A-LevelBiologyThe mitotic cell cycle9700/21 · May/June 2020 · Q211 Marks

2 Fig. 2.1 shows some stages of the cell cycle in the meristematic tissue in the root tip of a plant. Three of these stages, P, Q and R, are identified in Table 2.1. [Figure 2.1]

(a)Complete Table 2.1 by stating one feature, visible in Fig. 2.1, that is used to identify each stage. Table 2.1 cell | stage of cell cycle | reason P | prophase of mitosis | Q | metaphase of mitosis | R | interphase |[3]
(b)(i)Draw a labelled diagram to show one chromosome at metaphase of mitosis. On the chromosome you have drawn add labels to show: • the position of a telomere • a chromatid • the centromere.[4]
(b)(ii)State the type of protein that is associated with DNA in chromosomes.[1]
(b)(iii)Describe how the spindle is involved during the process of mitosis.[3]

This question uses a diagram from the original paper, which isn't shown here. Open the full paper from the past papers archive to see it.

Mark scheme

Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.

[3] P - chromosomes, arranged randomly / AW or idea that chromosomes present but not (yet) visible as consisting of two sister chromatids (joined by centromere); A description related to idea of chromosomes becoming visible / chromatin condensing
Q- chromosomes are, arranged / aligned / AW, at the, (cell / spindle) equator / metaphase plate; A equatorial plate
R - no chromosomes visible / nucleolus is present / chromatin not condensed / euchromatin present ;
[4] drawing two chromatids of identical length joined at the centromere ;
labels chromatid; one label line is sufficient R if second line drawn to arm of sister chromatid centromere ;
telomere;
[1] histone(s) ; A highly basic (protein)
[3] accept spindle fibres/microtubules as alternative to spindle max 2 if stages are named and are incorrect
any three from: (prophase) attachment to centromere of each chromosome ; A ref. to kinetochore in correct context
(prophase) arranging / orientating / AW, chromosomes at the, equator / metaphase plate / AW ; A ref. to metaphase in correct context
(anaphase) centromere division / separation of sister chromatids ;
(anaphase) pulling, chromatids / daughter chromosomes, apart/ towards poles ;
(because) spindle fibres contract / (as) lengths of microtubules decreases / microtubules are disassembled ;
(elongates in telophase to) push, poles / nuclei, apart;

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