Decomposition and carbon recyclingEdexcel International A Level Biology: Mind map

Exam questions on Decomposition and carbon recycling

1. A gardener makes a compost heap from grass cuttings, vegetable peelings and fallen leaves. After eight weeks the material has become a dark, crumbly substance, and the heap has been noticeably warm throughout.
   Explain how fungi in the heap digest the dead plant material.2 marks
2. A student buries identical masses of dry leaves in mesh bags in soil kept equally moist at four different temperatures. After four weeks she measures the percentage loss in mass of the leaves: 4% at 5 degrees Celsius, 13% at 15 degrees Celsius, 32% at 25 degrees Celsius and 21% at 35 degrees Celsius.
   Explain why the leaves lost mass during the investigation.2 marks
3. In a woodland, carbon dioxide from the atmosphere is incorporated into the leaves of trees. When the leaves fall, they are broken down in the soil by bacteria and fungi. In a waterlogged peat bog nearby, dead plant material has built up over thousands of years to form deep layers of peat.
   Describe how carbon in atmospheric carbon dioxide is incorporated into a leaf and later returned to the atmosphere after the leaf has fallen.3 marks