Choose the incorrect statement from the following

Options

A. In birds and mammals internal fertilisation takes place.
B. Colostrum contains antibodies and nutrients.
C. Polyspermy in mammals is prevented by the chemical changes in the egg surface.
D. In the human female, implantation occurs almost seven days after fertilisation.

Answer

To solve the question of identifying the incorrect statement from the given options, we will analyze each statement one by one:

### Step-by-Step Solution:

1. **Analyze Statement 1**:
- **Statement**: "In birds and mammals, internal fertilization takes place."
- **Explanation**: Internal fertilization is the process where the male and female gametes fuse inside the female body. This statement is true for both birds and mammals, as they both exhibit internal fertilization.

2. **Analyze Statement 2**:
- **Statement**: "Colostrum contains the antibodies and the nutrients."
- **Explanation**: Colostrum is the first milk produced after childbirth and is rich in antibodies and nutrients, providing immunity to the newborn. This statement is also true.

3. **Analyze Statement 3**:
- **Statement**: "Polyspermy in mammals is prevented by the chemical changes in the egg surface."
- **Explanation**: Polyspermy refers to the fertilization of an egg by more than one sperm. In mammals, polyspermy is prevented by a process called the cortical reaction, which involves the release of cortical granules that modify the egg surface. The statement incorrectly attributes the prevention of polyspermy to chemical changes in the egg surface rather than the cortical reaction. Thus, this statement is incorrect.

4. **Analyze Statement 4**:
- **Statement**: "In human females, implantation almost occurs 7 days after fertilization."
- **Explanation**: After fertilization, the zygote undergoes multiple divisions and develops into a blastocyst, which typically implants in the uterine wall about 7 days post-fertilization. This statement is true.

### Conclusion:
- After analyzing all four statements, we find that Statements 1, 2, and 4 are true, while Statement 3 is incorrect. Therefore, the answer to the question is Statement 3.

### Final Answer:
**The incorrect statement is: "Polyspermy in mammals is prevented by the chemical changes in the egg surface."**

---