Which of the following is a primary function of blood?

• A. Digesting nutrients
• B. Transporting oxygen
• C. Producing hormones
• D. Regulating body temperature

Answer: (B)

Blood serves as the body's transport system, delivering what the cells need and carrying away wastes. A key part of this is moving oxygen from the lungs to every tissue so cells can produce energy through respiration. Red blood cells carry oxygen bound to hemoglobin, and the bloodstream returns carbon dioxide to the lungs to be expelled. Among the options, transporting oxygen directly reflects this essential transport role.

Digesting nutrients happens in the digestive system, not by blood itself. Hormones are produced by endocrine glands, with blood mainly acting to transport them where needed rather than making them. Regulating body temperature is helped by blood flow distributing heat, but that’s a secondary effect of circulation rather than the primary function.