CourseCourseConceptConcept

IB ESS SL 2.2 Energy and Biomass in Ecosystems Questions

Trace energy through food chains and food webs, interpret productivity and biomass evidence, and explain losses and pollutant transfer.

Syllabus
First assessment 2026
Course
ESS SL
Level
SL

Exam points

  • trace energy transformations from sunlight through producer biomass and trophic transfers to heat, explaining conservation and respiration losses
  • interpret food chains and food webs by identifying trophic levels, arrow direction, decomposer pathways, multiple feeding positions and population cascades after species or human-pressure changes
  • explain and calculate gross and net productivity from energy, biomass, respiration and faecal-loss data, then interpret units, environmental controls and productivity contrasts
  • measure and interpret biomass and ecological pyramids by selecting dry-mass or sampling methods, using appropriate units, and explaining inverted, changing or data-limited shapes
  • explain organic-matter and energy losses between trophic levels by distinguishing unharvested, uneaten, unabsorbed, metabolic-waste and respiratory losses, and use these losses to explain limits on food-chain length
  • distinguish persistence, bioaccumulation and biomagnification, then interpret pollutant concentrations and risks to higher-trophic-level organisms and human food chains

Covered syllabus points

2.2.1—Ecosystem sustenance2.2.2—First law of thermodynamics2.2.3—Energy and matter transformation2.2.4—Photosynthesis2.2.5—Producers2.2.6—Cellular respiration2.2.7—Heat generation2.2.8—Second law and energy loss2.2.9—Consumer energy sources2.2.10—Producers and food chains2.2.11—Food chains and trophic levels2.2.12—Food-chain energy losses2.2.13—Gross and net productivity2.2.14—Limits on trophic levels2.2.15—Food webs2.2.16—Biomass measurement2.2.17—Ecological pyramids2.2.18—Non-biodegradable pollutants2.2.19—Microplastics2.2.20—Human activity impacts

Question 1

[Maximum number: 3]
Figure: Example of a lake ecosystem

Figure:Example of a lake ecosystem

Figure 1 shows an example of a lake ecosystem.

Rooting flowering plants: producers
Birds: secondary and tertiary consumer eg kingfisher
Floating plants: producers eg lilies, water fern
Frog: secondary consumer

Question (a)

(a)

State the source of energy for this ecosystem.

[ 1 ]

Question (b)

(b)

Identify one way in which energy may leave this ecosystem.

[ 1 ]

Question (c)

(c)

Draw a food chain from the ecosystem in Figure 1 consisting of four trophic levels.

[ 1 ]

Question 2

[Maximum number: 7]

Compare and contrast the pathways of energy through the atmosphere and the pathways of energy through an ecosystem.

Question 3

[Maximum number: 11]

Question (a)

(a)

Outline the transfers and transformations of matter as it enters and flows through the first trophic level of a food chain.

[ 4 ]

Question (b)

(b)

Describe how the emissions from the combustion of fossil fuels may impact the productivity of terrestrial ecosystems.

[ 7 ]

Question 4

[Maximum number: 1]
Figure: Example of a lake ecosystem

Figure:Example of a lake ecosystem

Figure 1 shows an example of a lake ecosystem.

Rooting flowering plants: producers
Birds: secondary and tertiary consumer eg kingfisher
Floating plants: producers eg lilies, water fern
Frog: secondary consumer

State the source of energy for this ecosystem.

Question 5

[Maximum number: 4]

Outline the transfers and transformations of matter as it enters and flows through the first trophic level of a food chain.

Question 6

[Maximum number: 4]

Outline the transfers and transformations of energy as it enters and flows through the first trophic level of a food chain.

Question 7

[Maximum number: 4]

Describe the role of primary producers in ecosystems.

Question 8

[Maximum number: 2]
Figure 5: Coastal seawater temperature near a nuclear power station

Figure:Coastal seawater temperature near a nuclear power station

Figure 5 shows a range of coastal seawater temperatures at different distances from a nuclear power station. Nuclear power stations may be responsible for localized thermal pollution of coastal waters. Thermal pollution is caused by warmer water being released into a colder body of water.

Thermal pollution lowers the dissolved oxygen content of water.

Suggest the effect of this on a named transformation process.

Question 9

[Maximum number: 1]
Figure: Example of a lake ecosystem

Figure:Example of a lake ecosystem

Figure 1 shows an example of a lake ecosystem.

Rooting flowering plants: producers
Birds: secondary and tertiary consumer eg kingfisher
Floating plants: producers eg lilies, water fern
Frog: secondary consumer

Identify one way in which energy may leave this ecosystem.

Question 10

[Maximum number: 2]
Figure for Question 10 — IB ESS SL

The diagram shows gross and net productivity at different trophic levels in the Silver Springs, Florida, ecosystem.

Describe how the second law of thermodynamics operates in relation to the transfer of energy within the Silver Springs ecosystem.

Question 11

[Maximum number: 1]
Energy flow through an ecosystem

Figure:Energy flow through an ecosystem

Figure 7 shows the energy flow in an ecosystem. The width of the arrows is proportional to the quantity of energy transferred.

With reference to Figure 7,

State the group of organisms at C that feed on dead plants, animals and feces.

Question 12

[Maximum number: 1]
Figure A simplified food web in a kelp forest ecosystem

Figure A simplified food web in a kelp forest ecosystem

Figure Kelp forest ecosystems with and without the presence of sea otters

Figure Kelp forest ecosystems with and without the presence of sea otters

The arrows indicate the flow of carbon between the atmosphere and the carbon stored in kelp.

State the trophic level of sea urchins in the kelp forest ecosystem shown in Figure.

Question 13

[Maximum number: 7]

Explain the ways in which energy is lost as it moves through an ecosystem.

Question 14

[Maximum number: 7]

Define the terms gross primary productivity (GPP) and net primary productivity (NPP). Explain, with reference to two contrasting biomes, why one biome will be more productive than the other.

Question 15

[Maximum number: 1]
Figure 10(b): Simplified food web for Mindo cloud forest

Figure:Simplified food web for Mindo cloud forest

Outline one impact that a reduction in the Mindo harlequin toad population may have on the food web in Figure 10(b).

Question 16

[Maximum number: 3]

Describe how biomass data from a named biome could be collected.

Question 17

[Maximum number: 7]

Explain why pyramids of numbers, biomass and productivity may vary in shape for different food chains.

Question 18

[Maximum number: 4]

Outline two advantages and two disadvantages of using DDT.

Question 19

[Maximum number: 1]
Figure: Dead albatross chick with plastic garbage in stomach

Figure:Dead albatross chick with plastic garbage in stomach

Figure:Albatross and plastic impacts

- Figure: Albatross and plastic impacts: larger plastic pieces are taken in by fish, sea birds and animals, which may die of starvation.
- One study estimates around 1 million sea birds, including albatrosses, and 100000 animals are killed by ingestion of plastic or entanglement in plastic fishing nets.
- About half of all albatross species are endangered or critically endangered on the Red List.

Explain why albatross chicks may starve if they eat plastic.

Question 20

[Maximum number: 7]

Describe how the emissions from the combustion of fossil fuels may impact the productivity of terrestrial ecosystems.

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