Questions: OK, let's check how well you're following so far. What cells are classed as lymphocytes? Click the VIEW THEORY button to get some guidance with the question. a) Cells that arise from a myeloid progenitor cell, for example, natural killer cells and macrophages b) Cells that arise from a lymphoid progenitor cell, for example, B cells and natural killer cells c) Cells that arise from a lymphoid progenitor cell, for example, dendritic cells and T cells d) Cells that arise from a myeloid progenitor cell, for macrophages and mast cells

The answer is the second one (b): Cells that arise from a lymphoid progenitor cell, for example, B cells and natural killer cells.

Explanation for each option:

a) Cells that arise from a myeloid progenitor cell, for example, natural killer cells and macrophages - This is incorrect because natural killer cells arise from a lymphoid progenitor cell, not a myeloid progenitor cell. Macrophages do arise from a myeloid progenitor cell, but they are not classified as lymphocytes.

b) Cells that arise from a lymphoid progenitor cell, for example, B cells and natural killer cells - This is correct. Lymphocytes are a type of white blood cell that arise from a lymphoid progenitor cell. B cells and natural killer cells are both types of lymphocytes.

c) Cells that arise from a lymphoid progenitor cell, for example, dendritic cells and T cells - This is partially correct because T cells are lymphocytes that arise from a lymphoid progenitor cell. However, dendritic cells are not classified as lymphocytes; they can arise from both myeloid and lymphoid progenitors.

d) Cells that arise from a myeloid progenitor cell, for macrophages and mast cells - This is incorrect because neither macrophages nor mast cells are classified as lymphocytes. They both arise from a myeloid progenitor cell.

In summary, lymphocytes are cells that arise from a lymphoid progenitor cell, and examples include B cells, T cells, and natural killer cells.