IB ESS HL 2.3.1 Biogeochemical Cycles Question Bank
Explain why matter cycles through living, geological and atmospheric stores in ecosystems.
- Syllabus
- First assessment 2026
- Course
- ESS HL
- Level
- HL
Exam points
- identify the relevant store, flow or process
- trace matter through the biogeochemical cycle
- evaluate the ecological or climate consequence of the change
2.3.1—Biogeochemical cycles purpose question 1
[Maximum number: 7]
Explain how a community of decomposers contributes to the stability of the whole ecosystem.
Explain how a community of decomposers contributes to the stability of the whole ecosystem
a. Decomposers will feed on dead organic matter/detritus (like dead leaves, wood, carcasses, feces)...;
b. ... reducing their accumulation / cleaning up Earth;
c. They will break down organic matter into inorganic matter…;
d. ...enhancing soil fertility / increasing nutrient availability;
e. The inorganic minerals (nitrates, phosphates, metals) will then feed plant communities / will be absorbed by plant roots...;
f. ...supporting high vegetation/plant abundance;
g. ...and may support high habitat/niche diversity;
h. Decomposers are responsible for nutrient cycling / e.g. nitrogen cycling (nitrogen fixation/ammonification/nitrification/denitrification/phosphorus cycling/carbon cycle;
i. ...high flow of matter may support complex food webs;
j. Decomposers are the basis of a detritus-based food web / important part of ecosystem flow of energy / may be eaten/pass biomass on to carnivore community...; k. ...supporting/stabilizing carnivore abundance;
I. As decomposer numbers decrease due to predation, so do carnivores;
m. ... thereby contribute to regulation of the carnivore community / which is an example of negative feedback (leading to stability); n. Decomposer will release organic matter through their own death/defecation...; o. ... which would provide food for other decomposers; p. Decomposers participate in humus formation...; q. ...increasing water holding capacity of soil (and soil fertility = MPd); r. Decomposers may compete with one another regulating their populations (another example of negative feedback = MPm); s. Decomposers, like earthworms, loosen soil / disperse nutrients / create space for air and water circulation...; t. ...helping root growth / improving soil structure; u. Fragmentation: larger invertebrates initially fragment larger chunks of organic matter (then bacteria and fungi complete decomposition into nutrients = MPc);
v. After a disturbance, decomposers will increase their metabolic/respiration rate/feeding on detritus...;
w. ...contributing to a faster return to original state (resilience entailing stability);
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