Body Fluids and Circulation — BIOLOGY STD 11 Science — Question

1. Erythrocytes: They are also known as Red Blood Cells (RBC). They are the most abundant of all the cells in blood. A healthy adult man has, on an average, 5 millions to 5.5 millions of RBCs mm of blood. RBCs are formed in the red bone marrow in the adults. RBCs are devoid of nucleus in most of the mammals and are biconcave in shape. They have a red coloured, iron containing complex protein called haemoglobin, hence the colour and name of these cells. A healthy individual has 12-16gms of haemoglobin in every 100ml of blood. These molecules play a significant role in transport of respiratory gases. RBCs have an average life span of 120 days after which they are destroyed in the spleen. Hence, spleen is also known as the graveyard of RBCS.

2. Leucocytes: They are also known as White Blood Cells (WBC) as they are colourless due to the lack of haemoglobin. They are nucleated and are relatively lesser in number which averages 6000-8000mm of blood. Leucocytes are generally short lived There are two main categories of WBCs:

1. Granulocytes, e.g., neutrophils, eosinophils and basophils
2. Agranulocytes. e.g., Lymphocytes and monocytes.

• Neutrophils are the most abundant cells (60-65 percent of the total WBCs and basophils are the least 10.5-1 percent) among them. Neutrophils and monocytes (6-8 percent) are phagocytic cells which destroy foreign organisms entering the body.
• Basophils secrete histamine, serotonin, heparin, etc., and are involved in inflammatory reactions.
• Eosinophils (2-3 percent) resist infections and are also associated with allergic reactions.
• Lymphocytes (20-25 percent) are of two major types - 'B' and T forms. Both B and T lymphocytes are responsible for immune responses of the body.

3. Structure of Heart: The heart is a muscular organ. It consists four chambers which are as follows:

• Right Auricle.
• Left Auricle.
• Right Ventricle.
• Left Ventricle.

Apart from these four chambers the heart consists valves at junctions of auricles and ventricles and at junctions of right ventricle and pulmonary artery. These valves allow unidirectional flow of blood.