(a) Explain the following terms: (i) putrefaction (ii) nitrogen fixation (iii) nitrification (iv) denitrification (b) State three differences between nitrog...

(a) Explanation of terms

• (i) Putrefaction: the decomposition (breakdown) of nitrogenous organic matter such as dead plants, animals and their wastes by putrefying bacteria and fungi, releasing ammonia and ammonium compounds.
• (ii) Nitrogen fixation: the conversion of free atmospheric nitrogen gas into nitrogen compounds (ammonia/nitrates) that plants can use, carried out by nitrogen-fixing bacteria (e.g. Rhizobium, Azotobacter) and by lightning.
• (iii) Nitrification: the conversion of ammonia/ammonium compounds first to nitrites (by Nitrosomonas) and then to nitrates (by Nitrobacter) by nitrifying bacteria in the soil.
• (iv) Denitrification: the conversion of soil nitrates back into free nitrogen gas, which escapes into the atmosphere, carried out by denitrifying bacteria (e.g. Pseudomonas).

(b) Three differences between nitrogen fixation and denitrification

(c) How nitrogen from urine gets to the roots of plants

Urine contains urea, a nitrogenous waste. In the soil, bacteria break down the urea into ammonia/ammonium compounds (ammonification/putrefaction). Nitrifying bacteria then convert the ammonium compounds first into nitrites and then into nitrates (nitrification). The nitrates dissolve in the soil water and are absorbed by the roots of the plant, which use them to make proteins. In this way the nitrogen of urine reaches the roots.