A : in morula stage the cells divide without any increase in size
R : zona pellucida remains intact till cleavage is completed

Options

A. If both A and R are true and R is the correct explanation of A
B. If both A and R are true but R is not the correct explanation of A
C. If A is true and R is false
D. If both A and R are false

Answer

To solve the assertion and reason question, we will analyze both statements step by step.

### Step 1: Analyze the Assertion
**Assertion (A)**: In the morula stage, the cells divide without any increase in size.

- **Explanation**: The morula stage is an early stage of embryonic development that occurs after several rounds of cell division (cleavage) following fertilization. During this stage, the zygote divides into multiple smaller cells called blastomeres. Importantly, these divisions occur without an increase in the overall size of the embryo. This is because the zona pellucida, a protective layer surrounding the embryo, restricts the expansion of the cells. Therefore, the assertion is correct.

### Step 2: Analyze the Reason
**Reason (R)**: Zona pellucida remains intact till cleavage is completed.

- **Explanation**: The zona pellucida is a glycoprotein layer that surrounds the developing embryo. It serves several functions, including preventing polyspermy and protecting the embryo during early development. The zona pellucida remains intact throughout the cleavage stages until the embryo reaches the blastocyst stage, at which point it will hatch out of this layer. Thus, this statement is also correct.

### Step 3: Determine the Relationship Between Assertion and Reason
- While both the assertion and reason are true, the reason does not explain why the cells divide without an increase in size. The assertion discusses the size of the cells during the morula stage, while the reason discusses the integrity of the zona pellucida. Therefore, the reason does not provide a direct explanation for the assertion.

### Conclusion
Both statements are true, but the reason is not the correct explanation for the assertion.

**Final Answer**: Both A and R are true, but R is not the correct explanation of A.

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