Question 1
Outline why an ecosystem is described as an open system.
[2]
Question 2
A woodlouse ingests fragments of dead leaves. A fungus releases digestive enzymes onto the leaves and absorbs the soluble products.
Distinguish between the feeding strategies of the woodlouse and the fungus.
[2]
Question 3
State the word equation for photosynthesis.
[1]
State the word equation for cellular respiration.
[1]
Distinguish between an energy transfer and an energy transformation in an ecosystem.
[2]
Question 4
Distinguish between an autotroph and a heterotroph.
[2]
Distinguish between the external energy sources used by photoautotrophs and chemoautotrophs.
[2]
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Question 5
Figure 1 shows the annual energy flow through four trophic levels in a grassland ecosystem. The annual energy flows are for producers, for grasshoppers, for insect-eating birds and for hawks.
Identify the trophic level containing the least annual energy flow.
[1]
Calculate the percentage efficiency of energy transfer from the grass producers to the grasshoppers.
[2]
Calculate the percentage efficiency of energy transfer from the insect-eating birds to the hawks.
[1]
Explain why the annual energy flow decreases at higher trophic levels, towards the hawks.
[2]
Question 6
During one growing season, a population of grass plants has a gross productivity of of biomass and a biomass-equivalent respiratory loss of .
Calculate the net productivity of the grass population. Show your working.
[2]
Explain why the value calculated in (a), rather than gross productivity, represents biomass potentially available to the next trophic level.
[2]
Question 7
Outline a procedure for estimating the dry plant biomass per unit area of a grassland.
[4]
Question 8
The gross primary productivity of a salt marsh is . Producer respiration is .
Calculate the net primary productivity of the salt marsh.
[2]
Explain why net primary productivity, rather than gross primary productivity, forms the renewable basis of the marsh food web.
[1]
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Question 9
The estimated net secondary productivity of a fish population is . Managers set an annual catch limit of .
State the theoretical maximum sustainable yield of the fish population.
[1]
Outline two reasons why setting the catch limit below the theoretical maximum may improve sustainability.
[2]
Question 10
Researchers measured annual energy flow through four trophic levels in a restored temperate grassland. They also measured standing biomass on one day in late summer.
Annual energy flow and late-summer standing biomass at four trophic levels in a restored temperate grassland.
| Trophic level | Energy pyramid: annual flow / | Biomass pyramid: standing crop / |
|---|---|---|
| Grasses | 18000 | 0.82 |
| Grasshoppers | 1980 | 0.061 |
| Frogs | 238 | 0.0090 |
| Snakes | 19.0 | 0.0012 |
Calculate the efficiency of energy transfer from grasses to grasshoppers.
[2]
Describe the pattern of energy flow shown in the table.
[2]
Explain why only a small proportion of the energy in the grasses reaches the snakes.
[3]
Distinguish between the information represented by the two ecological pyramids.
[2]
Evaluate the conclusion that this grassland could sustainably support an additional trophic level above the snakes.
[4]
Question 11
Part of the fictional Marula woodland was converted into a residential district. Ecologists compared ecosystem storages and flows before and after development and sampled plant biomass in the remaining woodland.
Biomass sampling and drying record for plant material from the Marula woodland.
| Measurement | Value |
|---|---|
| Number of quadrats sampled | 10 |
| Quadrat placement | Randomly positioned across the woodland |
| Area of each quadrat | |
| Plant material represented by mass records | Combined plant material from all 10 quadrats |
| Drying temperature | |
| Empty container mass | |
| Fresh sample plus container mass | |
| Mass after first drying period, container plus sample | |
| Mass after second drying period, container plus sample | |
| Mass after third drying period, container plus sample | |
| Mass after fourth drying period, container plus sample |
Calculate the dry plant biomass per square metre represented by the sample in Figure 3(b).
[2]
Explain why the sample was repeatedly dried and weighed until two consecutive masses were equal.
[2]
Analyse how urbanization has altered the storages and flows shown in Figure 3(a).
[3]
Explain how the paired diagrams illustrate that ecosystems are open systems.
[2]
Evaluate whether installing vegetated roofs throughout the residential district would restore the ecosystem energy and biomass flows shown for the intact woodland.
[4]
Question 12
Students compared plant biomass in an intact woodland and an adjacent area cleared for a road. Five randomly located quadrats were sampled at each site. Figure 2(a) summarizes the drying procedure and Figure 2(b) shows the dry plant mass obtained.
Dry plant mass from five randomly located quadrats at each site.
| Quadrat number | Intact woodland dry mass / g | Cleared area dry mass / g |
|---|---|---|
| 1 | 44 | 14 |
| 2 | 48 | 12 |
| 3 | 46 | 15 |
| 4 | 42 | 11 |
| 5 | 45 | 13 |
Outline why the samples are dried until two consecutive masses agree.
[2]
Calculate the mean dry plant biomass of the intact woodland in .
[2]
Calculate the percentage decrease in mean dry plant biomass from the intact woodland to the cleared area.
[1]
Suggest two consequences of the measured change in plant biomass for energy and matter flows at the cleared site.
[2]
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Question 13
Researchers measured the concentration of a non-biodegradable pollutant in an estuary food chain. They also measured the mean pollutant concentration in silver minnows of different ages.
Identify the organism with the greatest pollutant concentration.
[1]
Calculate how many times as great the pollutant concentration is in the marsh tern as in the silver minnow. Use for the marsh tern and for the silver minnow.
[1]
Distinguish between the processes shown in the two figures.
[2]
Explain why the pollutant concentration is greatest in the marsh tern.
[3]
Question 14
A deep-sea hydrothermal vent receives no sunlight. Figure 6(a) shows sulfide concentration and net primary productivity at increasing distances from the vent. Figure 6(b) shows part of its food web.
State the net primary productivity at from the vent.
[1]
Describe the relationship between sulfide concentration and net primary productivity.
[2]
Explain how primary production can occur in this ecosystem without sunlight.
[2]
Classify the vent crab as an autotroph or heterotroph, giving a reason from the food web.
[1]
Question 15
Figure 1 shows the concentration of a non-biodegradable pollutant in four trophic levels of an aquatic food chain.
Pollutant concentration at successive trophic levels in an aquatic food chain, listed in the direction of energy flow.
| Trophic level (food-chain order) | Pollutant concentration / mg kg |
|---|---|
| Phytoplankton | 0.03 |
| Zooplankton | 0.24 |
| Small fish | 1.8 |
| Fish-eating bird | 14.4 |
Calculate how many times as great the pollutant concentration is in the fish-eating bird as in the phytoplankton.
[2]
Explain the pattern of pollutant concentration shown in Figure 1.
[2]
Question 16
A caterpillar population ingests food at a rate of . Faecal loss is and consumer respiration is .
Calculate the gross secondary productivity of the caterpillar population.
[2]
Calculate the net secondary productivity of the caterpillar population.
[2]
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Question 17
A freshwater reservoir receives runoff from an industrial area. Researchers investigated mercury concentrations and the abundance of microplastics in its food web.
Mercury concentrations and microplastic abundance in the reservoir food web, with a lake trout age profile.
| Organism | Mercury concentration / | Microplastics / | Lake trout mercury by age / |
|---|---|---|---|
| Phytoplankton | 0.012 | Not given | Not applicable |
| Zooplankton | 0.048 | 3 | Not applicable |
| Silver minnows | 0.36 | 18 | Not applicable |
| Lake trout | 2.70 | 74 | Age 1: 0.80; age 2: 1.35; age 3: 2.05; age 4: 2.70 |
Identify the organism occupying the highest trophic level in the food chain from phytoplankton shown in Figure 2(a).
[1]
Calculate the biomagnification factor for mercury from silver minnows to lake trout.
[2]
Distinguish between bioaccumulation and biomagnification using the mercury data.
[2]
Explain how microplastics may increase the transmission of mercury through this food web.
[3]
Evaluate a proposal to reduce mercury exposure in lake trout by banning single-use plastics in settlements around the reservoir.
[5]
Question 18
An upwelling zone supports a coastal food web. Researchers measured standing biomass on one day and annual energy flow through four trophic levels.
Standing biomass and annual energy flow at four trophic levels in a coastal food web.
| Trophic level | Standing biomass / | Annual energy flow / |
|---|---|---|
| Phytoplankton | 12 | 42000 |
| Copepods | 38 | 5100 |
| Sardines | 6.4 | 560 |
| Gulls | 0.30 | 42 |
Draw a four-level food chain from the information in Figure 4(a).
[2]
Calculate the efficiency of annual energy transfer from sardines to gulls.
[2]
Explain why the pyramid of standing biomass is inverted between phytoplankton and copepods, while the pyramid of energy is not inverted.
[3]
Outline the role of decomposers in energy transformations and matter transfers in this food web.
[2]
Evaluate the claim that the low standing biomass of phytoplankton shows that this ecosystem has low productivity.
[4]
Question 19
Scientists studied a food web around a deep-sea hydrothermal vent where no sunlight reaches the seabed. Sulfur-oxidizing microorganisms form mats that are eaten by grazing snails. Mussels obtain carbon compounds from symbiotic sulfur-oxidizing microorganisms, and vent crabs eat snails and mussels.
Productivity-budget measurements for the chemoautotrophic mat and grazing-snail population.
| Budget component | Sulfur-oxidizing microbial mat / | Snail population / |
|---|---|---|
| Gross primary productivity, | 2.80 | — |
| Producer respiration, | 1.10 | — |
| Ingestion, | — | 0.62 |
| Faecal loss, | — | 0.17 |
| Consumer respiration, | — | 0.29 |
Distinguish between the nutritional classifications of the sulfur-oxidizing microorganisms and the vent crabs.
[2]
Calculate the net primary productivity of the chemoautotrophic mat.
[2]
Calculate the gross secondary productivity and net secondary productivity of the snail population.
[3]
Explain how chemoautotrophic production supports organization in the vent food web while total entropy still increases.
[3]
Evaluate whether a no-mining zone should be established around the hydrothermal vent.
[4]
Question 20
Figure 4 compares selected energy and matter storages and annual flows in a vegetated catchment before and after part of it was urbanized. Arrow widths are proportional to the flow values.
Calculate the percentage decrease in light energy converted by photosynthesis following urbanization.
[2]
Using Figure 4, state one reason why each catchment is an open system.
[1]
Explain how the energy flows shown are consistent with the first and second laws of thermodynamics.
[2]
Explain two ways in which urbanization has altered matter transfers or storages in this catchment.
[2]
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Question 21
Figure 5 shows annual carbon flows through producers and a rabbit population in one hectare of managed pasture. All flows are expressed in .
Calculate the net primary productivity of the pasture producers.
[2]
Calculate the gross secondary productivity of the rabbit population.
[1]
Calculate the net secondary productivity of the rabbit population.
[1]
State the theoretical maximum sustainable annual harvest of rabbit carbon biomass per unit area in this pasture.
[1]
Explain why net primary productivity, rather than gross primary productivity, forms the sustainable basis of the rabbit food chain.
[2]
Suggest why a manager should set the rabbit harvest below the theoretical maximum sustainable yield.
[1]
Question 22
A fishery manager estimated the net secondary productivity and recorded the harvest of a lake fish population over five years.
Estimated annual net secondary productivity, harvest and standing fish biomass over five years.
| Year | Net secondary productivity / tonnes year | Harvest / tonnes year | Standing biomass / tonnes |
|---|---|---|---|
| 1 | 35 | 30 | 360 |
| 2 | 37 | 36 | 340 |
| 3 | 40 | 43 | 300 |
| 4 | 36 | 42 | 250 |
| 5 | 29 | 35 | 210 |
State the highest estimated maximum sustainable yield and the year in which it occurred.
[2]
Identify the years in which harvest exceeded net secondary productivity.
[1]
Calculate the total amount by which harvest exceeded net secondary productivity during years 3 to 5.
[2]
Suggest why continuing a fixed quota of would be unsustainable after year 3.
[2]
Question 23
Energy and matter enter, move through and leave ecosystems. Human activities can alter these flows. Answer all parts of the following question.
Explain how photosynthesis and cellular respiration transform energy and matter in an ecosystem.
[4]
Explain why a pyramid of energy cannot be inverted and how energy transformations limit the length of food chains.
[7]
Using named examples, to what extent can reforestation restore the flows of energy and matter found in an undisturbed ecosystem?
[9]
Question 24
Distinguish between detritivores, saprotrophs, scavengers and predators as strategies for obtaining energy-containing carbon compounds.
[4]
Explain how predators and decomposers can influence the stability of energy and matter flows in a food web.
[7]
Using named examples, evaluate the reintroduction or protection of predators as a method of restoring disrupted ecosystem energy and biomass flows.
[9]
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Question 25
Figure 2 shows energy flow through three trophic levels in an agricultural ecosystem. The energy flows represented by the bars for crop plants, herbivorous insects and insect-eating birds are , and , respectively.
Calculate the ecological efficiency of energy transfer from crop plants to herbivorous insects.
[1]
Calculate the ecological efficiency of energy transfer from herbivorous insects to insect-eating birds.
[1]
Explain why producing food for humans directly from the crop plants could provide a higher sustainable yield than producing food from insect-eating birds.
[2]
Question 26
Explain how organisms can maintain highly organized structures without contradicting the second law of thermodynamics.
[3]
Question 27
A coastal fishery harvests plankton-feeding silverfish and predatory bluefin. Managers estimated annual energy flow and the productivity of both populations.
Annual energy flow through the coastal fishery food chain.
| Population | Annual energy flow / |
|---|---|
| Phytoplankton | 96000 |
| Zooplankton | 12480 |
| Silverfish | 1498 |
| Bluefin | 89.9 |
Figure 6(b): annual carbon-budget estimates, harvests and precautionary quotas for the two fish populations.
| Measure / | Silverfish | Bluefin |
|---|---|---|
| Ingestion | 6200 | 520 |
| Faecal loss | 1700 | 80 |
| Respiration | 2700 | 350 |
| Current harvest | 1350 | 126 |
| Precautionary quota | 1350 | 67.5 |
Calculate the ecological efficiency of energy transfer from silverfish to bluefin.
[2]
Using the ingestion, faecal-loss and respiration data, calculate the net secondary productivity of the silverfish population.
[3]
Determine which current harvest exceeds its estimated maximum sustainable yield.
[2]
Explain why a greater sustainable food yield is available from silverfish than from bluefin.
[3]
Evaluate the use of the precautionary quotas shown in Figure 6(b) to manage this fishery.
[4]
Question 28
Researchers estimated primary productivity in a grassland being considered for conversion to an agroforestry system. Equal plots were clipped to the same initial plant dry mass. Open plots remained in daylight, while otherwise similar plots were covered with opaque ventilated chambers.
Grassland plant carbon masses and harvest-rate comparison; grassland NPP is only a provisional proxy and is not a direct measure of agroforestry productivity.
| Measurement / context | Initial mass / | Mass after 0.50 years / | Annual rate / |
|---|---|---|---|
| Open grassland plots (median) | 0.42 | 0.71 | not measured |
| Opaque grassland plots (median) | 0.42 | 0.34 | not measured |
| Proposed agroforestry harvest (not measured) | not applicable | not applicable | 0.50 |
| Existing grassland harvest | not applicable | not applicable | 0.22 |
Calculate the net primary productivity of the open plots.
[2]
Estimate the gross primary productivity using the opaque-covered plots.
[2]
Explain three features of the method that improve the validity or reliability of the productivity estimate.
[3]
Determine whether the proposed agroforestry harvest is below the estimated maximum sustainable yield.
[2]
Evaluate whether the productivity data justify converting the grassland to harvested agroforestry.
[5]
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Question 29
A city is considering three ways of using grain produced on the same area of farmland: direct human consumption, feeding mealworms, or feeding chickens. The annual grain energy produced and the energy reaching each subsequent storage were estimated.
Annual energy transfers for three uses of grain from the same farmland area.
| Pathway | Harvested grain / | Grain consumed as feed / | New animal biomass / | Edible food energy / |
|---|---|---|---|---|
| Direct grain consumption | 1 000 000 | Not applicable | Not applicable | 650 000 |
| Mealworm production | 1 000 000 | 500 000 | 110 000 | 85 000 |
| Chicken production | 1 000 000 | 600 000 | 72 000 | 50 000 |
Classify the grain plants and mealworms by nutritional mode.
[2]
Calculate the efficiency with which consumed feed is converted into new biomass for mealworms and chickens.
[3]
Explain why direct consumption of grain provides more edible energy than either animal pathway.
[3]
Explain how the animal pathways illustrate an increase in entropy.
[2]
Evaluate the proposal that the city should replace chicken production entirely with direct grain consumption and mealworm production.
[4]
Question 30
Figure 8 compares two pathways by which the net primary production of a grain crop can provide food energy to humans. Both pathways begin with of crop net production.
Energy flows from the same crop net primary production through direct grain consumption and livestock production pathways.
| Pathway | Energy flow or store | Energy / kJ |
|---|---|---|
| Direct grain | Crop NPP | 100 000 |
| Direct grain | Edible grain to humans | 62 000 |
| Direct grain | Unharvested, processing and storage loss | 38 000 |
| Livestock | Crop NPP | 100 000 |
| Livestock | Crop energy ingested | 70 000 |
| Livestock | Crop production not ingested | 30 000 |
| Livestock | Faecal loss | 28 000 |
| Livestock | Gross secondary production | 42 000 |
| Livestock | Respiratory loss | 33 000 |
| Livestock | Net secondary production | 9 000 |
| Livestock | Processing loss | 2 000 |
| Livestock | Edible animal product to humans | 7 000 |
Calculate the ecological efficiency of the livestock between ingested crop energy and net secondary production.
[2]
Calculate how many times as much energy reaches humans through direct grain consumption as through the livestock pathway.
[1]
Distinguish between the livestock faecal loss and respiratory loss shown in Figure 8.
[2]
Explain how the livestock pathway illustrates an increase in entropy.
[1]
Using Figure 8, explain why sustainable food yields are generally higher when humans consume organisms from lower trophic levels.
[2]
Question 31
The following questions concern persistent pollutants and microplastics in aquatic food webs. Use relevant ecological terminology and named examples where requested.
Distinguish between bioaccumulation and biomagnification of a non-biodegradable pollutant.
[4]
Explain how microplastics may transmit non-biodegradable pollutants through a marine food web and affect its energy and biomass flows.
[7]
Using named examples, discuss whether preventing plastic inputs is more effective than removing plastic already present in aquatic ecosystems.
[9]
Question 32
Answer all parts about productivity and maximum sustainable yield in harvested ecosystems.
Distinguish between gross primary productivity, net primary productivity, gross secondary productivity and net secondary productivity.
[4]
Explain the relationship between net productivity, maximum sustainable yield and the long-term condition of natural capital in a harvested ecosystem.
[7]
Using named examples, evaluate the use of maximum sustainable yield as the principal basis for managing harvested ecosystems.
[9]
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Question 33
Explain the meaning of ecological efficiency and why it varies between trophic transfers.
[4]
Explain why food production for humans can generally achieve a higher sustainable yield at lower trophic levels, and why this relationship does not by itself determine whether a diet is sustainable.
[7]
Using named examples, discuss whether shifting human diets towards organisms from lower trophic levels is the most effective way to improve global food security.
[9]
Question 34
Chemoautotrophic producers can support food webs in environments with little or no light. Answer all parts about their role in ecosystems, entropy and human access.
Compare photoautotrophs and chemoautotrophs as foundations of food webs.
[4]
Explain how a food web based on chemoautotrophic primary production can maintain local organization while the total entropy of the ecosystem and its surroundings increases.
[7]
Using named examples, to what extent should human access to ecosystems dependent on chemoautotrophic production be restricted?
[9]
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