A-LevelBiologyThe mitotic cell cycle9700/22 · Oct/Nov 2017 · Q16 Marks

The root apical meristem is a region of undifferentiated cells in the root tips of plants. Mitosis occurs in this region.

(a)Fig. 1.1 is an image of the root tip of Allium as observed using a microscope with a low-power objective lens. [Figure 1.1] State which region, B, C, or D, should be chosen in order to observe the highest proportion of cells in stages of mitosis.[1]
(b)(i)Draw a labelled diagram to show the structure of a chromosome at late prophase of mitosis.[3]
(b)(ii)Describe the behaviour of the nuclear envelope during mitosis.[2]

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 (Oct/Nov 2017). The mark or mark type is shown in brackets.

[1] C;
[3] three from
two chromatids drawn ; must be connected at some point
(sister) chromatid label to correct structure ;
centromere label to correct structure ; A kinetochore
telomere label to end of chromatid ;
DNA and histone (proteins) label to chromatid ;
[2] two from
disassembles / breaks down / disintegrates / AW, at, prophase; A prometaphase
re-forms / re-assembles / AW, after anaphase / at telophase ;
if mp 1 and 2 not gained, one mark can be awarded for knowledge of disassembles and then reassembles
detail;
e.g. breakdown into vesicles
re-forms from vesicles / vesicles fuse to form new membranes
re-forms around both sets of (daughter) chromosomes

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