About how much blood is in the circulatory system of an average person?
A. 1 litre
B. 2 litres
C. 5 litres
D. 10 litres

Hint: Blood is the main body fluid present in both humans and animals. It delivers substances such as nutrients, oxygen, hormones, etc. to cells and also transports metabolic pathway waste products away from cells eliminating them from the body. Blood is composed of the blood cells present in the blood plasma in vertebrates.

Complete answer: The blood consists of mainly red blood cells or erythrocytes, white blood cells or leukocytes, and platelets also called thrombocytes. Red blood cells are the most abundant cells in vertebrates containing the haemoglobin, iron-containing protein, that facilitates oxygen transport by the reversible mechanism. 7 percent of the body weight is accounted for by the blood. The average adult has a volume (5 litres) containing plasma and several cells like thrombocytes, erythrocytes, and leukocytes. Plasma circulates dissolved nutrients, such as glucose, amino acids, and fatty acids, and removes waste products, such as carbon dioxide, urea, and lactic acid. The blood PH is between 7.35 to 7.45 which is slightly basic. Blood is circulated in the body through blood vessels by the pumping action of the heart. Blood is pumped from arteries of the strong left ventricle of the heart to peripheral tissues and returns to the right atrium through veins.
Hence, the correct answer is option C.

Note: The deoxygenated enters the right ventricle and is pumped through the pulmonary artery to the lungs and returns to the left atrium through pulmonary veins. Blood is circulated again entering the left ventricle. The heart is a muscular organ that consists of four chambers in humans divided by a septum.