SEC G3 Combined Science Biology component K327/K328
B9: Organisms and their Environment
Interpret energy flow, trophic losses, ecological pyramids, carbon cycling, global warming, and mitigating action.
Reviewed for the 2027 cohort on 19 July 2026. The official syllabus remains authoritative for assessable wording and paper details.
Core notes
Ecosystems cycle matter but not energy: energy enters, passes through trophic levels with losses, and eventually leaves as heating.
Food relationships and energy loss
Producers capture energy into food, consumers obtain it by feeding, and decomposers break down dead material and waste. Arrows in a food chain show the direction of energy transfer.
Energy transfer is inefficient because organisms respire, move, release heat, excrete, and leave uneaten or indigestible material. Energy therefore flows one way and less is available at successive trophic levels.
Ecological pyramids
A pyramid of numbers shows organism counts at each trophic level, so one large producer can make an inverted shape. A biomass pyramid compares total biological mass and better represents stored material at one time.
Read the labels and units before interpreting width. Number and biomass answer different questions.
Carbon sinks and global warming
Photosynthesis moves carbon into organisms, feeding transfers it, and respiration, decomposition, and combustion return carbon dioxide. Forests and oceans can remove and store carbon, acting as sinks.
Deforestation reduces carbon uptake and fossil-fuel use adds carbon dioxide, strengthening global warming. Responses include protecting forests, reducing fossil-fuel demand, improving energy efficiency, using lower-carbon energy, and changing transport or consumption, each with practical trade-offs.
Formulae and relationships
| Relationship | Use |
|---|---|
| Compare trophic energy transfer when data are given. |
Worked examples
Example 1: Why is less energy available to a secondary consumer than to the producer level?
- Producers use energy in respiration and lose heat.
- Not all plant material is eaten or digested.
- The primary consumer also uses and loses energy before being eaten.
Answer: Multiple transfers and biological processes reduce the energy passed to the secondary consumer.
Chapter checkpoint
Use these three moves to organise the topic before attempting a mixed or practical question.
- Explain Food relationships and energy loss with the named terms, evidence, and causal links kept distinct.
- Use Ecological pyramids to interpret the evidence given and justify each conclusion.
- Apply Carbon sinks and global warming to a new example, then check the conclusion against the information given.
Official outcome coverage
K327 B9: 7 mapped outcomes, references B9(a), B9(b), B9(c), B9(d), B9(e), B9(f), B9(g). Check the official K327 syllabus.
K328 B9: 7 mapped outcomes, references B9(a), B9(b), B9(c), B9(d), B9(e), B9(f), B9(g). Check the official K328 syllabus.
The outcome wording is not reproduced here. The relevant official syllabus remains authoritative for exact assessable scope.
Practical and data connection
Construct or interpret food chains, food webs, ecological pyramids and carbon-cycle data. Show the direction of energy transfer, state what each axis or area represents, and distinguish measured ecosystem evidence from a proposed mitigation effect.
Exam traps and retrieval check
Avoid these traps
- Drawing food-chain arrows towards the organism being eaten.
- Calling energy flow cyclical.
- Treating organism count and biomass as interchangeable.
Check from memory
What do food-chain arrows show?
Direction of energy transfer.
Why can a numbers pyramid be inverted?
One large organism may support many smaller consumers.
Name two carbon sinks.
Forests and oceans.
Official Combined Science scope
This shared Combined Biology owner serves both K327 and K328. Energy flow, trophic roles and transfer efficiency, ecological pyramids, carbon cycling and sinks, global warming, and mitigating action.