Ecology: Exam Practice

This lesson brings together all the key concepts from AQA GCSE Biology Topic 7: Ecology and focuses on how they are examined. You will review the most important content, learn command word techniques, practise structured approaches to different question types, and work through example questions with model answers.

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Key Command Words in Ecology Questions

Understanding command words is essential for answering exam questions correctly. Each command word tells you exactly what the examiner expects:

Command Word	What It Means	How to Respond
State	Give a brief, factual answer	One word or one sentence; no explanation needed
Define	Give the meaning of a term	A precise definition, using key scientific vocabulary
Describe	Say what happens or what you see	Give a detailed account but do not explain why
Explain	Say what happens and why	Give reasons using scientific knowledge
Compare	Identify similarities and/or differences	Use comparative language (e.g. "whereas", "both", "unlike")
Suggest	Apply your knowledge to an unfamiliar situation	Use your understanding to make a reasonable proposal
Evaluate	Consider the evidence and come to a conclusion, discussing strengths and weaknesses	Weigh up pros and cons; reach a supported conclusion
Calculate	Work out a numerical answer	Show your working and include units
Design	Plan an investigation	Include variables, method, equipment, and how to ensure validity

Exam Tip: Before writing your answer, underline the command word in the question. This tells you exactly what type of response is required. A "describe" question does not need explanations, and an "explain" question must include reasons, not just descriptions.

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Topic Checklist: Key Content You Must Know

Use this checklist to identify any gaps in your knowledge:

Topic Area	Key Content	Lesson
Communities and ecosystems	Biotic/abiotic factors; levels of organisation; interdependence	1
Competition	Intraspecific vs interspecific; resources competed for by plants and animals	2
Adaptations	Structural, behavioural, functional; desert/arctic examples; extremophiles	3
Organisation of ecosystems	Trophic levels; energy transfer; pyramids of biomass; decomposers	4
Sampling techniques	Quadrats; transects; capture-recapture; random sampling; population estimates	5
Carbon and water cycles	Photosynthesis, respiration, combustion, decomposition; transpiration	6
Decomposition	Factors affecting rate; Required Practical; composting; biogas	7
Biodiversity and human impact	Habitat destruction; pollution; eutrophication; deforestation; peat bogs	8
Maintaining biodiversity	Breeding programmes; seed banks; protected areas; sustainable fishing/forestry	9

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Common Exam Question Types

Type 1: Short-Answer Definitions (1-2 marks)

These questions ask you to define key terms. Be precise and concise.

Example: Define the term "ecosystem". (1 mark)

Model Answer: An ecosystem is a community of living organisms interacting with each other and with the non-living (abiotic) components of their environment.

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Type 2: Explain Questions (2-4 marks)

These questions require you to give reasons using scientific knowledge.

Example: Explain why food chains rarely have more than five trophic levels. (3 marks)

Model Answer:

• Energy is lost at each trophic level through respiration, movement and heat (1 mark)
• Only about 10% of the energy at one trophic level is transferred to the next (1 mark)
• By the fifth trophic level, there is insufficient energy remaining to support another level of consumers (1 mark)

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Type 3: Data Analysis (3-5 marks)

These questions give you data (tables, graphs or diagrams) and ask you to describe trends, calculate values or draw conclusions.

Example: A student recorded the following data from quadrat sampling:

Quadrat	1	2	3	4	5	6	7	8	9	10
Daisies	4	7	3	5	6	8	4	5	7	6

The quadrat area was 0.25 m2. The total field area was 5,000 m2.

(a) Calculate the mean number of daisies per quadrat. (1 mark)

Model Answer: Mean = (4+7+3+5+6+8+4+5+7+6) / 10 = 55 / 10 = 5.5 daisies per quadrat

(b) Estimate the total population of daisies in the field. (2 marks)

Model Answer: Population = mean per quadrat x (total area / quadrat area) = 5.5 x (5,000 / 0.25) = 5.5 x 20,000 = 110,000 daisies

Exam Tip: Always show your working in calculation questions, even if you can do the maths in your head. You can gain method marks even if your arithmetic contains an error. Always include units in your final answer.

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Type 4: Required Practical Questions (4-6 marks)

You may be asked about the method, variables, results or evaluation of the Required Practicals.

Example: Describe how you would investigate the effect of temperature on the rate of decomposition using lipase and milk. (6 marks)

Model Answer:

1. Set up water baths at five different temperatures (e.g. 10, 20, 30, 40, 50 degrees C) (1 mark)
2. Add 5 cm3 of milk and 5 cm3 of sodium carbonate solution to each test tube, along with phenolphthalein indicator (which turns pink in alkaline conditions) (1 mark)
3. Add 1 cm3 of lipase solution to each test tube and start a timer (1 mark)
4. Record the time taken for the solution to turn from pink to colourless at each temperature (1 mark)
5. Keep the volumes and concentrations of all solutions the same at each temperature (control variables) (1 mark)
6. Repeat the experiment three times at each temperature and calculate a mean to improve reliability (1 mark)

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Type 5: Extended Response / 6-Mark Questions

These questions require a detailed, well-structured answer. They often begin with "Describe and explain..." or "Evaluate..." or "Discuss...".

Structure for 6-mark answers:

graph TD
    A["Read the question carefully<br/>Underline command word"] --> B["Plan your answer<br/>(identify 3-4 key points)"]
    B --> C["Write an introduction<br/>(1 sentence)"]
    C --> D["Main body<br/>(3-4 paragraphs with<br/>scientific detail)"]
    D --> E["Conclusion<br/>(1-2 sentences<br/>summarising your answer)"]
    style A fill:#bbdefb,stroke:#1565c0
    style B fill:#c8e6c9,stroke:#2e7d32
    style C fill:#fff9c4,stroke:#f9a825
    style D fill:#ffccbc,stroke:#d84315
    style E fill:#e1bee7,stroke:#6a1b9a

Example: Discuss how human activities are reducing biodiversity and evaluate one strategy to maintain it. (6 marks)

Model Answer:

Human activities are reducing biodiversity in several ways. Deforestation removes habitats, particularly in tropical rainforests which contain the greatest diversity of species. When forests are cleared for agriculture or cattle ranching, the organisms that lived there lose their homes, food sources and breeding sites, leading to population decline and potential extinction.

Pollution also reduces biodiversity. For example, excess fertilisers from farmland can be washed into rivers, causing eutrophication. The fertilisers cause algal blooms, which block light to aquatic plants. When the plants and algae die, bacteria decompose them and use up dissolved oxygen, killing fish and other aquatic organisms.

Climate change, caused by burning fossil fuels, is altering habitats worldwide. Rising temperatures are forcing species to migrate to cooler regions, but not all species can move fast enough, leading to population decline.

One strategy to maintain biodiversity is the establishment of marine protected areas (MPAs). In MPAs, fishing and other activities are restricted, allowing fish populations to recover. This is effective because it directly addresses the cause of decline (overfishing) and allows ecosystems to regenerate. However, MPAs are difficult to enforce, especially in international waters, and they may reduce the income of local fishing communities in the short term.

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Common Mistakes to Avoid