Productivity and energy transferEdexcel International A Level Biology: Mind map

Exam questions on Productivity and energy transfer

1. In a grassland ecosystem the gross primary productivity (GPP) of the plants is 14 500 kJ m⁻² year⁻¹. The plants lose 6 000 kJ m⁻² year⁻¹ as a result of respiration (R).
   Calculate the percentage of the GPP that is lost in respiration. Show your working.2 marks
2. In a food chain in a freshwater ecosystem, the net primary productivity of the producers is 12 000 kJ m⁻² year⁻¹. The energy stored in the biomass of the primary consumers (zooplankton) is 1 080 kJ m⁻² year⁻¹ and the energy stored in the biomass of the secondary consumers (small fish) is 130 kJ m⁻² year⁻¹.
   The efficiency of transfer from the primary to the secondary consumers is 12.0%, which is greater than the efficiency from the producers to the primary consumers. Suggest why.2 marks
3. Over one year a field of maize receives 30 000 kJ m⁻² of light energy. The maize fixes 600 kJ m⁻² in gross primary productivity and loses 200 kJ m⁻² in respiration.
   Calculate the net primary productivity of the maize and the percentage of the light energy that is converted to net primary productivity. Show your working.3 marks