Final answer:
The Fc region of antibodies is made up of constant heavy chains. This region is critical for the immune response as it allows effector cells to bind to antibody-coated pathogens.
Step-by-step explanation:
The Fc region of antibodies is formed by the two heavy chains coming together, usually linked by disulfide bonds. Specifically, the constant region of the heavy chain, which consists of three to four independent domains (CH₁, CH₂, CH₃, and sometimes CH₄), is what comprises the Fc region. Therefore, the correct answer to 'The Fc region of antibodies is made up of what?' is (a) Constant heavy chains.
It is important to note that the constant regions of the light chains do not contribute to the Fc region. The Fc portion of an antibody plays a critical role as many effector cells of the immune system have Fc receptors that can bind to antibody-coated pathogens. This interaction significantly enhances the specificity and effectiveness of the immune response.