Lymph's similarity to blood plasma

Steps:

• Lymph forms from interstitial fluid, derived from blood plasma leaking through capillary walls.
• Blood plasma includes water, electrolytes like sodium ions, and soluble proteins.
• White blood cells, especially lymphocytes, migrate into tissues and enter lymph vessels.
• Thus, lymph contains white blood cells, proteins, and sodium ions, but lacks red blood cells.

Why A is correct:

• Lymph is an ultrafiltrate of plasma, retaining ions (e.g., Na+), proteins (in lower amounts), and white blood cells per physiological definitions of lymphatic circulation.

Why the others are wrong:

• B: Proteins are present in lymph, albeit at reduced concentrations compared to plasma.
• C: White blood cells are present in lymph; sodium ions are also present as key electrolytes.
• D: White blood cells and sodium ions are both present in lymph.

Final answer: A