to recessive offspring therefore reveals whether the unknown parent was homozygous dominant or heterozygous.

Question 35Biology achievement standards assessed by internal assessment

In humans, the alleles for blood groups A and B are codominant, and both are dominant to O. A parent with blood group AB and a parent with blood group O have children. Which blood groups are possible in the children?

  1. A and B only Correct answer.
  2. O only
  3. A, B, AB and O
  4. AB and O only

Explanation

The AB parent passes on either the A or the B allele, while the O parent always passes on the O allele. The children are therefore AO (group A) or BO (group B), with no AB or O children possible.

Question 36Biology achievement standards assessed by internal assessment

A mutation changes a single base in a DNA sequence, but the amino acid sequence of the protein produced is unchanged. Which explanation best accounts for this?

  1. The mutation changed the reading frame of the gene
  2. The ribosome corrected the error during translation
  3. The mutation occurred in a non-coding region of the chromosome
  4. The genetic code is degenerate, so more than one codon can specify the same amino acid Correct answer.

Explanation

Because the genetic code is degenerate, several codons code for the same amino acid, so a base substitution can leave the amino acid sequence unchanged. A change of reading frame would usually alter many amino acids rather than leave the protein unchanged.

Question 37Biology achievement standards assessed by internal assessment

Natural selection acts on a population of moths living on dark tree trunks. Which statement best explains why the frequency of dark-coloured moths increases over many generations?

  1. Dark colour is always dominant, so it must increase in frequency
  2. Dark moths are better camouflaged, survive more often and pass on more of their alleles Correct answer.
  3. Individual moths change colour during their lifetime in response to the bark
  4. The moths choose to become darker so they are harder to see

Explanation

Predators remove poorly camouflaged moths, so dark individuals survive and reproduce more successfully, increasing the frequency of their alleles in later generations. Selection acts on existing variation in a population, not on changes acquired by individuals.

Question 38Biology achievement standards assessed by internal assessment

A small population of birds is blown to a remote island and establishes a new colony. Over time, the island population has allele frequencies very different from the original mainland population. Which process best explains this?

  1. Directional selection caused by a new predator
  2. Genetic drift acting on a small founding population Correct answer.
  3. Artificial selection by humans on the island
  4. Gene flow between the island and the mainland

Explanation

When a few individuals found a new population, chance sampling of alleles can produce allele frequencies that differ markedly from the source population, an effect known as the founder effect, a form of genetic drift. Gene flow would tend to make the populations more similar, not more different.

Question 39Biology achievement standards assessed by internal assessment

In a species of lizard, individuals with longer legs run faster on open sand but are easier for predators to spot. Which type of selection is most likely to maintain intermediate leg length in the population?

  1. Stabilising selection Correct answer.
  2. Directional selection
  3. Artificial selection
  4. Disruptive selection

Explanation

Stabilising selection favours intermediate phenotypes when extremes are at a disadvantage, as with long legs being conspicuous and short legs being slow. Directional selection would shift the mean, and disruptive selection would favour both extremes.

Question 40Biology achievement standards assessed by internal assessment

A student investigates the effect of light intensity on the rate of photosynthesis in pondweed by counting oxygen bubbles. Which change would improve the reliability of the results?

  1. Repeat the count at each light intensity and calculate a mean Correct answer.
  2. Change the temperature as well as the light intensity
  3. Count the bubbles for a longer time at only one light intensity
  4. Use a brighter lamp for the whole experiment

Explanation

Reliability is improved by repeating measurements under the same conditions and averaging them, which reduces the effect of random variation. Changing other variables or altering the setup does not improve reliability.

Question 41Biology achievement standards assessed by internal assessment

In a photosynthesis investigation, the rate of oxygen production increases with light intensity up to a point and then levels off. Which explanation best fits this plateau?

  1. Respiration has stopped, so oxygen use no longer offsets production
  2. Another factor such as carbon dioxide concentration or temperature has become limiting Correct answer.
  3. The plant has stopped photosynthesising completely
  4. Light is now being absorbed by the chloroplasts with no effect

Explanation

Once light is no longer limiting, the rate is controlled by the next limiting factor, such as carbon dioxide concentration or temperature. The plateau therefore reflects a different limiting factor, not a complete stop in photosynthesis.

Question 42Biology achievement standards assessed by internal assessment

A student measures the rate of respiration in germinating seeds using a respirometer and finds the rate increases as temperature rises from 20 °C to 35 °C, then falls sharply at 45 °C. Which explanation best accounts for the fall?

  1. The seeds germinate faster at 45 °C and use less oxygen
  2. Respiration becomes anaerobic and produces more carbon dioxide
  3. Enzymes controlling respiration are denatured at high temperature Correct answer.
  4. The seeds have used up all their oxygen at high temperature

Explanation

Respiration is enzyme-controlled, and high temperatures denature the enzymes so the rate falls sharply. The rise before the fall reflects increased kinetic energy and enzyme activity.

Question 43Biology achievement standards assessed by internal assessment

In a mammal, oxygen moves from the alveolus into the blood. Which combination of features of the alveolar wall makes this exchange efficient?

  1. A dry surface with a large volume of air
  2. Thick wall and low blood flow to slow the movement of gases
  3. A moist surface with a small surface area
  4. Thin wall and a rich blood supply maintaining a steep concentration gradient Correct answer.

Explanation

Gas exchange across the alveolus is efficient because the wall is very thin, giving a short diffusion distance, and the dense capillary network removes oxygen and maintains a steep concentration gradient. A large surface area and moist surface also help, but the option combining thin wall with good blood supply is the correct pairing.

Question 44Biology achievement standards assessed by internal assessment

A student compares the oxygen dissociation curves of haemoglobin from a hibernating mammal at low body temperature with the same mammal at normal body temperature. What change is expected at the lower temperature?

  1. The maximum saturation of haemoglobin falls to zero
  2. The curve becomes a straight line, showing no cooperativity
  3. The curve shifts to the left, so haemoglobin releases oxygen less readily Correct answer.
  4. The curve shifts to the right, so haemoglobin releases oxygen more readily

Explanation

Lower temperature reduces the tendency of haemoglobin to release oxygen, shifting the dissociation curve to the left. This means oxygen is held more tightly, which suits a hibernating mammal with a low metabolic rate.

Question 45Biology achievement standards assessed by internal assessment

A student examines a cross-section of a leaf and identifies a layer of cells just below the upper epidermis. Which feature identifies this layer as the palisade mesophyll?

  1. Loosely arranged cells with large air spaces between them
  2. Cells surrounding the stomata that control their opening
  3. Closely packed column-shaped cells rich in chloroplasts near the upper surface Correct answer.
  4. Cells with thickened lignified walls forming a waterproof layer

Explanation

Palisade mesophyll cells are column-shaped, tightly packed and contain many chloroplasts, positioned near the upper surface where light is strongest. Spongy mesophyll is loosely packed, and guard cells surround stomata in the lower epidermis.

Question 46Biology achievement standards assessed by internal assessment

A plant is placed in a sealed transparent chamber and the carbon dioxide concentration is monitored over 24 hours. During the night the carbon dioxide concentration rises, and during the day it falls. Which explanation is correct?

  1. The plant stops respiring when it is illuminated
  2. Photosynthesis occurs only at night and respiration only during the day
  3. Respiration stops during the day so carbon dioxide is only used
  4. Respiration exceeds photosynthesis at night, while photosynthesis exceeds respiration during the day Correct answer.

Explanation

At night there is no light for photosynthesis, so respiration releases carbon dioxide and the concentration rises. In daylight photosynthesis exceeds respiration and net carbon dioxide uptake occurs, so the concentration falls.

Question 47Biology achievement standards assessed by internal assessment

In an investigation into the effect of a fertiliser on plant growth, one group of plants receives distilled water instead of fertiliser solution. Why is this group included?

  1. It shows whether the fertiliser, rather than another variable, caused any difference in growth Correct answer.
  2. It tests whether distilled water contains minerals
  3. It provides extra plants so the sample size is larger
  4. It allows the plants to be grown faster than with fertiliser

Explanation

A control group is treated identically except for the independent variable, so any difference in growth can be attributed to the fertiliser rather than other factors. It is not included to increase sample size or speed growth.

Question 48Biology achievement standards assessed by internal assessment

A student measures the length of 30 leaves from one tree and calculates a mean of 6.4 cm with a standard deviation of 0.8 cm. Another tree gives a mean of 6.5 cm with a standard deviation of 2.5 cm. What does the larger standard deviation tell us about the second tree?

  1. Its leaves are longer on average than those of the first tree
  2. Its mean is less reliable because it was calculated from fewer leaves
  3. Its leaves have a smaller range of lengths
  4. Its leaf lengths are more variable and spread further from the mean Correct answer.

Explanation

Standard deviation measures the spread of values around the mean, so a larger value indicates greater variation in leaf length. It says nothing about the mean itself or the sample size unless those are given.

Question 49Biology achievement standards assessed by internal assessment

In a population of rabbits, a disease kills most individuals with a particular allele, and the survivors breed. Which statement best predicts the effect on the population over several generations?

  1. The susceptible allele becomes dominant so it is expressed more often
  2. The rabbits develop immunity and pass it on to their offspring
  3. The allele frequency stays the same because allele frequencies never change
  4. The frequency of the susceptible allele decreases because fewer individuals carry it to the next generation Correct answer.

Explanation

When individuals carrying an allele die before reproducing, that allele is passed on less often, so its frequency falls in later generations. This is selection acting on the population, not a change acquired by individuals.

Question 50Biology achievement standards assessed by internal assessment

A student is asked to explain why a quadrat is placed randomly when estimating the population of daisies in a field. Which reason is correct?

  1. Random placement ensures the quadrats are placed where daisies are densest
  2. Random placement removes the need to repeat the sampling
  3. Random placement guarantees that every daisy in the field is counted
  4. Random placement avoids bias and makes the sample more representative of the whole field Correct answer.

Explanation

Random sampling reduces the chance that the student chooses areas that are unrepresentative, such as obvious flower patches, so the estimate is more reliable. It does not guarantee counting every individual or remove the need for repeats.