Which phase of mitosis is the longest?

Prophase is identified as the longest phase of mitosis due to several key processes that occur during this stage, which require a considerable amount of time to complete. During prophase, the chromatin condenses into visible chromosomes, each consisting of two sister chromatids. The nuclear envelope begins to break down, allowing the microtubules to access the chromosomes. In addition to these changes, the mitotic spindle starts to form from the centrosomes, which move apart and begin to organize the microtubules.

This phase involves significant preparation for the subsequent stages of mitosis. The substantial transformations occurring in prophase—like chromosome condensation and spindle formation—take longer than the events that characterize the later phases of mitosis, such as alignment of chromosomes at the metaphase plate, separation of chromatids during anaphase, or the reformation of the nuclear envelope in telophase. Therefore, the extended duration of these preparatory activities contributes to prophase being the longest phase in the mitotic process.