Which amino acid is present only in bacteria and cyanobacteria?

The correct option is D Diaminopimellic acid
The cell wall of bacteria and cyanobacteria is made up of Peptidoglycan or murein. It is a polymer that is made up of sugars and amino acids. Diaminopimelic acid and muramic acid amino acids are present in the wall of bacteria and cyanobacteria. The sugar component is made up of alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM). Muramic acid is then attached to the amino acid chain of L-alanine, D-glutamic acid, diaminopimelic acid (DAP) and D-alanine.

Thus, the correct answer is 'Diaminopimellic acid.'