A-LevelBiologyThe mitotic cell cycle9700/22 · May/June 2018 · Q46 Marks

Fig. 4.1 is a photomicrograph showing some cells in interphase and some cells in stages of mitosis. [Figure 4.1]

(a)Choose from the cells labelled 1 to 5 in Fig. 4.1 to identify the cell in which: • the nuclear envelope is reassembling • the spindle begins to form • there is a high rate of transcription and translation[3]
(b)Cell 2 is in a stage of mitosis that occurs before the stage of mitosis shown in cell 1. Outline the changes that would occur from the stage of mitosis shown in cell 2 to the stage shown in cell 1.[2]
(c)Suggest why some cells in Fig. 4.1 appear empty, with no nucleus or chromosomes.[1]

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Mark scheme

Marking points from the official mark scheme (May/June 2018). The mark or mark type is shown in brackets.

[3] 1/4;
3;
5;
[2] two from:
centromere (of each chromosome) divides ; A sister chromatids separated at the centromere
spindle fibres, contract/shorten ; A spindle contracts
(sister/identical) chromatids / daughter chromosomes, pulled / move, to opposite poles ; A (sister) chromatids separated I chromosomes are at opposite poles
centromeres, leading (towards poles) / AW ; A ref. to V-shape / diagram
[1] one from:
not sectioned to include (nucleus) ;
did not take up the stain / not stained (correctly) / AW ;
AVP; e.g. cells may be dead I destroyed / eliminated / AW

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