CAIE A Level Biology 9700 · The mitotic cell cycle
During prophase of mitosis, a living animal cell is observed using fluorescence microscopy. Initially, the nuclear envelope appears as a continuous ring around the chromosomes, and no spindle fibres are visible. As prophase progresses, the nuclear envelope breaks down and spindle fibres begin to extend from the centrosomes. Explain why these changes to the nuclear envelope and spindle are essential for the correct alignment of chromosomes at the metaphase plate.
5 marks, so the mark scheme is looking for about 5 separate creditworthy points. Making the same point twice in different words earns it once.
Explain means: Give the reasons or the mechanism: why or how something happens. Link each point to the next with because, so or which means. A list of facts with no links usually loses the reasoning marks.
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