These ten questions cover the whole ecology and energy flow module, from easy to harder. All data are invented for practice. Write a full answer for each one before opening the working, and record any slip in your mistake log.
Questions
Q1 (food chain). In a mangrove area, leaves fall into the water. Small crabs eat the leaves. Mudskippers eat the crabs, and a heron eats the mudskippers. Write the food chain with correct arrows.
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leaves → crab → mudskipper → heron. The arrow points from the food to the feeder, showing the direction energy passes.
Note: some courses treat fallen leaves as dead matter that feeds decomposers. Here the question says crabs eat the leaves, so you write it as a chain.
Q2 (trophic levels). In the chain grass → grasshopper → lizard → eagle, name the producer, the secondary consumer and the trophic level of the eagle.
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Producer: grass. Secondary consumer: lizard, because it eats the primary consumer (the grasshopper). The eagle is at trophic level 4.
Q3 (percentage). A field has 15 000 kJ of energy in its plants. The caterpillars eating them hold 2 400 kJ. Calculate the percentage of energy passed to the caterpillars.
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2 400 ÷ 15 000 × 100 = 16%. Check: 0.16 × 15 000 = 2 400.
Q4 (percentage, next step). Small birds eating those caterpillars hold 288 kJ. Calculate the percentage passed on from caterpillars to birds, and the energy not passed on from the plants to the caterpillars.
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Birds: 288 ÷ 2 400 × 100 = 12%. Check: 0.12 × 2 400 = 288.
Not passed on from plants: 15 000 − 2 400 = 12 600 kJ.
Q5 (explain). Give two reasons why the caterpillars hold much less energy than the plants.
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Any two of: not all the plant is eaten (roots, stems or some leaves may be left); some energy in the plants is released by the plants’ own respiration; some of what is eaten is not digested and leaves as faeces; much energy the caterpillars take in is released as heat by their respiration. Do not write “used up”.
Q6 (food web change). A field has this web: grass → rabbit, grass → vole, rabbit → fox, vole → fox, vole → owl. A disease removes most of the rabbits. Suggest what may happen to the voles and the owls, and explain.
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Voles: fewer rabbits means the fox may eat more voles, so vole numbers may decrease. There may also be less grass competition, which could help voles a little, so the net effect is uncertain.
Owls: if vole numbers fall, the owls’ food supply falls, so owl numbers may decrease. If owls eat other prey not shown, the effect could be small.
The web supports likely effects, not one certain outcome.
Q7 (wording). Improve this answer: “If all the foxes are removed, the voles will multiply until the grass is gone.”
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“If the foxes are removed, vole numbers may increase because fewer are eaten, although owls still eat voles and food supply could limit the increase. More voles could eat more grass, so grass may decrease.” It replaces “will” and “gone” with cautious wording and adds reasons.
Q8 (quadrats). Six 0.25 m² quadrats are placed at random on a lawn of area 60 m². The numbers of daisies counted are 6, 4, 5, 3, 7, 5. Estimate the number of daisies on the lawn.
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Total = 6 + 4 + 5 + 3 + 7 + 5 = 30. Mean = 30 ÷ 6 = 5 per quadrat.
Density = 5 ÷ 0.25 = 20 per m². Estimate = 20 × 60 = 1 200 daisies.
Check: area sampled = 6 × 0.25 = 1.5 m², and 30 ÷ 1.5 = 20 per m². Matches.
Q9 (mark-recapture). 60 snails were marked and released. A second sample had 45 snails, and 9 were marked. Estimate the population and state two assumptions.
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60 × 45 ÷ 9 = 2 700 ÷ 9 = 300 snails. Check: 9 of 45 is one fifth, and 60 is one fifth of 300.
Assumptions (any two): marking does not harm the snails or make them easier to catch; marked snails mix fully with the rest; no snails enter or leave the area; the population does not change much between samples.
Q10 (biomass). In a woodland: 1 tree of dry mass 200 kg; 10 000 beetles of mean dry mass 0.1 g; 15 lizards of mean dry mass 40 g. Find the total biomass of each level and describe both pyramids.
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Tree: 200 kg. Beetles: 10 000 × 0.1 = 1 000 g = 1 kg. Lizards: 15 × 40 = 600 g = 0.6 kg.
Numbers: 1, 10 000, 15, so the middle bar is widest and it is not a pyramid. Biomass: 200, 1, 0.6 kg narrows upwards, so it is a pyramid. The count ignores the size of each organism.
If you got these wrong
- Reversed arrows or wrong trophic level (Q1, Q2): revisit constructing a food chain with the correct arrow meaning.
- Wrong percentage or vague reasons (Q3 to Q5): revisit explaining energy losses between trophic levels. Remember to divide by the level the energy came from.
- Over-confident predictions (Q6, Q7): revisit interpreting a food web change and check your picture with the food-web and energy-flow explorer.
- Scaling mistakes (Q8, Q9): revisit calculating a sampling estimate with stated assumptions. Convert to per m² first, then multiply by the area.
- Counts versus mass (Q10): revisit comparing biomass and organism counts.
Some students see the same kind of error three times in a set of ten. That is a useful pattern, and online one-to-one Biology tuition works on exactly that kind of repeat slip. For the wider picture, return to the Biology learning guide.