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grass
Grass uses light to make organic material.
Class 7 · English Medium · Pearson Edexcel · General science
Living systems and ecosystems
Explain how organisms interact within a food web and a changing habitat.
Shared cross-level core and stretch unit. Start with the core questions, then use the stretch example for deeper work. The same unit is available in related class and board pathways; it is not a full grade-specific or examination-specification course. A teacher should select the appropriate depth and further topics.
Learn the idea
An ecosystem includes organisms and their physical surroundings. A food-chain arrow points from food to consumer, showing transfer of energy. Producers make organic material using an energy source; consumers feed on organisms. Decomposers return nutrients to the environment. Matter cycles, while useful energy is dissipated through transfers.
Worked example
Grass → grasshopper → frog. If a pesticide reduces grasshoppers, frogs may have less food. This is a possible effect, not a complete prediction: frogs may have alternative prey.
- Read the arrows as energy transfer.
- Identify direct and indirect relationships.
- State conditions that could change the prediction.
Stretch example
If producers store 20,000 kJ and primary consumers store 2,000 kJ over comparable areas and periods, the transfer represented is 2,000/20,000 × 100 = 10%. This is an example calculation, not a universal constant.
Your written practice
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grasshopper
The arrow runs from grasshopper to frog.
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consumer
It points in the direction of energy transfer.
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Changes in prey and competitors can spread through several links in a food web.
Describe an indirect link.
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It omits other food sources, disease, weather and movement.
Identify relevant missing mechanisms.
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10
500 ÷ 5000 × 100 = 10.
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Different areas or durations could change the totals independently of transfer efficiency.
Keep the measurement basis comparable.
Food-web explanation
Draw a local or fictional food web with six organisms.
Review with a guardian or teacher
- Label energy-transfer arrows.
- Identify producer and consumers.
- Explain one change with a stated uncertainty.
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