BLOOD ➖The blood is responsible to transport food, oxygen, and waste materials in human bodies. ➖Blood usually consists of a fluid medium known as plasma where the cells remain suspended. ➖Plasma is responsible to transport food, carbon dioxide, and nitrogenous wastes in dissolved form. ➖However, oxygen is carried by the red blood cells. ➖Many other substances such as salts, are also transported by the blood. A HUMAN HEART ➖The heart is one of the most significant muscular organs of a human body. ➖As both the oxygen and the carbon dioxide get transported by the blood; so, to avoid the oxygen-rich blood from mixing with the blood containing carbon dioxide, the heart has different chambers. ➖Oxygen-rich blood from the lungs comes to the thin-walled upper chamber of the heart on the left, i.e. the left atrium (see the image given above). ➖When it is collecting the blood, the left atrium relaxes; however, while the next chamber, i.e. the left ventricle expands, then it (l...