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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: Example of a lake ecosystem below shows an example of a lake ecosystem.

Rooting flowering plants: producers

Question (a)

(a)

State the source of energy for this ecosystem.
(a) (i) State the source of energy for this ecosystem.

[ 1 ]

Question (b)

(b)

Identify one way in which energy may leave this ecosystem.

Birds: secondary and tertiary consumer eg kingfisher

Floating plants: producers eg lilies, water fern

Frog: secondary consumer

[ 1 ]

Question (c)

(c)

Draw a food chain from the ecosystem in Figure: Example of a lake ecosystem 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 ]
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