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Cell and nuclear division: exam questions

8 questions, 26 marks. Write your answers on paper, then open each mark scheme.

Spec D2.1Questions and mark scheme (PDF)5 pages

Question 1

Paper 1A style

What achieves the splitting of the cytoplasm during cytokinesis in a plant cell?

  1. A ring of contractile actin and myosin proteins pinching the cell membrane inwards
  2. Vesicles that assemble sections of membrane and cell wall across the cell
  3. Spindle microtubules pulling the two halves of the cell apart
  4. The nuclear membrane re-forming across the middle of the cell
[1 mark]
Show mark scheme for question 1

Answer: B

Question 2

Paper 1A style

In a micrograph of a root tip, a cell shows two groups of V-shaped chromosomes moving towards opposite poles. Which phase of mitosis is the cell in?

  1. Prophase
  2. Metaphase
  3. Anaphase
  4. Telophase
[1 mark]
Show mark scheme for question 2

Answer: C

Question 3

Paper 1A style

An organism has a diploid number of 8. How many different combinations of chromosomes can be produced in its gametes by random orientation of bivalents alone?

  1. 4
  2. 8
  3. 16
  4. 256
[1 mark]
Show mark scheme for question 3

Answer: C (2⁴ = 16, since n = 4)

Question 4

Paper 2A style

Explain why cytokinesis is usually equal, and outline one example of unequal cytokinesis.

[3 marks]
Show mark scheme for question 4
  • each daughter cell must receive at least one mitochondrion / chloroplast / organelles that can only be made by division of pre-existing ones [1]
  • each daughter cell receives a nucleus / enough cytoplasm to survive OWTTE [1]
  • oogenesis: almost all cytoplasm passes to the (secondary) oocyte / ovum, small polar bodies formed [1]
  • OR budding in yeast: a small bud receives a nucleus and pinches off from the larger parent cell [1]
  • max 3

Question 5

Paper 2A style

Explain how non-disjunction can lead to a child with Down syndrome.

[4 marks]
Show mark scheme for question 5
  • non-disjunction is failure of chromosomes / chromatids to separate in meiosis [1]
  • homologous chromosomes fail to separate in meiosis I / sister chromatids fail to separate in meiosis II [1]
  • a gamete receives two copies of chromosome 21 / 24 chromosomes [1]
  • fertilised by a normal gamete with 23 chromosomes [1]
  • zygote has three copies of chromosome 21 / trisomy 21 / 47 chromosomes [1]
  • max 4

Question 6

Paper 1B style

HL only (what this means)HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels mean

Students counted cells in micrographs of normal tissue and of a tumour from the same organ (the data are for practice). (a) Calculate the mitotic index of the normal tissue. [1] (b) Calculate the mitotic index of the tumour tissue. [1] (c) Deduce, with a reason, which tissue is proliferating faster. [1] (d) Suggest two reasons why the mitotic index of a sample might be inaccurate. [2]

Cells counted in five fields of view
TissueCells in interphaseCells in mitosisTotal cells
Normal47525500
Tumour35288440
[5 marks]
Show mark scheme for question 6
  • (a) 25 ÷ 500 = 0.05 [1]
  • (b) 88 ÷ 440 = 0.20 [1] Accept answers as percentages (5%, 20%)
  • (c) tumour, because a higher proportion of its cells are in mitosis / higher mitotic index [1] ECF from (a) and (b)
  • (d) difficulty identifying early prophase / late telophase / cells overlapping [1]
  • only a small number of fields / cells counted, not representative [1]
  • cells counted twice / missed when counting [1]
  • max 2 for (d)

Question 7

Paper 2A style

HL only (what this means)HL only: additional Higher Level content, only for HL students. SL students can skip it. What the labels mean

Outline what happens during interphase and how cyclins control progression through the cell cycle.

[4 marks]
Show mark scheme for question 7
  • interphase consists of G1, S and G2 [1]
  • metabolically active / biosynthesis of proteins and other components / cell grows (in G1 and G2) [1]
  • DNA is replicated in S phase [1]
  • number of mitochondria / chloroplasts increases by growth and division [1]
  • concentrations of different cyclins rise and fall during the cycle [1]
  • a threshold level of a specific cyclin is needed to pass each checkpoint [1]
  • max 4

Question 8

Paper 2B style

Explain how meiosis halves the chromosome number and produces genetically different haploid nuclei.

[7 marks]
Show mark scheme for question 8
  • DNA is replicated before meiosis so each chromosome has two (sister) chromatids [1]
  • chromosomes condense by supercoiling (around histones) [1]
  • homologous chromosomes pair to form bivalents in prophase I [1]
  • crossing over between non-sister chromatids at chiasmata [1]
  • produces new combinations of alleles / recombinant chromatids [1]
  • bivalents line up at the equator in metaphase I in random orientation [1]
  • orientation of each bivalent is independent of the others, giving 2ⁿ combinations [1]
  • spindle microtubules / motor proteins move chromosomes to the poles [1]
  • homologous chromosomes separate in meiosis I / first segregation, halving the chromosome number [1]
  • sister chromatids separate in meiosis II / second segregation [1]
  • four haploid nuclei are produced from one diploid nucleus [1]
  • max 7
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