Few candidates attempted this question. In 4 a(i) and (ii), majority of the candidates were able to define inorganic fertilizer and list methods of fertilizer application.
However, in 4 b(i-iv), majority of the candidates could not describe an experiment to show the presence of living micro-organism in a sample of fresh garden soil. In 4(c), many candidates were able to state ways in which the carbon cycle is important in agriculture.
The expected answers include:
Description of experiment to show the presence of living micro-organisms in a sample of fresh garden soil:
Apparatus and materials
- Two 25cm3 conical flasks
- Rubber corks
- Lime water
- Garden soil(fresh)
- Heated garden soil
- Muslin bag
- Source of heat (Heater).
- Put a handful of fresh garden soil in muslin bag and suspend it with the string in a flask labeled A, containing lime water and cork it.
- In another muslin bag, put another sample of garden soil which has been strongly heated to kill any living organisms in it; and suspend it with the string in a flask labeled B, containing lime water and cork it.
- Leave the set-up for about 4 hours.
The lime water in flask labeled A containing the fresh soil will turn milky, whilst that in flask B containing the heated soil B will remain clear.
When carbon dioxide dissolves in lime water, it turns milky-Carbon dioxide which turned the lime water milky in the flask A containing fresh soil is from respiration by living organisms present in the fresh soil.
There is no respiration to produce any carbon dioxide in the soil in flask B because the organisms are dead, as a result of the heating. This is why the lime water in flask B remains clear.