In forensic biology, the significance of PSA is that

• A. A positive PSA test can unequivocally identify the presence of semen.
• B. PSA indicates sperm motility.
• C. PSA confirms blood type.
• D. PSA detects saliva.

Answer: (A)

PSA stands for prostate-specific antigen, a protein produced in seminal plasma. In forensic biology, testing for PSA is used to indicate the presence of seminal fluid in a sample. Because PSA is abundant in semen and relatively specific to it, a positive PSA result is treated as strong evidence that semen was present. This is why it’s the best answer among the options: it directly points to semen presence, whereas the other statements refer to sperm motility, blood type, or saliva, which PSA testing does not address. In practice, PSA testing serves as a screening tool for semen, often followed by additional tests (like microscopy for sperm or DNA analysis) if needed.