This question was poorly attempted by the candidates. In question 3(a), many candidates could state the ways by which nitrogen is added to the soil in the Nitrogen cycle. In question 3(b), some of the candidates could list the ways by which nitrogen is lost from the soil.
However, in questions 3(c) & (d), majority of the candidates could neither state the importance of the Nitrogen cycle nor explain the processes leading to the formation of nitrate from organic matter in the Nitrogen cycle.
The expected answers include:
Ways by which soil Nitrogen is lost from the soil:
- bush burning;
- leaching;
- crop removal;
- erosion of top soil;
- denitrification;
- volatilization;
- oxidation reaction;
- reduction reaction.
The importance of the Nitrogen cycle
- It is the nature’s way of regulating the amount of nitrogen in the soil and air.
Explanation of the processes involved in the formation of nitrate from organic matter in the
Nitrogen cycle:
- Putrefaction
- Amminization
- Ammonification/mineralization
- Nitrification.
Putrefaction: Decay of plant and animal remains into simpler nitrogenous compounds by micro-organisms.
Aminization: Products from putrefactions reaction converted to simple amino compounds and amines.
Ammonification: Conversion of amino compounds and amines into ammonium (NH4+) compounds.
Nitrification: Oxidation of ammonium compounds into nitrites and nitrates.
