The antibodies that can bind the largest number of antigens is ………while the antibody that is smallest in size is ………
Choose the option that correctly fills the blanks

Options

A. IgA, IgM
B. IgM, IgA
C. IgG, IgD
D. IgM, IgG

Answer

To solve the question, we need to identify two specific types of antibodies based on their characteristics: one that can bind to the largest number of antigens and one that is the smallest in size.

### Step-by-Step Solution:

1. **Understanding Antibodies**: Antibodies are proteins produced by the immune system to identify and neutralize pathogens like bacteria and viruses. They have specific structures that allow them to bind to antigens.

2. **Identifying the Antibody that Binds the Largest Number of Antigens**:
- Among the different classes of antibodies (IgA, IgD, IgE, IgG, IgM), IgM is known to be the first antibody produced during a primary immune response.
- IgM is unique because it exists in a pentameric form, meaning five antibody units are joined together. Each unit has two binding sites for antigens.
- Therefore, one IgM molecule can bind to a total of 10 antigens (5 units x 2 binding sites each).

3. **Identifying the Smallest Antibody**:
- IgG is the most abundant antibody in the blood and is known for its small size compared to other antibodies.
- It is so small that it can cross the placenta, providing passive immunity to the fetus.
- This characteristic makes IgG the smallest antibody among the classes.

4. **Filling in the Blanks**:
- From the analysis, we conclude that the antibody that can bind the largest number of antigens is **IgM** and the smallest antibody is **IgG**.

### Final Answer:
The antibodies that can bind the largest number of antigens is **IgM** while the antibody that is smallest in size is **IgG**.