1
Triple only
[1 mark]Food chains rarely have more than five trophic levels because
- there is too little light for plants
- too little energy is left to support more trophic levels
- predators eat too many organisms
- plants cannot grow near large animals
Show mark scheme
Answer: B too little energy is left to support more trophic levels (1)
2
Triple only
[3 marks]In a field, the biomass of the grass is much greater than the biomass of the cows that eat it. Explain why.
Show mark scheme
- some of the grass is not eaten / some is not digested and is lost in faeces (1)
- energy is released by respiration and transferred to the surroundings as heat (1)
- energy is used for movement / keeping warm / lost in urine (1)
- so less energy / biomass is available at the next trophic level to support cows (1)
- Max 3
3
Triple only
[2 marks]A field of grass contains 12 500 kJ of energy in its biomass. Rabbits eating the grass gain 1 500 kJ. Calculate the percentage efficiency of the energy transfer from grass to rabbits.
Show mark scheme
- 1 500 ÷ 12 500 × 100 (1)
- = 12 % (1) award 2 marks for a correct answer with no working
4
Triple only
[2 marks]A caterpillar eats 50 g of leaf (dry mass). Its own dry mass increases by 8 g. Calculate the percentage of the dry mass of leaf eaten that becomes caterpillar biomass.
Show mark scheme
- 8 ÷ 50 × 100 (1)
- = 16 % (1) award 2 marks for a correct answer with no working