Ecosystems and Interdependence
Ecosystems and interdependence is the study of how living organisms interact with each other and with the non-living parts of their environment within a habitat. It covers food chains, food webs, energy transfer between trophic levels, adaptations for survival, and required practical sampling methods such as quadrats.
Method
- Learn key vocabulary: habitat, population, community, ecosystem and niche.
- Classify factors affecting organisms as biotic (living) or abiotic (non-living).
- Build food chains and food webs, identifying producers, consumers and decomposers.
- Practise energy transfer calculations between trophic levels using the 10% rule.
- Learn the required practical methods for sampling organisms, including quadrats and capture-mark-recapture.
- Explain how structural, behavioural and physiological adaptations help organisms survive and compete.
Worked example
A student uses capture-mark-recapture to estimate the population of woodlice in a garden. On day 1 she catches and marks 40 woodlice, then releases them. On day 2 she catches 50 woodlice, of which 8 are marked. Estimate the total population of woodlice in the garden.
- Write down the capture-mark-recapture formula: estimated population = (number marked first time x total caught second time) / number marked second time.
- Substitute the values: (40 x 50) / 8.
- Calculate the numerator: 40 x 50 = 2000.
- Divide: 2000 / 8 = 250.
- State the final answer: estimated population = 250 woodlice.
Practice questions
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Q1Define the term habitat.Show answer
Answer: The place where an organism normally lives.
Q2Classify soil pH as a biotic or abiotic factor.Show answer
Answer: Abiotic
Q3In a food chain grass -> rabbit -> fox, identify the primary consumer.Show answer
Answer: Rabbit
Q4A pyramid of numbers for one oak tree covered in thousands of caterpillars would have an unusual shape. Name the type of pyramid that would give a more realistic true-pyramid shape for this food chain.Show answer
Answer: A pyramid of biomass
Q5Producers in a habitat store 300,000 kJ/m2/year of energy. Using the rule that only 10% of energy transfers between trophic levels, calculate the energy available to primary consumers.Show answer
Answer: 30,000 kJ/m2/year (300,000 x 0.1)
Q6A student marks and releases 25 snails, then recaptures a sample of 30 snails, of which 5 are marked. Estimate the total snail population.Show answer
Answer: 150 (25 x 30 / 5 = 150)
Exam-style questions
Written in the style of a KS3 Science exam paper, with a full mark scheme.
State what is meant by each of the following terms: population, community, ecosystem.
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A student estimates the percentage cover of daisies in a field with a total area of 600 m2. She uses a 1m x 1m quadrat, places it randomly 10 times, and finds a mean percentage cover of 24%. Explain why the quadrat positions should be chosen randomly, and calculate the estimated total area of the field covered by daisies.
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In a rocky shore ecosystem, starfish prey on mussels, and mussels compete with seaweed for space on the rocks. If starfish were removed from the ecosystem by disease, predict and explain what would happen to the mussel population and the seaweed population over time.
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Free printable worksheet
Want more practice on paper? Download the ecosystems and interdependence worksheet pack - 18 pages of exam-style questions with a full mark scheme. One email opens every download in this browser for 14 days - no account, no card. Print it for personal and classroom use.
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