O-Level and SEC G3 Biology K325
B11: Organisms and their Environment
Interpret energy flow, carbon cycling, global warming, pollution, conservation, and sustainable resource use.
Reviewed for the 2027 cohort on 19 July 2026. The official syllabus remains authoritative for assessable wording and paper details.
Core notes
Organisms and their Environment links food relationships, energy transfer, the carbon cycle, global warming, pollution, conservation, and sustainable resource use. Trace each pathway from human action to ecosystem effect, and keep energy flow distinct from carbon cycling.
Food chains, webs and energy transfer
A food chain shows transfer of energy and material from a producer through consumers. Arrows point from the organism being eaten to the organism receiving energy. Food webs connect several chains and reveal how a population change can affect multiple species.
Energy decreases between trophic levels because organisms respire, move, maintain body temperature, excrete, and leave uneaten or indigestible material. Biomass and numbers often decrease at higher levels, although organism size and sampling context can affect pyramid shape.
Carbon cycle and global warming
Carbon moves among the atmosphere, organisms, decomposers, oceans, forests, and fuels. Photosynthesis removes carbon dioxide, while respiration, decomposition, and combustion return it. Forests and oceans can act as carbon sinks when they take up and retain more carbon than they release over the period considered.
Deforestation reduces carbon uptake and can release stored carbon, while fossil-fuel combustion adds carbon dioxide to the atmosphere. Higher greenhouse-gas concentrations can increase heat retention and contribute to global warming. Responses include reducing emissions, improving efficiency, protecting sinks, and using evidence to compare trade-offs.
Pollution, conservation and biodiversity
Sewage can add organic matter and microorganisms to water, increasing decomposition and reducing dissolved oxygen. Persistent plastics can entangle organisms, be ingested, and fragment in marine environments. Insecticides can enter food chains and biomagnify, exposing top carnivores to the highest concentrations.
Conservation protects species, habitats, and genetic diversity. Sustainable use allows resources to be replaced or maintained rather than depleted. Coral reefs, tropical rainforests, and mangroves provide examples where biodiversity, ecosystem services, and human livelihoods must be considered together.
Formulae and relationships
| Relationship | Use |
|---|---|
| Compare energy transfer between trophic levels. |
Worked examples
Example 1: Producers store of energy and primary consumers gain . Calculate transfer efficiency and explain why it is below .
- Divide energy transferred by energy available: .
- Multiply by to obtain .
- Energy is lost through respiration, movement, heat, excretion, and material not eaten or digested.
Answer: Transfer efficiency is , with most energy not stored as consumer biomass.
Chapter checkpoint
Use these three moves to organise the topic before attempting a mixed or practical question.
- Build food chains and webs with arrows showing energy transfer.
- Explain energy losses, pyramids, the carbon cycle, carbon sinks, and global warming.
- Trace sewage, marine plastic, or insecticide impacts and evaluate conservation and sustainable use.
Official outcome coverage
K325 B11: 9 mapped outcomes, references B11(a), B11(b), B11(c), B11(d), B11(e), B11(f), B11(g), B11(h), B11(i). Check the official K325 syllabus.
The outcome wording is not reproduced here. The relevant official syllabus remains authoritative for exact assessable scope.
Practical and data connection
Interpret energy, carbon, pollution, or biodiversity evidence with units, comparison baselines, and causal limits made explicit.
Exam traps and retrieval check
Avoid these traps
- Drawing food-chain arrows towards the organism being eaten.
- Treating energy as cycling through an ecosystem instead of flowing and dissipating.
- Naming a pollutant without explaining its pathway and biological effect.
Check from memory
What do arrows in a food chain show?
Direction of energy and material transfer.
Why can top carnivores receive high insecticide concentrations?
Persistent insecticide can biomagnify through successive trophic levels.
Name two carbon sinks in K325.
Forests and oceans.
Pure versus Combined scope
Combined Biology shares the core idea but assesses a narrower outcome set. Use the K327 or K328 component checklist to set the exact boundary.
Shared explanation source
Eclat has a related explanation in its existing IP library. It can help with the shared concept, but its IP extensions and school-sensitive scope are not automatically part of K325. Open the related IP explanation.