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IB Biology SL C4.2 Transfers of Energy and Matter Questions

Practise IB Biology SL C4.2 by tracing energy flow, nutrient cycling, biomass transfer and ecological data across trophic levels.

Syllabus
First assessment 2025
Course
Biology SL
Level
SL

Exam points

  • Define ecosystems as open systems exchanging energy and matter, and explain sunlight as the initial source converted to chemical energy by autotrophs.
  • Trace chemical energy through producers, consumers and decomposers, and construct or interpret food chains and food webs with arrows showing transfer.
  • Classify autotrophs, heterotrophs, detritivores, decomposers and saprotrophs by carbon source, energy source and digestion, including photo- versus chemoautotrophy.
  • Explain respiration as chemical-energy release producing ATP and CO2 with heat loss, and deduce trophic levels including omnivory or parasitism.
  • Construct, calculate and interpret energy pyramids and transfer efficiency using energy units, trophic labels, respiration, heat, uneaten biomass, egestion and excretion.
  • Explain why respiratory heat cannot be recycled and how inefficient energy transfer limits food-chain length and higher-level biomass.
  • Distinguish gross and net primary production, calculate productivity with units, and evaluate secondary production, feed conversion and biomass gain.
  • Construct and interpret carbon-cycle and carbon-budget evidence, identifying stores, fluxes, sinks, sources and CO2 release from biomass or fossil-fuel combustion.
  • Analyse Keeling-curve data to distinguish long-term atmospheric CO2 rise from seasonal photosynthesis and respiration oscillations.
  • Trace recycling of carbon and other elements through decomposers, inorganic nutrients and producer uptake, distinguishing matter recycling from one-way energy flow.

Covered syllabus points

C4.2.1—Ecosystems as open systemsC4.2.2—Sunlight as principal energy sourceC4.2.3—Chemical energy flowC4.2.4—Food chains and food websC4.2.5—Supply to decomposersC4.2.6—Autotrophs as self-feedersC4.2.7—Energy sourcesC4.2.8—HeterotrophsC4.2.9—Energy releaseC4.2.10—Trophic levelsC4.2.11—Energy pyramidsC4.2.12—Energy reductionsC4.2.13—Heat lossC4.2.14—Restrictions on trophic levelsC4.2.15—Primary productionC4.2.16—Secondary productionC4.2.17—Carbon cycle diagramsC4.2.18—Carbon sinks and sourcesC4.2.19—CO₂ release during combustionC4.2.20—Keeling Curve analysisC4.2.21—Dependence between respiration and photosynthesisC4.2.22—Recycling of all chemical elements

Question 1

[Maximum number: 6]

Describe the movement of energy and nutrients in an ecosystem.

Question 2

[Maximum number: 7]

Compounds of carbon, hydrogen and oxygen are used to supply and store energy.

Explain how the energy supply in an ecosystem is dependent on sunlight.

Question 3

[Maximum number: 4]

The mass of an individual organism can affect its physiology and feeding ecology. The diagram shows the relative mass of carbon (black) and total wet mass (grey) of a marine crustacean, Calanus hyperboreus and a jellyfish, Bathocyroe fosteri.

Figure for Question 3 — IB Biology SL

Question (a)

(a)

State one process that results in the loss of carbon dioxide from a marine organism such as a crustacean or a jellyfish.

[ 1 ]

Question (b)

(b)

Explain how energy enters, flows through and is lost from marine food chains.

Figure for Question (b) — IB Biology SL
[ 3 ]
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