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IB ESS SL 2.3 Biogeochemical Cycles Questions

Trace carbon through stores and flows, calculate storage changes, explain ocean acidification and evaluate carbon-cycle mitigation evidence.

Syllabus
First assessment 2026
Course
ESS SL
Level
SL

Exam points

  • classify and interpret organic/inorganic stores, stores/sinks/sources and long-term carbon storage in cycle diagrams
  • draw, label and trace carbon-cycle stores and flows, including photosynthesis, feeding, respiration, decomposition, sequestration and mitigation pathways
  • calculate and compare carbon storage or net carbon gain between ecosystems or treatment conditions, retaining units and interpreting sink effectiveness
  • explain ocean carbon exchange and acidification by linking atmospheric CO₂, dissolution, pH change and effects on marine calcifiers
  • explain how human activities alter carbon stores and flows, then outline mitigation through reduced fossil-carbon release or increased capture and storage

Covered syllabus points

2.3.1—Biogeochemical cycles purpose2.3.2—Cycle components2.3.3—Carbon stores2.3.4—Carbon flows2.3.5—Carbon sequestration2.3.6—Ecosystems as carbon stores/sinks/sources2.3.7—Fossil fuels as carbon stores2.3.8—Agriculture as carbon store/source/sink2.3.9—Ocean carbon exchange2.3.10—Ocean acidification2.3.11—Alleviating carbon cycle impacts

Question 1

[Maximum number: 7]

Explain how a community of decomposers contributes to the stability of the whole ecosystem.

Question 2

[Maximum number: 7]
Figure 1: Carbon cycle

Figure 1: Carbon cycle

Question (a)

(a)

Identify one inorganic carbon storage in Figure 1.

[ 1 ]

Question (b)

(b)

Draw a labelled diagram to illustrate the flows of carbon between plants and the atmosphere shown in Figure 1.

[ 2 ]

Question (c)

(c)

Using the data in Figure 1, calculate the net gain in carbon in the oceans in 1015 g10^{15}\,\mathrm{g}.

[ 1 ]

Question (d)

(d)

Describe one advantage and one disadvantage of the oceans as a carbon sink.

Advantage:

Disadvantage:

[ 2 ]

Question (e)

(e)

Outline one method to mitigate the effects of atmospheric carbon storage.

[ 1 ]

Question 3

[Maximum number: 7]
Figure 1: Carbon cycle

Figure 1: Carbon cycle

Question (a)

(a)

Identify one carbon flow caused by human activities in Figure 1.

[ 1 ]

Question (b)

(b)

Draw a labelled diagram to illustrate the flows of carbon between plants and the atmosphere shown in Figure 1.

[ 2 ]

Question (c)

(c)

Using the data in Figure 1, calculate the net gain in carbon in the oceans in 1015 g10^{15}\,\mathrm{g}.

[ 1 ]

Question (d)

(d)

Describe one advantage and one disadvantage of the oceans as a carbon sink.

Advantage:

Disadvantage:

[ 2 ]

Question (e)

(e)

Outline one method to mitigate the effects of atmospheric carbon storage.

[ 1 ]
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