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Date May 2021 Marks available 1 Reference code 21M.1.SL.TZ2.18
Level Standard level Paper Paper 1 Time zone Time zone 2
Command term Question number 18 Adapted from N/A

Question

The diagram shows the flow of energy through an ecosystem in kJ m–2 y–1.

[Source: “Energy flow: Figure 3,” (https://cnx.org/contents/24nI-KJ8@24.18:fbNheNoN@8/Energy-Flow) by OpenStax College, Biology CC BY 4.0 (https://creativecommons.org/licenses/by/4.0/).]

What percentage of the energy passed from primary producers to primary consumers is lost to cellular respiration by tertiary consumers?

A. 0.001%

B. 0.08%

C. 0.2%

D. 0.4%

Markscheme

D

Examiners report

The candidates found this question difficult, possibly because the arrow coming from the primary producers shows 40 000 kJ m−2 y−1 leaving but only half of that is taken up by primary consumers, the remainder being lost to saprotrophs and detritivores. Some G2 forms suggested that the calculation was too difficult without the aid of a calculator but if the candidates had chosen the correct values from the diagram the calculation would have been straightforward (80 ×10020 000=0.4 %).

Syllabus sections

Core » Topic 4: Ecology » 4.2 Energy flow
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