CBSE Class 11 Biology Chapter 18: Body Fluids and Circulation NCERT Solutions

Solution: The formed elements of blood are the cellular components suspended in the plasma. These include erythrocytes, leukocytes, and platelets. Each has distinct functions:

1. Erythrocytes (Red Blood Cells - RBCs): These are the most numerous cells in the blood and are rich in a red pigment called haemoglobin. Their primary function is to transport oxygen from the lungs to all tissues of the body and to assist in transporting carbon dioxide back to the lungs. They are produced mainly in the bone marrow.

2. Leukocytes (White Blood Cells - WBCs): These are colourless cells that are larger than RBCs and lack haemoglobin. They are the body's primary defense against infection and disease. WBCs are broadly classified into two main categories:

Granulocytes: These include neutrophils, eosinophils, and basophils. Neutrophils are phagocytic and engulf bacteria. Eosinophils combat parasitic infections and are involved in allergic reactions. Basophils release histamine and other inflammatory mediators.

Agranulocytes: These include lymphocytes and monocytes. Lymphocytes are crucial for the immune system, producing antibodies and cellular immunity. Monocytes are large phagocytic cells that engulf pathogens and cellular debris.

3. Platelets (Thrombocytes): These are small, irregular-shaped cell fragments derived from megakaryocytes. Their main function is to play a critical role in blood clotting (coagulation) by forming a plug at the site of injury and releasing factors that initiate the clotting cascade, thus preventing excessive bleeding.

Solution: Plasma proteins are vital components of blood plasma, constituting about 6.8% of its volume. They perform several critical functions essential for maintaining homeostasis and physiological processes:

1. Fibrinogens: These proteins, synthesized by the liver, are essential for blood coagulation. They form fibrin threads that create the meshwork of a blood clot, stopping bleeding.

2. Globulins: This group includes antibodies (immunoglobulins) that are crucial for the body's immune defense system, protecting against infections. Other globulins also play roles in transporting lipids, hormones, and other substances.

3. Albumins: These are the most abundant plasma proteins, also synthesized by the liver. Albumins are primarily responsible for maintaining the osmotic pressure of the blood (colloid osmotic pressure). This pressure is critical for regulating the distribution of water between the blood plasma and the interstitial fluid, thus preventing excessive fluid accumulation in tissues (edema) and maintaining blood volume.

In summary, plasma proteins are indispensable for blood clotting, immunity, transport, and maintaining fluid balance within the circulatory system.

Solution: The correct matching of Column I with Column II is as follows:

Column I | Column II

1. Eosinophils | Resist Infections (specifically involved in allergic responses and defense against parasites)
2. RBC | Gas transport (primarily oxygen)
3. AB Group | Universal Recipient (can receive blood from A, B, AB, and O groups)
4. Platelets | Coagulation (essential for blood clotting)
5. Systole | Contraction of Heart (the phase of the cardiac cycle where the heart muscle contracts)

Solution: Blood is considered a specialized type of connective tissue for several key reasons:

Firstly, like other connective tissues, blood originates from the mesoderm, which is one of the primary germ layers in embryonic development. This shared embryonic origin is a fundamental characteristic of connective tissues.

Secondly, blood possesses the defining features of connective tissue: it consists of cells (red blood cells, white blood cells, and platelets) that are dispersed within an extracellular matrix. This matrix in blood is known as plasma, a fluid component that suspends the cellular elements.

Furthermore, blood serves a connective function within the body. It connects various organ systems by transporting essential substances such as oxygen, nutrients, hormones, and antibodies to all parts of the body. Simultaneously, it removes metabolic waste products like carbon dioxide and urea from the tissues, facilitating their excretion. This transport and connection role is characteristic of connective tissues that link and support different parts of the organism.