QUESTION 46 (7 marks)
The diagram shows an annual energy budget. All values are in . The producer input is gross primary productivity. Assume the grazer energy budget is complete.
a) Calculate net primary productivity. [1 marks]
b) Calculate energy stored in new grazer biomass. [2 marks]
c) Calculate the efficiency of transfer from producer net production to new grazer biomass. [2 marks]
d) Explain why the energy available to the next trophic level is lower than grazer food intake. [2 marks]
Practice marking scheme
Answer
a) 15000 kJ m⁻² year⁻¹. b) 3500 kJ m⁻² year⁻¹. c) 23.3%. d) Energy is lost in unassimilated material and respiration/heat.
Working
. Grazer production equals intake minus egested energy and respiration: . The requested transfer efficiency is . Energy in unassimilated material is not incorporated into grazer biomass, while respiration transfers energy to the surroundings as heat.
Marking criteria
- Calculates NPP as 15000. [1 mark]
- Subtracts both egestion and respiration from grazer intake. [1 mark]
- Calculates grazer production as 3500. [1 mark]
- Uses producer NPP as the efficiency denominator. [1 mark]
- Calculates 23.3%. [1 mark]
- Explains loss through unassimilated/egested material. [1 mark]
- Explains respiratory energy loss as heat. [1 mark]
Practice question aligned to the current QCAA syllabus; review the worked solution and marking criteria.
View the QCAA syllabusCompare your working with the guide above.