A) The main function of nitrifying bacteria is to convert ammonia (NH3) or ammonium ions (NH4^+) into nitrites (NO2^-) and then into nitrates (NO3^-) in the s

Here are the answers to your questions:

a) The main function of nitrifying bacteria is to convert ammonia ($\text{NH}_3$) or ammonium ions ($\text{NH}_4^+$) into nitrites ($\text{NO}_2^-$) and then into nitrates ($\text{NO}_3^-$) in the soil. This process is called nitrification.

b) The main function of nitrogen-fixing bacteria is to convert atmospheric nitrogen gas ($\text{N}_2$) into ammonia ($\text{NH}_3$), which can then be used by plants. This process is called nitrogen fixation.

c) Animals obtain their protein by consuming other organisms, such as plants or other animals, that contain protein. Their digestive systems then break down these proteins into amino acids, which are reassembled to form the animal's own proteins.