B cells and T cells are capable of recognizing foreign antigens because they have specific antigen in their plasma membrane.

B cells and T cells, two types of white blood cells, are key components in the immune system that help the body fight off infections. They are capable of recognizing foreign antigens due to the presence of specific antigen receptors on their plasma membrane. Here's a step-by-step explanation:

1. Antigen Recognition: Both B cells and T cells have unique antigen receptors on their surface. These receptors are proteins that can bind to a specific antigen. The shape of the receptor matches the shape of the antigen, much like a lock and key.

2. Activation: When an antigen binds to the receptor, it triggers the B cell or T cell to activate. This means the cell starts to divide and produce more cells to fight the infection.

3. Response: Activated B cells produce antibodies, which are proteins that can neutralize the antigen. T cells, on the other hand, can directly kill infected cells or help other immune cells respond to the antigen.

4. Memory: Some of the B cells and T cells become memory cells. These cells remember the specific antigen and can respond quickly if the body encounters the same antigen again in the future.

So, the specific antigen receptors in the plasma membrane of B cells and T cells enable them to recognize and respond to foreign antigens, playing a crucial role in the immune response.