Read the following statements
(a) Complete disintegration of the nuclear envelope marks the start of the second phase of mitosis.
(b) Metaphase chromosome is made up of one sister chromatid

Options

A. Only (b) is correct
B. Both (a) & (b) are incorrect
C. Only (a) is correct
D. Both (a) & (b) are correct

Answer

To analyze the given statements, we will break down each statement and evaluate its accuracy based on our understanding of the cell cycle and mitosis.

### Step-by-Step Solution:

**Step 1: Evaluate Statement (a)**
- The statement claims that "Complete disintegration of the nuclear envelope marks the start of the second phase of mitosis."
- In the cell cycle, mitosis consists of several phases: prophase, metaphase, anaphase, and telophase.
- During prophase, the nuclear envelope begins to break down, and by the end of prophase, it is completely disintegrated.
- The second phase of mitosis is metaphase, which follows prophase.
- Therefore, the complete disintegration of the nuclear envelope does indeed mark the transition from prophase to metaphase.

**Conclusion for Statement (a):** This statement is **correct**.

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**Step 2: Evaluate Statement (b)**
- The statement claims that "Metaphase chromosome is made up of one sister chromatid."
- During metaphase, chromosomes are highly condensed and are visible under a microscope.
- Each chromosome consists of two sister chromatids that are joined at the centromere.
- Therefore, a metaphase chromosome is not made up of one sister chromatid; it consists of two sister chromatids.

**Conclusion for Statement (b):** This statement is **incorrect**.

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### Final Conclusion:
- Statement (a) is correct.
- Statement (b) is incorrect.

Thus, the answer to the question is that only statement (a) is correct.

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