A-LevelBiologyThe mitotic cell cycle9700/42 · Feb/Mar 2023 · Q58 Marks

Meiosis is described as a reduction division because the number of chromosomes in the daughter cells is reduced by half.

(a)Table 5.1 describes some of the events that take place during four of the different stages of meiosis in an animal cell. Table 5.1 stage of meiosis | spindle fibres | diagram -----------------|-------------------------------------------------------------------------------------|---------------------- metaphase I | attach to centromeres and arrange homologous pairs of chromosomes at the equator of the cell | [Figure for Metaphase I] anaphase I | | [Figure for Anaphase I] [BLANK] | re-form spindle in daughter cells | [Figure for Prophase II] telophase II | disassemble | [BLANK] Complete Table 5.1 by: • outlining the behaviour of the spindle fibres during anaphase I • identifying the stage of meiosis in which spindle fibres re-form the spindle in daughter cells • drawing a diagram to show telophase II. You do not need to add labels to your diagram showing telophase II.[4]
(b)Explain the need for a reduction division during meiosis.[4]

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Mark scheme

Marking points from the official mark scheme (Feb/Mar 2023). The mark or mark type is shown in brackets.

[4] (a) stage of meiosis: anaphase I, spindle fibres: (contract to) pull, centromeres / chromosomes, towards poles / to centrioles ;
[4] (a) stage of meiosis: prophase II ; spindle fibres: re-form spindle in daughter cells
[4] (a) stage of meiosis: telophase II, diagram: (forming) four daughter cells ; two single chromosomes inside a (re-forming) nuclear envelope;
[4] (b) any four from:
[4] (b) 1 (meiosis / reduction division) produces gametes ;
[4] (b) 2 (two) gametes fuse / fertilisation occurs, to form a zygote ;
[4] (b) 3 zygote will have maternal and paternal chromosomes / AW;
[4] (b) 4 gametes, are haploid / are n / have half the normal number (of chromosomes);
[4] (b) 5 so the zygote, is diploid / 2n;
[4] (b) 6 prevents, doubling of chromosome number / polyploidy / having too many chromosomes or allows chromosome number to remain constant ;

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