In nutrient-rich environments (like your mouth), bacteria can use the provided amino acids to synthesize their proteins. However, should the environmental conditions change and become nutrient-poor, bacteria would need to synthesize their amino acids. They can do this using __________.

A. citric acid cycle intermediates
B. glucose
C. ATP
D. glyceraldehyde-3-phosphate

The citric acid cycle is the cyclic chain of reactions taking place as a phase of the cellular respiration as it gets halted in the absence of oxygen. The citric acid cycle converts the obtained acetyl-CoA to a usable form of energy in the form of ATP, NADH and FADH₂.

The citric acid cycle forms intermediates which are utilised by the organisms to synthesise the various biomolecules like amino acids, purines and pyrimidines.

The intermediates like alpha-ketoglutarate forms arginine, proline and glutamine whereas oxaloacetate forms asparagine and aspartate. If bacteria do not receive the amino acids then they will synthesise the amino acids using intermediates of the citric acid cycle.

Thus, option-A is the correct answer.