Ecosystems and energy transfer

Sample questions

Original practice questions written in the style of the exam.

1. Question 12 marks

   In a seagrass ecosystem, the energy in primary consumers is $12\,000\,\text{kJ m}^{-2}\,\text{yr}^{-1}$ and the energy in secondary consumers is $1\,080\,\text{kJ m}^{-2}\,\text{yr}^{-1}$.

   Calculate the percentage efficiency of energy transfer from primary to secondary consumers.

   Mark scheme

   • Efficiency $= \dfrac{1\,080}{12\,000} \times 100$ (1)
   • $= 9\%$ (1)
2. Question 24 marks

   Explain why only a small proportion of the energy in plants is transferred to the primary consumers that feed on them.

   Mark scheme

   • Not all parts of the plant are eaten (e.g. roots, woody tissue) (1)
   • Some parts are indigestible (e.g. cellulose, lignin) and are lost in faeces (1)
   • Energy is lost as heat in respiration / used for movement and other life processes (1)
   • Energy is lost in excretory products such as urine (1)