Correct distribution of antigens in body fluids

Steps:

• Identify the substance in each option: A (antigen), B (glucose), C (lymphocyte), D (neutrophil).
• Recall locations: blood carries substances systemically; lymph transports immune cells; tissue fluid bathes cells in tissues.
• Match presences: antigens enter via infection sites, appearing in blood and tissue fluid but filtered out of lymph.
• Verify option A matches: ✓ blood, x lymph, ✓ tissue fluid.

Why A is correct:

• Antigens are foreign molecules that provoke immune responses, present in blood (circulation) and tissue fluid (infection sites) but absent in lymph, which mainly carries lymphocytes.

Why the others are wrong:

• B: Glucose, a simple sugar, diffuses into all three fluids for cellular energy supply.
• C: Lymphocytes, key immune cells, circulate in blood and lymph nodes (thus lymph) and migrate to tissue fluid during responses.
• D: Neutrophils, phagocytic white blood cells, reside in blood and enter tissue fluid at infection sites but rarely in lymph.

Final answer: A