These eight original questions cover ecosystems: energy flow, trophic levels and sampling data. Try each before opening the answer.
Questions
Q1. Producers store 15 000 kJ and primary consumers gain 1 800 kJ. Find the percentage transferred.
Answer
1 800 ÷ 15 000 × 100 = 12%.
Q2. Secondary consumers gain 150 kJ from primary consumers that hold 1 800 kJ. Find the percentage and state the trend compared with Q1.
Answer
150 ÷ 1 800 × 100 ≈ 8.3%. Both transfers are below 20%, so energy falls at each level, and this step is slightly lower than the one in Q1.
Q3. Give two reasons why energy is lost between trophic levels.
Answer
Heat released in respiration, and parts of the organism that are not eaten or are lost as waste. Both stop the energy from reaching the next level.
Q4. Explain why a food chain rarely has more than five trophic levels.
Answer
Energy is lost at each level, so very little remains at the top. There is not enough energy to support a further population of consumers.
Q5. 4 quadrats of 0.5 m² contain 6, 8, 7 and 7 plants. Find the density.
Answer
Total = 28, area = 4 × 0.5 = 2 m². Density = 28 ÷ 2 = 14 per m².
Q6. Site P: 5 quadrats of 1 m² with 40 plants. Site Q: 8 quadrats of 1 m² with 56 plants. Which has the higher density?
Answer
P: 40 ÷ 5 = 8 per m². Q: 56 ÷ 8 = 7 per m². Site P is denser, although Q has the larger total.
Q7. A shaded zone has a mean of 3 plants per quadrat and an open zone has 7. Suggest a reason for the difference.
Answer
The open zone may receive more light, so plants photosynthesise more and grow better. “May” is used because the survey does not test the cause.
Q8. A student says a pyramid of energy can be inverted. Is this correct?
Answer
No. Energy is lost at each level, so each level holds less energy than the one below. A pyramid of numbers or biomass can look unusual, but a pyramid of energy cannot be inverted.
If you got these wrong
Q1 to Q4 point to explaining energy flow. Q5 to Q7 use interpreting population sampling data.
For deeper reasoning about estimates, see ecological evidence and population relationships. Use the timed practice builder to repeat questions and the mistake log to record slips.
If you want a teacher to go through your working, see online one-to-one Biology tuition.