BIOLOGY 5090 · STRUCTURED PRACTICE
A quantitative ecological survey of a temperate grassland ecosystem measured the annual energy budget across several trophic levels. Incident solar energy hitting the grassland was 3 000 000 kJ m⁻² year⁻¹. The grass producers fixed 30 000 kJ m⁻² year⁻¹ into gross primary production, of which 15 000 kJ m⁻² year⁻¹ was lost as plant respiration. A population of herbivorous grasshoppers ingested 4500 kJ m⁻² year⁻¹ of grass biomass, assimilating 450 kJ m⁻² year⁻¹ into new insect tissue.
Define the term producer and state the form of energy that enters the grassland ecosystem from the Sun.
Calculate the percentage efficiency of energy transfer from the ingested grass to the new grasshopper biomass.
Explain two physiological reasons why 90% of the ingested energy is not converted into new grasshopper biomass.
Explain why food chains in this grassland rarely contain more than four trophic levels.
In a nearby woodland, a single mature oak tree supports 60 000 herbivorous caterpillars, which are preyed upon by 150 blue tits, which in turn are hunted by 2 sparrowhawks. Describe the difference in shape between a pyramid of numbers and a pyramid of biomass for this woodland food chain.
Total: 7 marks