A common component of blood and lymph is

Analyze the question: We need something found in both blood and lymph.

Explain the concept:

• Blood consists of plasma, red blood cells (erythrocytes), white blood cells (leucocytes) and platelets.
• Lymph is a fluid formed from tissue fluid that drains into lymphatic vessels. It is essentially plasma-like fluid with white blood cells (lymphocytes). It normally has no red blood cells and few or no platelets.

Check each option:

• A. Fats: Fats (lipids) are carried in lymph, especially from the lacteals in the small intestine, and traces are also in blood. However, fats are not a structural "component" of both in the way cells are. This is not the best choice.
• B. Plasma: Plasma is the liquid part of blood. Lymph is derived from plasma, but it is called lymph, not plasma. It is similar to plasma but not identical, so plasma is not usually taken as a component of lymph.
• C. Red blood cell: Present in blood, absent from lymph. Wrong.
• D. White blood cell: Present in blood (all types) and in lymph (lymphocytes). This is the component common to both.

Answer: D.

Tip: Remember "Lymph = blood minus red cells (and most proteins)". Whatever is in lymph that is also in blood must be a white cell. In JAMB, if a question asks for what is common to blood and lymph, think of white blood cells (lymphocytes).