What is blood? Write down four functions of blood.

A fluid connective tissue of red colour, alkaline, salty or colloidal in nature which is used for circulation of substances in the body is called blood.
Functions of blood -

1. Blood absorbs the digested part of the food and transports it to all cells of the body.
2. It transports the oxygen from lungs to the cells.
3. It transports the carbon dioxide produced in the cells due to respiration to the lungs.
4. It transports excreta such as urea, uric acid, etc. to the kidney the excretory organ.
5. It protects from diseases in the following ways - (i) Neutrophils and monocytes etc. engulf the harmful bacteria and other disease-causing organisms. (ii)Blood helps in excretion of dust particles, dead and damaged blood corpuscles in the form of pus. (iii) It produces antibodies with the help of lymphocytes to neutralise the action of toxins produced by pathogens.
6. blood forms a clot at the site of injury and thus prevents the further loss of blood. Blood helps in rapid healing.
7. It regulates the body temperature.
8. It transports the hormones secreted by endocrine ductless glands.
9. It maintains the water balance of the body.
10. Transports the metabolic intermediates.
11. Maintains the pH value of the body tissues.
12. Transports the toxic substances to the liver for making them less toxic.