ESAT Biology: Ecosystems and plant physiology, set 1

• Answer all questions. No calculator.
• Each question has exactly one correct answer.
• Work only with the values given in each question; no calculator is allowed or needed.

1. 11 mark

   Which sequence correctly lists the levels of biological organisation within an ecosystem, from smallest to largest?

   1. A Organism, population, community, ecosystem
   2. B Population, organism, community, ecosystem
   3. C Organism, community, population, ecosystem
   4. D Community, population, organism, ecosystem
2. 21 mark

   Clownfish live among the stinging tentacles of a sea anemone. The clownfish gains protection from predators that cannot tolerate the anemone's sting, while the anemone benefits from scraps of food dropped by the clownfish and from improved water circulation around its tentacles as the fish swims. Which term best describes this relationship between the two species?

   1. A Parasitism, because the clownfish benefits from the anemone's protection without giving anything back
   2. B Competition, because both species are competing for the same food and living space on the reef
   3. C Predation, because the anemone's tentacles could sting and kill the clownfish if the relationship broke down
   4. D Mutualism, because both species gain a benefit from living together
3. 31 mark

   A population of deer numbers 800 individuals in year 1. In year 2, an outbreak of a parasitic disease, a biotic factor, causes the population to fall by 25%. In year 3, the disease causes a further fall of 20% of the year 2 population. What is the deer population in year 3?

   1. A 320
   2. B 600
   3. C 440
   4. D 480
4. 41 mark

   Carbon moves between the atmosphere and living organisms as part of the carbon cycle. Which of the following processes does NOT add carbon dioxide to the atmosphere?

   1. A Decomposition of dead organisms by microorganisms
   2. B Photosynthesis by green plants and algae
   3. C Respiration by animals and plants
   4. D Combustion of fossil fuels such as coal and oil
5. 51 mark

   Which statement correctly describes a stage of the water cycle and explains its importance to living organisms?

   1. A Precipitation falls only over the oceans, so the water cycle mainly benefits marine organisms and has little importance for organisms living on land
   2. B Rivers flowing into the sea are the whole of the water cycle; evaporation from oceans and plants, and condensation in the atmosphere, play no part in it
   3. C Water evaporates from oceans and other surfaces and transpires from plants, then condenses in the atmosphere and falls as precipitation over land, renewing the fresh water land organisms need
   4. D Water vapour condenses directly into rivers, which then evaporate into rain clouds that fall as precipitation, providing organisms with a constant supply of carbon dioxide dissolved in rainwater
6. 61 mark

   Decomposers such as bacteria and fungi break down dead organisms and waste material as part of the carbon cycle. Which gas is released as a direct result of the decomposers' own respiration during this process, returning carbon to the atmosphere?

   1. A Carbon dioxide, released as decomposers respire while breaking down the dead material
   2. B Nitrogen gas, released directly from the proteins in the dead organism as it decays
   3. C Glucose, released back into the soil as the dead organism's stored sugars are broken down
   4. D Oxygen, released as decomposers photosynthesise while breaking down dead material
7. 71 mark

   A student wants to estimate the total number of daisies growing in a rectangular field measuring 50 m by 20 m. Ten 1 m by 1 m quadrats are placed at random positions in the field, and a total of 84 daisies are counted across all ten quadrats. What is the best estimate of the total number of daisies in the whole field?

   1. A 84000
   2. B 84
   3. C 840
   4. D 8400
8. 81 mark

   A student wants to find out whether the percentage cover of a moss species changes with distance from a riverbank. Which method is most appropriate for investigating this, and why?

   1. A Lay a tape measure in a line away from the riverbank, and record the percentage cover of moss in a quadrat placed at regular intervals along it
   2. B Place ten quadrats at random positions across the whole study area, then average the percentage cover recorded in each quadrat
   3. C Record only whether moss is present or absent in a single quadrat placed at the riverbank, rather than sampling at increasing distances away from it
   4. D Place one quadrat at the riverbank and one quadrat as far from the riverbank as possible, then compare only these two counts
9. 91 mark

   Fertiliser washed from farmland into a lake causes rapid growth of algae on the water's surface. When the algae die, they are broken down by aerobic bacteria, and soon afterwards many of the lake's fish are found dead. Which term describes this process, and what is the main reason the fish die?

   1. A Bioaccumulation; the fish die because they directly ingest fertiliser chemicals, which build up to toxic levels in their tissues over time
   2. B Eutrophication; the fish die mainly because the thick algae layer blocks sunlight, and the resulting build-up of carbon dioxide directly poisons the fish
   3. C Acid rain deposition; the fish die because pollutant gases dissolve in the lake and lower its pH until the water is too acidic for the fish to survive
   4. D Eutrophication; the fish die because there is too little dissolved oxygen left in the water for them to survive
10. 101 mark

    Photosynthesis is described as an endothermic reaction. Which statement correctly explains why this description applies?

    1. A It transfers light energy into chemical energy, which becomes stored in the bonds of the glucose molecules produced
    2. B It requires no external source of energy at all, since the reaction occurs spontaneously within the chloroplast
    3. C It breaks down glucose using oxygen to release the chemical energy that was stored within it, which is what respiration does
    4. D It releases energy to the surroundings as heat, and this heat energy is used to form new chemical bonds in glucose
11. 111 mark

    Which word equation correctly represents the overall process of photosynthesis?

    1. A glucose + water, using light energy, produces carbon dioxide + oxygen
    2. B glucose + oxygen, using light energy, produces carbon dioxide + water
    3. C carbon dioxide + oxygen, using light energy, produces glucose + water
    4. D carbon dioxide + water, using light energy, produces glucose + oxygen
12. 121 mark

    In an experiment on pondweed, the rate of photosynthesis is measured at increasing light intensities, while temperature and carbon dioxide concentration are both kept constant at low levels throughout. The rate of photosynthesis rises steadily as light intensity increases at first, but beyond a certain light intensity, further increases produce no further rise in rate. Which explanation best accounts for this plateau?

    1. A Chlorophyll in the pondweed has been permanently destroyed by the light used in the experiment, preventing any further increase in rate
    2. B Carbon dioxide concentration, or temperature, which was kept low and constant while light intensity kept rising, has become the limiting factor
    3. C Light intensity itself becomes the limiting factor throughout the experiment, so the plateau is caused directly by there being too much light
    4. D The pondweed has run out of water to take up through its cut stem, so no further photosynthesis is possible no matter how much light is provided
13. 131 mark

    Which statement correctly distinguishes the structure and function of xylem from phloem in a plant?

    1. A Xylem transports water only downward, from the leaves to the roots, while phloem transports sugars only upward, from the roots to the leaves
    2. B Xylem is lignified dead cells carrying water and mineral ions from the roots to the stem and leaves; phloem is living cells carrying dissolved sugars from the leaves to the rest of the plant
    3. C Xylem consists of living cells that transport dissolved sugars from the leaves to the rest of the plant; phloem consists of lignified dead cells that transport water and mineral ions from the roots to the stem and leaves
    4. D Both xylem and phloem are made of lignified dead cells, but xylem transports sugars produced in the leaves while phloem transports water and mineral ions from the roots
14. 141 mark

    A potometer is used to estimate the rate of transpiration of a leafy shoot. Over 4 minutes, the air bubble in the potometer's capillary tube moves a distance that corresponds to 0.6 cm^3 of water taken up by the shoot. What is the rate of transpiration, in cm^3 of water per minute?

    1. A 2.4 cm^3 per minute
    2. B 0.6 cm^3 per minute
    3. C 6.7 cm^3 per minute
    4. D 0.15 cm^3 per minute
15. 151 mark

    Which combination of environmental conditions would produce the HIGHEST rate of transpiration from a leafy shoot?

    1. A Bright light, still air, high humidity, low temperature
    2. B Bright light, moving air, low humidity, high temperature
    3. C Bright light, still air, low humidity, high temperature
    4. D Dim light, still air, high humidity, low temperature

Worked solutions

Every question below carries the reasoning, not just the answer. The official material for this test publishes a correct option letter and nothing else.

1. Question 1Answer: A

   1. The levels of organisation build up from the smallest unit to the largest: an organism is a single individual living thing.
   2. A population is all the organisms of one species living in the same area at the same time, so it is built from many organisms.
   3. A community is all the different populations (of different species) living and interacting in the same area.
   4. An ecosystem is a community together with the non-living, abiotic parts of its environment, such as soil, water and climate, so it is the largest and most inclusive level.
   5. Putting these together from smallest to largest gives organism, population, community, ecosystem, so A is correct.
   • Why not B: Reverses the first two levels. A population is a group of individual organisms of one species, so it is built from organisms, not the other way round.
   • Why not C: Swaps community and population. A community is made up of the different populations living in a habitat, so population must come before community, not after it.
   • Why not D: Lists the units almost entirely backwards, starting from a group of populations before reaching the single organism that all the higher levels are ultimately built from.

2. Question 2Answer: D

   1. Interdependence describes relationships between species living in a community, including predation, mutualism and parasitism.
   2. Predation is where one organism, the predator, kills and eats another, the prey. That is not happening here, since neither organism kills the other.
   3. Parasitism is where one organism benefits and the other is harmed, or at least gains nothing. The passage states the anemone gains benefits too, so this does not fit.
   4. Mutualism is where both organisms in the relationship benefit: here, the clownfish gains protection and the anemone gains food scraps and better water flow.
   5. Since both species benefit, the relationship is mutualism, so D is correct.
   • Why not A: Names parasitism, which describes one species benefiting at the expense of the other. The passage states the anemone also benefits, which parasitism does not allow for.
   • Why not B: Names competition, which applies when two species need the same limited resource. The clownfish and anemone are not shown competing for anything; they are cooperating.
   • Why not C: Names predation, but predation means one organism kills and eats another. Neither species is killed or eaten by the other in this relationship.

3. Question 3Answer: D

   1. A biotic factor is a living factor, such as disease, predation or competition, that affects population size; this disease outbreak is one example.
   2. The year 2 population is 800 reduced by 25%: 800 x 0.75 = 600.
   3. The year 3 fall is 20% of the year 2 population, 600, not of the original 800, so the fall is 600 x 0.2 = 120.
   4. The year 3 population is therefore 600 minus 120, which is 480.
   5. So the correct answer is D, 480.
   • Why not A: Adds the two amounts by which the population fell, 200 in year 2 and 120 in year 3, to get 320, but this is the total decrease, not the population that remains.
   • Why not B: Stops after applying only the year 2 fall (800 x 0.75 = 600) and never applies the further fall in year 3 at all.
   • Why not C: Applies the year 3 fall of 20% to the original 800 (giving 160) instead of to the reduced year 2 population of 600 (which would give 120), so it subtracts the wrong amount.

4. Question 4Answer: B

   1. The carbon cycle moves carbon between the atmosphere, as carbon dioxide, and living organisms.
   2. Respiration, combustion and decomposition all release carbon dioxide into the atmosphere as a product of breaking down organic or fossil carbon compounds.
   3. Photosynthesis works in the opposite direction: it uses light energy to react carbon dioxide with water, removing carbon dioxide from the atmosphere and locking the carbon into glucose.
   4. So the one process listed that does NOT add carbon dioxide to the atmosphere is photosynthesis, making B correct.
   • Why not A: Decomposers respire as they break down dead material, releasing carbon dioxide in the process, so decomposition also adds carbon dioxide rather than avoiding it.
   • Why not C: Respiration releases carbon dioxide as a waste product of breaking down glucose, so it adds carbon dioxide to the atmosphere rather than avoiding it.
   • Why not D: Burning fossil fuels releases the carbon they have stored for millions of years as carbon dioxide, so it is one of the main processes adding carbon dioxide to the atmosphere.

5. Question 5Answer: C

   1. The water cycle moves water between the oceans, the atmosphere and land through evaporation, transpiration, condensation and precipitation.
   2. Water evaporates from oceans, lakes and rivers, and also leaves plants by transpiration, entering the atmosphere as water vapour.
   3. This water vapour cools and condenses into clouds, and eventually falls back to Earth as precipitation, including over land.
   4. This constant replenishment of fresh water over land is what allows land organisms to drink, and allows plants to take up the water they need for photosynthesis and transport.
   5. So C correctly describes the cycle and its importance.
   • Why not A: Wrongly claims precipitation falls only over oceans. In reality a large share of precipitation falls over land, which is exactly why land organisms depend on the water cycle for fresh water.
   • Why not B: Claims river flow to the sea is the whole cycle, but that leaves out evaporation and condensation, the very stages that carry water from the sea back over land as fresh precipitation.
   • Why not D: Reverses the order of evaporation and condensation, and confuses the water cycle's importance, providing fresh water, with the carbon cycle's role in moving carbon dioxide.

6. Question 6Answer: A

   1. Decomposers, like all living organisms, respire to release energy from the organic material they feed on.
   2. Aerobic respiration in the decomposers produces carbon dioxide as a waste product, in the same way it does in any other organism.
   3. This carbon dioxide is released into the atmosphere, which is how the carbon locked up in dead organisms is returned to the air as part of the carbon cycle.
   4. So the gas released is carbon dioxide, making A correct.
   • Why not B: Names nitrogen gas, which belongs to the separate nitrogen cycle. This question is about carbon returning to the atmosphere, which happens through carbon dioxide, not nitrogen gas.
   • Why not C: Names glucose, but glucose is a solid, energy-storing molecule that respiration breaks down, not a gas that is released to the atmosphere.
   • Why not D: Names oxygen, but oxygen is a product of photosynthesis. Decomposers such as bacteria and fungi do not photosynthesise; they respire, like other living organisms.

7. Question 7Answer: D

   1. Each quadrat covers 1 m by 1 m, which is 1 square metre, and ten quadrats were used, so the total area sampled is 10 square metres.
   2. The mean number of daisies per quadrat, per square metre, is the total count divided by the number of quadrats: 84 divided by 10 is 8.4 daisies per square metre.
   3. The whole field has an area of 50 m by 20 m, which is 1000 square metres.
   4. The estimated total population is the mean density multiplied by the total area: 8.4 x 1000 = 8400.
   5. So the best estimate is 8400 daisies, making D correct.
   • Why not A: Skips finding the mean number of daisies per quadrat and instead treats the total of 84, from all ten quadrats put together, as if it were the count in a single square metre, overestimating by a factor of ten.
   • Why not B: Uses the raw total count from the quadrats as the estimate for the entire field, without scaling up from the small sampled area, 10 square metres, to the field's full area, 1000 square metres, at all.
   • Why not C: Scales up using the wrong field area, effectively reading the field as 10 m by 10 m, 100 square metres, rather than the stated 50 m by 20 m, 1000 square metres, so the estimate is ten times too small.

8. Question 8Answer: A

   1. The question is about how an organism's abundance changes along a gradient, increasing distance from the riverbank, not simply what the average abundance is.
   2. A belt transect is the method designed for this: a line is marked out along the gradient of interest, and a quadrat is used to sample percentage cover at set intervals along that line.
   3. This produces a set of percentage cover readings, each linked to a known distance from the riverbank, allowing a pattern, or lack of one, to be identified.
   4. So laying a tape measure away from the riverbank and sampling at regular intervals, as in A, is the appropriate method.
   • Why not B: Places quadrats randomly across the whole area, which is suited to estimating an overall average abundance, but random positions are not linked to distance from the riverbank, so this cannot show how cover changes along that gradient.
   • Why not C: Uses a single quadrat at a single location, so there is no way to compare how cover differs at different distances, and recording only presence or absence discards the percentage cover data needed to see a change.
   • Why not D: Samples only the two most extreme points and ignores everywhere in between, so the pattern of change across the gradient, for example whether it changes gradually or sharply, cannot be determined.

9. Question 9Answer: D

   1. Excess fertiliser, nitrates and phosphates, washing into water causes algae to grow rapidly; this process is called eutrophication.
   2. The algae eventually die, and aerobic bacteria and other decomposers break down the dead algae, respiring as they do so.
   3. This respiration by the huge numbers of decomposers uses up much of the dissolved oxygen in the water.
   4. With too little dissolved oxygen left, fish and other aquatic organisms that need it for their own respiration suffocate and die.
   5. So the process is eutrophication, and the fish die from a lack of dissolved oxygen, making D correct.
   • Why not A: Names bioaccumulation, which describes a toxin building up in an organism's body and increasing further up a food chain. The scenario describes decomposition using up oxygen, not fish absorbing a toxin directly.
   • Why not B: Correctly names eutrophication, but gives the wrong cause of death: it is oxygen depletion by the respiring decomposers that kills the fish, not carbon dioxide poisoning from blocked sunlight.
   • Why not C: Describes acid rain lowering the lake's pH, a different pollution pathway entirely. The scenario describes fertiliser run-off causing algal growth, which is eutrophication, not acidification.

10. Question 10Answer: A

    1. An endothermic reaction is one that takes in energy from its surroundings overall, rather than releasing it.
    2. In photosynthesis, light energy is absorbed by chlorophyll and used to drive the reaction between carbon dioxide and water.
    3. This light energy is converted into chemical energy, which ends up stored in the bonds holding together the glucose molecules that are produced.
    4. Because energy is taken in, as light, and stored in the product rather than released, photosynthesis is endothermic, making A correct.
    • Why not B: Claims no external energy source is needed, but photosynthesis is endothermic precisely because it needs an external energy input, light energy, to proceed. It is not spontaneous without it.
    • Why not C: Describes glucose being broken down to release energy, which is what happens in respiration. Photosynthesis is the reverse process, building glucose up and storing energy in it.
    • Why not D: Describes energy being released as heat to the surroundings, which is what an exothermic reaction does. An endothermic reaction absorbs energy from the surroundings instead.

11. Question 11Answer: D

    1. Photosynthesis uses light energy to react two simple raw materials, carbon dioxide and water, taken in by the plant.
    2. These combine to produce glucose, which the plant stores or uses, and oxygen, which is released as a by-product.
    3. So the correct word equation is: carbon dioxide plus water, using light energy, produces glucose plus oxygen.
    4. This matches option D.
    • Why not A: Uses glucose as a reactant instead of a product, and pairs it with water on the wrong side of the equation, when water should be a reactant alongside carbon dioxide.
    • Why not B: Places glucose and oxygen on the reactants side and carbon dioxide and water on the products side. This is the word equation for respiration, the reverse of photosynthesis.
    • Why not C: Uses oxygen as a reactant instead of water. Oxygen is a product of photosynthesis, released as a by-product, not something the plant takes in for this reaction.

12. Question 12Answer: B

    1. In a limiting factor experiment, the rate of a process is controlled by whichever required factor is in shortest supply at that moment.
    2. As light intensity increases from a low level, it is initially the limiting factor, so the rate of photosynthesis rises as light intensity rises.
    3. Once light is no longer in short supply, some other factor being held constant and low, here carbon dioxide concentration or temperature, becomes the new limiting factor instead.
    4. From that point on, increasing light intensity further cannot increase the rate, because the reaction is now limited by the constant low level of carbon dioxide or temperature, producing the observed plateau.
    5. So B is the correct explanation.
    • Why not A: Suggests the light itself has destroyed the chlorophyll, but the light intensities used in a standard limiting-factor experiment are not high enough to damage chlorophyll, and no such damage is described.
    • Why not C: Claims light intensity is still the limiting factor at the plateau, but if that were true, increasing light intensity further would keep increasing the rate. The plateau shows the rate has instead become limited by something else.
    • Why not D: Introduces water shortage as the cause, but the experiment does not mention or vary water availability, so there is no basis in the scenario for blaming a lack of water.

13. Question 13Answer: B

    1. Xylem tissue is made of lignified, strengthened, dead cells, joined end to end to form continuous tubes.
    2. These dead xylem cells transport water and dissolved mineral ions upward, from the roots, where they are absorbed, to the stem and leaves, where they are needed.
    3. Phloem tissue, in contrast, is made of living cells, which is necessary because loading sugars into the phloem requires active transport, a living process.
    4. Phloem transports dissolved sugars, mainly produced by photosynthesis in the leaves, to other parts of the plant that need them, such as growing tissues and storage organs.
    5. So B correctly describes both the structures and the functions of xylem and phloem.
    • Why not A: Reverses the direction of water movement in the xylem, which actually carries water upward, from the roots to the stem and leaves, not downward from the leaves to the roots.
    • Why not C: Swaps the two tissues completely. It is xylem that is made of lignified dead cells carrying water and minerals, and phloem that is made of living cells carrying dissolved sugars, not the other way round.
    • Why not D: Wrongly describes phloem as being made of lignified dead cells like xylem. Phloem is made of living cells, which is essential since active transport is involved in loading sugars into it.

14. Question 14Answer: D

    1. The rate of transpiration is defined as the volume of water taken up divided by the time taken.
    2. Here, the volume of water taken up is 0.6 cm^3, and the time over which this was measured is 4 minutes.
    3. Rate = volume / time = 0.6 cm^3 / 4 minutes = 0.15 cm^3 per minute.
    4. So the rate of transpiration is 0.15 cm^3 per minute, making D correct.
    • Why not A: Multiplies the volume by the time instead of dividing, which increases rather than reduces the figure, giving a rate far larger than the volume measured.
    • Why not B: Reports the total volume of water taken up, 0.6 cm^3, as if it were already the rate, without dividing by the 4 minutes over which that volume was measured.
    • Why not C: Divides the time by the volume instead of the volume by the time, inverting the rate calculation.

15. Question 15Answer: B

    1. The rate of transpiration is increased by higher light intensity, which opens stomata wider, greater air movement, which removes water vapour from around the leaf and maintains a steep diffusion gradient, lower humidity, which also steepens the diffusion gradient out of the leaf, and higher temperature, which increases the kinetic energy and evaporation rate of water molecules.
    2. Option B combines all four of these conditions in the direction that increases transpiration: bright light, moving air, low humidity and high temperature.
    3. Every other option is missing at least one of these four conditions, or has one of them working in the opposite direction, so each produces a lower rate than B.
    4. So the highest rate of transpiration is produced by the conditions in B.
    • Why not A: Bright light does increase transpiration by opening stomata wider, but still air, high humidity and low temperature all work against a high rate, so the combination as a whole does not maximise transpiration.
    • Why not C: Gets light, humidity and temperature right for a high rate, but leaves out air movement: still air allows water vapour to build up just outside the leaf, reducing the diffusion gradient and lowering the rate compared with moving air.
    • Why not D: Combines dim light, still air, high humidity and low temperature, each of which independently reduces the rate of transpiration, so this gives the lowest rate of the four options, not the highest.