The nitrogen cycle and the phosphorus cycleAQA A-Level Biology: Mind map

Exam questions on The nitrogen cycle and the phosphorus cycle

1. In a woodland, fungi and bacteria in the soil feed on dead leaves, dead animals and faeces. Over time the nutrients in this dead material are released and become available again to the trees.
   Explain why the activity of fungi and bacteria in the woodland soil is essential for the trees to grow.2 marks
2. A farmer notices that wheat grows poorly and has yellow leaves in a part of a field where the soil is badly drained and waterlogged for much of the year. The farmer has applied ammonium fertiliser to the whole field, but the wheat in the rest of the field grows well.
   Explain why the wheat in the waterlogged part of the field shows signs of nitrogen deficiency even though ammonium fertiliser was added.2 marks
3. Pine seedlings were grown for six months in sterilised soil with a very low concentration of phosphate ions. Some seedlings were inoculated with a mycorrhizal fungus and the others were not. The mean dry mass of the inoculated seedlings was 2.4 g and the mean dry mass of the uninoculated seedlings was 0.9 g.
   Calculate the percentage increase in mean dry mass of the inoculated seedlings compared with the uninoculated seedlings. Give your answer to the nearest whole number.3 marks