A Level Biology Practice Exam

Which of the following statements about B lymphocytes is true?

1. They mature in the thymus gland.

2. They play a key role in cell-mediated immunity.

3. They produce antibodies in response to antigens.

4. They are always actively dividing.

The correct answer is: They produce antibodies in response to antigens.

B lymphocytes, also known as B cells, are crucial components of the adaptive immune response. Their primary function is to produce antibodies, which are specialized proteins that bind to specific antigens (foreign substances such as bacteria or viruses) to neutralize or mark them for destruction. When B cells encounter an antigen that matches their specific receptor, they can undergo activation, leading to their proliferation and differentiation into plasma cells. These plasma cells are responsible for the production and secretion of large quantities of antibodies. The maturation of B lymphocytes occurs in the bone marrow, not the thymus gland, which is where T lymphocytes mature. B cells are primarily involved in humoral immunity rather than cell-mediated immunity, which is predominantly carried out by T cells. Additionally, while B cells can divide and proliferate upon activation, they are not always actively dividing in a resting state; they are typically quiescent until they encounter their specific antigen. Thus, the statement about their role in producing antibodies in response to antigens accurately reflects the essential function of B lymphocytes in the immune system.