CBSE Class 10 Science 2020 · Paper 31/3/1 · Question 27

(a) Oxygen-rich blood from the lungs $\to$ pulmonary veins $\to$ left atrium, which relaxes and collects the blood $\to$ the left atrium contracts $\to$ the blood passes into the left ventricle, which expands and collects it $\to$ the left ventricle contracts $\to$ the blood is pumped into the aorta $\to$ the aorta and its branches carry it to the various organs of the body. (b) A leak causes loss of blood and a fall in blood pressure, which reduces the efficiency of the pumping system. Platelets in the blood plug such leaks by helping the blood to clot at the point of injury.