29. During which phase of mitosis does the nuclear membrane disappear?
Answer: D
The nuclear membrane disappears during prophase.
During prophase, the nuclear membrane breaks down, allowing the chromosomes to become visible as they condense and prepare for separation.
A) Metaphase
Metaphase is characterized by the alignment of chromosomes along the metaphase plate, but the nuclear membrane has already disappeared by this stage. Therefore, this option is incorrect as it does not describe the phase when the nuclear envelope dissolves.
B) Anaphase
Anaphase involves the separation of sister chromatids and their movement toward opposite poles of the cell. However, the nuclear membrane is not involved in this process since it has already disappeared during prophase. Thus, this option is also incorrect.
C) Telophase
Telophase is the stage where the nuclear membranes begin to reform around the separated sets of chromosomes. By this phase, the nuclear envelope is already absent, making this option incorrect regarding the disappearance of the nuclear membrane.
D) Prophase
Prophase is the correct answer as it is during this phase that the nuclear membrane dissolves, allowing the chromatin to condense into visible chromosomes. This is the defining action that marks the transition into the subsequent stages of mitosis.
Conclusion
The correct answer is prophase, as this is the only phase in which the nuclear membrane disappears. All other options describe phases where the nuclear membrane is either absent or reforming, making them incorrect in relation to the specific question about the disappearance of the nuclear envelope.