Agranulocytes are leukocytes that either lack granules in their cytoplasm or have granulocytes that are not as apparent as in the other cell types. Agranulocytes are basically of two types - monocytes and lymphocytes. They are both involved in the immune responses of the body.

Thus, the correct answer is 'Lymphocytes.'

Lymphocytes are one of the main types of immune cells. Lymphocytes are divided mainly into B and T cells. B lymphocytes produce antibodies - proteins (gamma globulins) that recognize foreign substances (antigen) and attach themselves to them. B lymphocytes (or B cells) are each programmed to make one specific antibody.

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'.

Lymphocytes are of two major types, ‘B’ and ‘T’ forms. When B lymphocytes recognize foreign antigen they release antibodies. The B cells are known as plasma cells. Hence the formation of antibodies is the function of lymphocytes.

White blood cells are an important part of the immune system. Lymphocytes are one of several different types of white blood cells. Lymphocytes are of two types B cells and T cells. When a macrophage engulfs bacteria B cells release antibodies which cause the destruction of bacteria. The T cells destroy the infectious bacteria by killing the body cells that are affected.

Lymphocytes are one of several different types of white blood cells. Lymphocytes are of two types B cells and T cells. When a macrophage engulfs organisms, B cells (humoral immunity) release antibodies which cause the destruction of bacteria. The T cells (cell-mediated immunity) destroy the infectious organisms by killing the body cells that are affected. Hence lymphocytes is a unit of the immune system.

The lymph fluid (P) inside the lymph nodes contains lymphocytes, a type of white blood cell, which continuously recirculates through the lymph nodes and the bloodstream. Molecules found on bacteria cell walls or chemical substances secreted from bacteria, called antigens, are taken up by antigen cells into the lymph system and then into lymph nodes. In response to the antigens, the lymphocytes in the lymph node make antibodies which will go out of the lymph node into circulation, target the pathogens producing the antigens by targeting them for destruction by other cells and complement.

The spleen acts to help keep the blood free of unwanted substances, including wastes and infecting organisms. The blood is delivered to it by the splenic artery and passes through smaller branch arteries into a network of channels lined with leukocytes, known as phagocytes. Red blood cells disintegrate in spleen. 

A) The statement is true as WBCs are called leukocytes because they are colorless and do not possess any pigments.

The blood cells are of three major types they are erythrocytes(RBC), leucocytes(WBC) and platelets. Two main categories of WBCs are granulocytes and agranulocytes. Neutrophils, eosinophils, and basophils are different types of granulocytes, while lymphocytes and monocytes are the agranulocytes.  Lymphocytes are of two major types – ‘B’ and ‘T’ forms. Both B and T lymphocytes are responsible for immune responses of the body.B lymphocytes are responsible for humoral immunity and T lymphocytes in cell-mediated immunity. Hence lymphocytes are not phagocytic.