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Composition of Blood

       In human body, various substances such as oxygen, digested food, hormones and enzymes are transported from one part of the body to other parts through blood and lymph. Blood is red in colour due to the presence of red coloured pigment called haemoglobin in it. basically, blood is a connective tissue. In a healthy person about 5.5 litre of blood is present in the body.

The main components of blood are :

  1. Red Blood Corpuscles or Red Blood Cells (RBC)
  2. White Blood Corpuscles or White Blood Cells (WBC)
  3. Platelets, and
  4. plasma

let’s now discuss the various components of blood more detail.

Red Blood Cells

Red Blood Cells       Red blood cells are circular, non-nucleated cells which are red in colour due to the presence of a red coloured pigment called haemoglobin in them. The function of red blood cells is to transport oxygen from lungs to different tissues of the body and carbon dioxide from tissues to lungs. The life span of red blood cells is about 120 days.

White Blood Cells

White Blood Cell       White blood cells are spherical or irregular in shape, nucleated and larger than red blood cells. There number is much less than red blood cells. The main job of white blood cells is to eat up bacteria and fight infection. White blood cells also produce antibodies which help us in fighting infection and protect us from diseases. Thus, white blood cells provide immunity to out body. Due to these reasons, white blood cells are also called soldiers of the body. The average life span of white blood cells is 3 – 4 days.

Blood PlateletsPlatelets

       Platelets are tiny fragments of cells, which help the blood to clot when you cut yourself. The average life span of platelets is 7 days.


       Blood is made up of a pale yellow liquid called plasma. It contains red blood cells, white blood cells and blood platelets. Blood plasma also contains dissolved particles of food (like proteins, glucose, amino acids, fatty acids and minerals), waste materials (like carbon dioxide and urea) and hormones.

Functions of Blood

       Following are the functions of blood in our body:

  1. Oxygen is transported from the lungs to all the parts of body through blood.

  2. Blood also transports carbon dioxide from the tissues to lungs.

  3. Blood helps us in fighting infection by eating up bacteria and protects us from diseases.

  4. Blood transports the food absorbed in the intestine to all the parts of the body.

  5. Blood also transports various types of hormones and enzymes from one part of the body to other parts.

  6. It plays a role in regulating the temperature of body.

  7. Blood also helps in excretion of waste materials such as urea out of the body.

  8. Blood solidifies (clots) at the site of an injury or cut and thus prevents its loss from the body.

Test Your Understanding and Answer These Questions:

  1. What is blood plasma?

  2. What are blood platelets?

  3. List the components of blood.

  4. What makes red blood cells red?

  5. What is the life span of blood platelets?

  6. What are different functions of blood?

  7. What is blood? Describe its composition.

  8. What is the life span of white blood cells?

  9. Give the structure and function of red blood cells.

  10. How much blood is present in a healthy human being?

  11. What are the medium of transportation in human body?

  12. Which component of blood kills bacteria in human body?

  13. Why white blood corpuscles are are called ‘soldiers of the body’?

  14. Give differences between red blood cells and white blood cells.

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