Question

Countercurrent exchange mechanism is used by

I. Gills
II. Kidneys
III. Intestines
IV. Lungs

• A. I and III only
• B. II and IV only
• C. I, II and III
• D. I, II and IV
• E. I, II, III and IV

Answer 1

The correct option is D I, II and IV

Countercurrent exchange system refers to the mechanism that ensures maximum exchange between two fluids. The two fluids flow in opposite directions and have a concentration gradient between them to allow the exchange of substances or gasses. In biological systems, countercurrent exchange mechanism is used by fish in their gills to transfer oxygen from the surrounding water into their blood. Further, this mechanism is also used by the birds in the blood vessels of their legs to maintain the body heat. Mammalian kidneys use countercurrent exchange mechanism to remove water from urine so the body can retain water to move the nitrogenous waste products. Thus, the correct answer is option D.