Which of the following statements is incorrect?

Options

A. Placenta allows exchange of materials between mother and fetus.
B. The fetal part of the placenta consists of the cells of the chorion which produce projections called chorionic villi.
C. Antibody cannot cross the placenta from mother to fetus.
D. Placenta secretes pregnancy hormones required for supporting fetal growth and metabolic changes in mother during pregnancy.

Explanation

To determine which statement is incorrect regarding reproduction in organisms, we will analyze each statement provided in the question.

### Step-by-Step Solution:

1. **Statement Analysis**:
- **Statement 1**: "Placenta allows exchange of materials between mother and fetus."
- This statement is **correct**. The placenta facilitates the transfer of nutrients, gases (like oxygen and carbon dioxide), and waste products between the mother and the fetus.

2. **Statement 2**: "The fetal part of the placenta consists of the cells of the chorion, which produces projections called chorionic villi."
- This statement is **correct**. The chorion is indeed the outermost layer of the embryo, and it forms chorionic villi that extend into the maternal tissue to facilitate nutrient and gas exchange.

3. **Statement 3**: "Antibodies cannot cross the placenta from mother to fetus."
- This statement is **incorrect**. In fact, many antibodies, particularly IgG, can cross the placenta and provide passive immunity to the fetus. This is a crucial aspect of fetal development.

4. **Statement 4**: "The placenta secretes pregnancy hormones required for supporting fetal growth and metabolic changes in the mother during pregnancy."
- This statement is **correct**. The placenta produces several hormones, including human chorionic gonadotropin (hCG), progesterone, and estrogen, which are essential for maintaining pregnancy and supporting fetal development.

### Conclusion:
The incorrect statement is **Statement 3**: "Antibodies cannot cross the placenta from mother to fetus."

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