Tag: zoology

A- Prothrombin is converted into thrombin by prothrombinase & then thrombin transforms fibrinogen into fibrin.

The letter T in T-lymphocyte refers to Thymus. T cells or T lymphocytes are a type of lymphocyte, that play a central role in cell-mediated immunity. They can be distinguished from other lymphocytes, such as B cells and natural killer cells, by the presence of a T-cell receptor on the cell surface. They are called T cells because they mature in the thymus.

A lymphocyte is not a granulocyte. Granulocytes are a category of white blood cells characterized by the presence of granules in their cytoplasm. There are three principal types of granulocytes- basophil granulocytes, eosinophil granulocytes and neutrophil granulocytes. Lymphocytes and monocytes are the agranulocytes. Thus, the correct answer is option A.

There are two main types of lymphocytes: B cells and T cells. The B cells make antibodies that attack bacteria and toxins while the T cells attack body cells themselves when they have been taken over by viruses or have become cancerous. Lymphocytes are small white blood cells that play a large role in defending the body against disease. Hence, the lymphocytes are responsible for immune responses.

A lymphocyte is any of the three kinds as B-cells, T-cells and natural killer or NK cells. All these are agranulocytes.
Eosinophils are granulocytes, that develop during hematopoiesis in the bone marrow.
Basophils are granulocytes i.e., they contain large cytoplasmic granules in the cell nucleus and it stores histamine (a vasodilator), a chemical, which is secreted by the cells, when stimulated, which promotes blood flow to tissues.
Neutrophils are the most abundant type of WBCs. They are phagocytic in nature and are able to engulf foreign substances (like bacteria).

Monocytes are a type of WBCs. Monocytes mature in different types of macrophages at different locations. Monocytes and their macrophages serve three main functions as phagocytosis, antigen presentation and cytokine production.
Lymphocytes are B-cells or T-cells and they have receptors on their surface and are able to bind antigens and thus help the foreign substance to get removed from the body. They are not phagocytic in nature.
Mast cell is the part of immune system that contains granules rich in histamine and heparin. They can also participate in the direct killing of organisms by phagocytosis.
Neutrophils are the most abundant type of WBCs. They are phagocytic in nature and are able to engulf foreign substances (like bacteria).
Thus, the correct answer is option B.

B-cells (or B-lymphocytes) and T-cells (or T-lymphocytes) are the lymphocytes, that are mature and have receptors on their surface and thus are able to bind to antigens and help the foreign substance to be removed from the body.
Thymocytes are the developing T-cells of hematopoietic origin and are immature.
Leukocytes are the mature white blood cells.
Thus, the correct answer is the option (C), 'Thymocytes'.

Acquired immunity is a type of immunity which is not present at birth. It is learned. As a person's immune system encounters various antigens, the components of acquired immunity find the best way to attack each antigen and begins to develop a memory for that antigen. It is also called specific immunity. Acquired immunity takes time to develop after initial exposure to a new antigen.
Lymphocytes are the type of white blood cell responsible for acquired immunity. Acquired immune response begins with antibodies, produced by B cells or B lymphocytes.
Thus, the correct answer is the option (D), 'Lymphocytes'.