$(i)$ Why are the valves needed in the heart?
$(ii)$ Leakage of blood from vessels reduces the efficiency of the pumping system. How is the leakage prevented?

(N/A) $(i)$ Valves are needed in the heart to ensure that blood flows in only one direction and does not flow backward when the atria or ventricles contract.
$(ii)$ To prevent leakage,blood contains specialized cells called platelets. These platelets circulate throughout the body and plug any leakage by forming a clot at the site of an injury.