Question

what is the main role of the hearts valves?
a. to increase blood pressure
b. to prevent the backflow of blood

what component of blood is responsible for blood clotting?
a. red blood cells
b. platelets

which blood vessels are responsible for the exchange of nutrients and gases between blood and tissues?
arteries
b. capillaries

what is the primary function of white blood cells in the circulatory system?
a. to form blood clots
b. to defend the body against infections

Explanation:

First Question (Main role of heart’s valves)

Heart valves prevent backflow of blood (ensure one - way flow). Option a (increase blood pressure) is incorrect as valves don't increase pressure.

Red blood cells carry oxygen. Platelets (thrombocytes) are responsible for blood clotting.

Arteries carry blood away from heart. Capillaries have thin walls, allowing exchange of nutrients, gases between blood and tissues.

Answer:

b. To prevent the backflow of blood

Second Question (Blood component for clotting)