A Level Biology Practice Exam

What does clonal selection theory propose?

1. Exposure to random antigens leads to proliferation

2. Specific antigens stimulate the proliferation of antibody-forming cells

3. All cells can become antibody-producing cells

4. Increased exposure to antigens reduces immunity

The correct answer is: Specific antigens stimulate the proliferation of antibody-forming cells

Clonal selection theory proposes that specific antigens stimulate the proliferation of antibody-forming cells. This concept is fundamental to understanding how the immune system recognizes and responds to pathogens. When a specific antigen enters the body, it binds to a corresponding B cell that has a receptor for that antigen. This binding activates the B cell, leading to its proliferation and differentiation into plasma cells that produce antibodies specific to that antigen. The theory highlights the specificity of the immune response, as only those B cells that can recognize the antigen will be activated and multiply. The other options do not accurately reflect the principles of clonal selection. Random exposure to antigens does not lead to proliferation; rather, it is the specific recognition of an antigen by a unique B cell that drives the immune response. Not all cells can become antibody-producing cells, as only B cells have the necessary machinery to produce antibodies. Lastly, increased exposure to antigens does not reduce immunity; in fact, it often enhances it by strengthening the immune memory and response to known pathogens.