Choose the incorrect statement(s) from the following.
I. Fusion of male and female gametes is called fertilization.
II. Plasmogamy refers to fusion of protoplast of two cells.
III. Karyogamy refers to formation of zygote.

Options

A. Only I
B. II and III
C. Only III
D. I and II

Answer

To solve the problem, we need to analyze each statement provided and determine which ones are incorrect.

### Step-by-Step Solution:

1. **Statement I: Fusion of male and female gametes is called fertilization.**
- This statement is correct. Fertilization is defined as the process where a male gamete (sperm) fuses with a female gamete (egg) to form a zygote.

2. **Statement II: Plasmogamy refers to fusion of protoplast of two cells.**
- This statement is also correct. Plasmogamy is the process of fusion of the cytoplasm (protoplast) of two cells, which is a key step in the formation of a zygote in sexual reproduction.

3. **Statement III: Karyogamy refers to formation of zygote.**
- This statement is incorrect. Karyogamy specifically refers to the fusion of the nuclei of two gametes. While karyogamy is involved in the formation of a zygote, it is not accurate to say that karyogamy itself refers to the formation of a zygote. The zygote is formed after both plasmogamy and karyogamy occur.

### Conclusion:
- The incorrect statement is **Statement III**.

### Summary of Incorrect Statements:
- **Only Statement III is incorrect.**