Energy transfer and nutrient recyclingEdexcel A-Level Biology B: Mind map

Exam questions on Energy transfer and nutrient recycling

1. In a grassland, the gross primary productivity (GPP) of the plants is 20 000 kJ m⁻² year⁻¹. The plants lose 8 000 kJ m⁻² year⁻¹ as heat in respiration.
   Calculate the NPP of the grassland as a percentage of its GPP.2 marks
2. The energy stored in the biomass at three trophic levels of a lake food chain was measured over one year. Producers: 31 200 kJ m⁻² year⁻¹. Primary consumers: 3 380 kJ m⁻² year⁻¹. Secondary consumers: 405 kJ m⁻² year⁻¹.
   Calculate the efficiency of energy transfer from the primary consumers to the secondary consumers. Give your answer to one decimal place.2 marks
3. A farmer rears beef cattle in two ways. Group X graze freely outdoors on pasture. Group Y are kept in heated barns with little room to move and are fed on concentrated feed. After 12 months, the cattle in group Y have gained more body mass per unit of food energy than those in group X.
   Suggest three reasons why the cattle in group Y convert more of their food energy into body mass than those in group X.3 marks