These seven original questions follow the four lessons in ecological evidence and population relationships. Try each one before opening its answer.
Questions
Q1. Eight random quadrats of 1 m² contain 3, 5, 4, 6, 2, 4, 5 and 3 plants. The field is 500 m². Estimate the population.
Answer
Total = 32, mean = 32 ÷ 8 = 4 per m². Estimate = 4 × 500 = 2 000 plants.
Q2. Why is the total count of 32 in Q1 not the population of the field?
Answer
It counts only the plants in the eight quadrats, which are a small sample of the field. The population needs the mean scaled up to the whole area.
Q3. 50 snails are marked and released. A later sample of 40 snails contains 8 marked. Estimate the population and state one assumption.
Answer
(50 × 40) ÷ 8 = 2 000 ÷ 8 = 250 snails. Assumption: marked snails mixed fully with the rest, or no snails entered or left between samples.
Q4. Producers store 10 000 kJ and the primary consumers gain 1 200 kJ. Find the percentage transferred.
Answer
1 200 ÷ 10 000 × 100 = 12%.
Q5. A student writes: “Decomposers return energy to the producers.” Correct the sentence.
Answer
“Decomposers return nutrients to the soil, but the energy is lost as heat and does not return. Producers obtain energy from sunlight.”
Q6. In the paddy web (rice, insects, rats, frogs, snakes, eagles), predict what happens to frogs if insects are removed, stating the link and an assumption.
Answer
Frogs decrease, because insects are their food. Assumption: frogs have no other food source in the web and all populations start stable.
Q7. Ants are counted in a field study and are found to be commoner where leaf litter is deeper. Write a safe conclusion and name another factor.
Answer
“Ants were commoner where leaf litter was deeper, which suggests an association, but does not show a cause.” Another factor: soil moisture or shade may differ and affect both.
If you got these wrong
Q1 to Q3 point to sampled count versus estimate. Q4 and Q5 need energy transfer.
Q6 links to comparing food-web changes, and Q7 to association or cause.
Use the timed practice builder to repeat questions and the mistake log to record errors. If you want a teacher to go through your working, see online one-to-one Biology tuition.