Ecosystems
Explain feeding relationships, follow nutrient transfers and test an ecological explanation.
Start the lesson ↓
Part 1 of 3
Read a food web
Producers convert light energy into chemical energy through photosynthesis. Consumers feed on organisms; decomposers break down organic material and release nutrients.
Food-web arrows conventionally show the direction of energy transfer from food to feeder. Removing one species can affect several connected populations.
Worked example
In a fictional web grass feeds rabbits, and rabbits feed foxes. A reduction in grass could reduce rabbit food and then fox food; the outcome also depends on alternative prey.
Common mistake: An arrow from grass to rabbit means energy moves to the rabbit.
Part 2 of 3
Distinguish nutrient cycling from energy flow
Nutrients move among organisms, litter, soil and water. Decomposition and uptake connect these stores. Energy passes through the system and is dissipated as heat; it does not cycle in the same way.
Climate affects rates of growth and decay. A large biomass store does not automatically imply a fertile soil store.
Worked example
A fictional litter store receives 12 units and loses 9 units in a month. Its net change is +3 units; the opening store is needed to calculate its final size.
Common mistake: A transfer rate is not the size of a store.
Part 3 of 3
Test a disturbance explanation
Disturbance can alter habitat, feeding relationships and nutrient pathways. A plausible cascade gives a mechanism, but observations must test its timing and alternatives.
Compare spatial coverage, climate, other species and management alongside the focal change. Use Yellowstone as a bounded example of interpreting ecological evidence.
Worked example
Fictional plant cover rises from 20% to 35% after a predator returns: +15 percentage points. A simultaneous wetter period gives an alternative influence that must be investigated.
Common mistake: A before-and-after association cannot identify a sole cause.
Try a different resource
Scatter plots
Six locations were observed once. Several unmeasured factors could influence the number of trees.
Scroll the diagram sideways to see the full resource.
| Distance (km) | Trees within 50 m |
|---|---|
| 1 | 21 |
| 2 | 12 |
| 3 | 3 |
| 4 | 3 |
| 5 | 12 |
| 6 | 21 |
Resource description
1 km: 21 trees; 2 km: 12 trees; 3 km: 3 trees; 4 km: 3 trees; 5 km: 12 trees; 6 km: 21 trees
Write an explanation
Check your answer
- Build connected mechanisms across feeding and nutrient relationships.
- Apply a defined example.
- Consider buffering or alternative pathways.
- Separate mechanism from proof of its size.
Practise and review a written answer
Case studies
Wolves and ecosystem management in Yellowstone · Desert springs in Death Valley
These pages provide selected evidence. Check the whole case requirement with your teacher.
Read further
- www.aqa.org.uk — source or course reference
- www.aqa.org.uk — source or course reference
- qualifications.pearson.com — source or course reference
- www.sqa.org.uk — source or course reference
- qualifications.pearson.com — source or course reference
- www.ocr.org.uk — source or course reference
- www.ocr.org.uk — source or course reference
- www.eduqas.co.uk — source or course reference
- www.eduqas.co.uk — source or course reference
- www.eduqas.co.uk — source or course reference
Ecosystem interdependence · Association and geographical explanations
Course links
AQA GCSE Geography · Pearson Edexcel GCSE Geography B · National 5 Geography · Pearson Edexcel GCSE Geography A · OCR GCSE Geography A · OCR GCSE Geography B · Eduqas GCSE Geography A · Eduqas GCSE Geography B · Eduqas A-level Geography
Next topics
Tropical rainforests: relationships and land-use change · Carbon cycles: stocks, fluxes and changing feedbacks
Selected teaching sequence with fictional worked data. The linked case records supply bounded evidence; they do not satisfy every course case requirement.
Scottish links identify reusable parts of the topic. Scottish landforms, soil, weather and disease requirements need additional course-specific teaching.