QUESTION 50 (5 marks)
A lake has a standing biomass of 18 kg of phytoplankton and 54 kg of zooplankton at one sampling time. Over the month, new biomass production is 900 kg for phytoplankton and 90 kg for zooplankton.
a) Calculate biomass-transfer efficiency using monthly production. [2 marks]
b) Explain how the inverted standing-biomass pyramid can coexist with lower production at the higher trophic level. [3 marks]
Practice marking scheme
Answer
a) 10%. b) Phytoplankton can have rapid turnover: low standing biomass but high production; zooplankton can accumulate biomass over a longer lifespan.
Working
Transfer efficiency is . Standing biomass is an instantaneous stock; productivity measures production over time. Rapid phytoplankton growth and consumption can keep their standing stock low despite high monthly production. Longer-lived zooplankton may have a larger standing stock without producing more biomass per month.
Marking criteria
- Uses production values rather than standing biomass. [1 mark]
- Calculates 10%. [1 mark]
- Distinguishes standing stock from production over time. [1 mark]
- Explains rapid producer turnover or rapid consumption. [1 mark]
- Explains that consumers can accumulate standing biomass over longer periods. [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.