Cell Division
Level 2 Test Paper (Recall)
Time Limit: 30 minutes Total Marks: 40
Instructions: Answer all questions. Write clearly and use correct biological terminology. Diagrams may be used where helpful.
Question 1. [4 marks] State the four phases of the cell cycle in the correct order, and describe one key event that occurs in each phase.
Question 2. [4 marks] Define the following terms relating to chromosome structure: (a) chromatid (b) sister chromatids (c) centromere (d) diploid cell
Question 3. [5 marks] Describe the four stages of mitosis (PMAT), stating the main event of each stage. (1 mark per stage correctly described + 1 mark for correct order.)
Question 4. [4 marks] Compare cytokinesis in animal cells and plant cells. Give two differences.
Question 5. [4 marks] (a) State two functions of mitosis in a multicellular organism. [2] (b) Explain how uncontrolled cell division can lead to cancer. [2]
Question 6. [4 marks] (a) Name the three main cell cycle checkpoints. [3] (b) State one general purpose of these checkpoints. [1]
Question 7. [4 marks] Explain the role of cyclins and cyclin-dependent kinases (CDKs) in controlling the cell cycle.
Question 8. [5 marks] Complete the comparison table between mitosis and meiosis. (1 mark each)
| Feature | Mitosis | Meiosis |
|---|---|---|
| Number of divisions | (i) | (ii) |
| Number of daughter cells | (iii) | (iv) |
| Chromosome number of daughter cells (vs parent) | same | (v) |
Question 9. [4 marks] (a) Define crossing over and state where it occurs. [2] (b) Explain two ways meiosis generates genetic variation. [2]
Question 10. [2 marks] Define nondisjunction and state one consequence in humans.
END OF PAPER
Answer keyMark scheme & solutions
Question 1. [4 marks] — 1 mark each (event + correct phase)
- G1 (Gap 1): cell grows, synthesises proteins/organelles, increases in size. ✓
- S (Synthesis): DNA replication — each chromosome copied to form two sister chromatids. ✓
- G2 (Gap 2): further growth, synthesis of proteins needed for division, organelles duplicate; checks DNA. ✓
- M (Mitosis/Mitotic phase): nuclear division (mitosis) and cytokinesis. ✓ Why: Interphase (G1, S, G2) prepares the cell; M phase divides it.
Question 2. [4 marks] — 1 mark each (a) Chromatid: one of the two identical DNA copies making up a replicated chromosome. ✓ (b) Sister chromatids: the two identical chromatids of a replicated chromosome, joined at the centromere. ✓ (c) Centromere: the constricted region of a chromosome where sister chromatids are joined and spindle fibres (via kinetochore) attach. ✓ (d) Diploid cell: a cell containing two complete sets of chromosomes (2n), one from each parent. ✓
Question 3. [5 marks]
- Prophase: chromosomes condense/become visible; nuclear envelope breaks down; spindle begins to form. ✓
- Metaphase: chromosomes line up along the metaphase plate (cell equator); spindle fibres attach to centromeres. ✓
- Anaphase: sister chromatids separate and are pulled to opposite poles. ✓
- Telophase: chromatids reach poles, decondense; nuclear envelopes reform; spindle breaks down. ✓
- Correct order maintained (PMAT). ✓ Why: Order ensures each daughter nucleus receives one full identical chromosome set.
Question 4. [4 marks] — 2 marks per correct difference (any two)
- Animal cells: cell membrane pinches inward forming a cleavage furrow; Plant cells: a cell plate forms in the middle and grows outward to form a new cell wall. ✓✓
- Animal division occurs because there is no rigid wall; plant cells cannot pinch due to the rigid cell wall, so a plate/wall is built. ✓✓ Why: The presence of a cell wall dictates the mechanism.
Question 5. [4 marks] (a) Any two [1 each]: growth of organism; repair of tissues/wound healing; replacement of dead/worn cells; asexual reproduction. ✓✓ (b) Cancer arises when mutations disrupt cell cycle control/checkpoints ✓, causing uncontrolled, continuous cell division forming a tumour. ✓ Why: Loss of checkpoint regulation → unregulated proliferation.
Question 6. [4 marks] (a) [1 each]: G1 checkpoint (restriction point); G2 checkpoint; M (spindle/metaphase) checkpoint. ✓✓✓ (b) They ensure the cell only proceeds if conditions are correct (e.g. DNA undamaged/replicated correctly, chromosomes correctly attached), preventing errors. ✓
Question 7. [4 marks]
- Cyclins are regulatory proteins whose concentration rises and falls through the cycle. ✓
- They bind to and activate CDKs (cyclin-dependent kinases). ✓
- Active cyclin–CDK complexes phosphorylate target proteins, triggering events/transitions of the cell cycle. ✓
- CDKs are inactive without cyclin, so this controls timing/progression past checkpoints. ✓
Question 8. [5 marks] — 1 mark each
| Feature | Mitosis | Meiosis |
|---|---|---|
| Number of divisions | 1 | (ii) 2 |
| Number of daughter cells | (iii) 2 | (iv) 4 |
| Chromosome number vs parent | same | (v) halved (haploid) |
(i) 1 ✓ (ii) 2 ✓ (iii) 2 ✓ (iv) 4 ✓ (v) halved/haploid ✓
Question 9. [4 marks] (a) Crossing over: the exchange of genetic material (segments) between non-sister chromatids of homologous chromosomes ✓; occurs during prophase I of meiosis (at chiasmata). ✓ (b) Any two [1 each]: crossing over (recombination); independent assortment of homologous chromosomes/chromatids at metaphase; random fertilisation (also acceptable: new allele combinations). ✓✓
Question 10. [2 marks]
- Nondisjunction: failure of homologous chromosomes (in meiosis I) or sister chromatids (meiosis II) to separate correctly. ✓
- Consequence: gametes/cells with abnormal chromosome number (aneuploidy), e.g. Down syndrome (trisomy 21). ✓
[
{"claim":"Meiosis produces 4 daughter cells from 1 parent cell","code":"parent=1; divisions=2; daughters=parent*2**divisions; result = (daughters==4)"},
{"claim":"Mitosis produces 2 daughter cells (1 division)","code":"parent=1; divisions=1; daughters=parent*2**divisions; result = (daughters==2)"},
{"claim":"Meiosis halves chromosome number: 2n=46 gives n=23","code":"diploid=46; haploid=diploid/2; result = (haploid==23)"},
{"claim":"Cell cycle phases G1,S,G2 form interphase; total named cell-cycle phases =4","code":"phases=['G1','S','G2','M']; interphase=[p for p in phases if p!='M']; result = (len(phases)==4 and len(interphase)==3)"}
]