OxfordAQA International AS and A-level Biology: Cell division, mutation and cancer (9610) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions cover sections 3.2.10 and 3.2.11 and Required practical 4 of the OxfordAQA International AS and A-level Biology (9610) specification, Version 5.1 (Unit 2). Read the study guide and revision notes first. Course pages: hub and checklist. Not sure where to start? Try the free diagnostics.

Questions

1. State what happens in each of the G1, S and G2 phases of interphase. [3]

2. A culture of dividing cells has a cell cycle of 12 hours. A sample of 240 cells is classified: 108 in G1, 60 in S, 42 in G2 and 30 in mitosis.

(a) Calculate the time spent in S phase and in mitosis. [2] (b) State the assumption made in using these counts. [1] (c) Give one process that occurs in G2. [1]

3. The DNA mass in one nucleus was measured through a 10 hour cycle. It was 4.6 pg from 0 to 3 hours, rose steadily to 9.2 pg at 7 hours, stayed at 9.2 pg until 9.5 hours, then fell to 4.6 pg at 10 hours.

(a) Name the phase between 3 and 7 hours and explain the evidence. [2] (b) Explain the fall in DNA mass between 9.5 and 10 hours. [2]

4. Four cells from a root tip squash were described. Cell A: chromosomes in two groups at opposite ends, nuclear envelopes reforming. Cell B: chromosomes in a line across the middle. Cell C: short, thick chromosomes scattered, each of two chromatids. Cell D: V-shaped chromosomes moving apart.

(a) Put the cells in order and name each stage. [2] (b) Explain how the movement seen in cell D happens. [3]

5. (a) Describe binary fission. [3] (b) A culture has 25 bacteria. Each divides every 30 minutes. Calculate the number after 4 hours. [2]

6. Explain how a gene for antibiotic resistance could pass from one species of bacterium to another, and why this is called horizontal gene transmission. [4]

7. Part of an mRNA is AUG GAA CCA UUU CGC ACU UAA. Codons: AUG Met; GAA Glu; CCA and CCG Pro; UUU and UUC Phe; CGC Arg; ACU Thr; AAC Asn; CAU His; GCA Ala; CUU Leu; UAA stop.

(a) Predict the amino acid sequence if base 9 (A) is replaced by G. [2] (b) Predict the effect if base 4 (G) is replaced by U. [2] (c) Predict the sequence if base 4 is deleted. [2]

8. Define a mutagen, say when spontaneous mutations arise, and explain why a substitution may not change a protein. [3]

9. (a) Give two differences between benign and malignant tumours. [2] (b) Explain how a mutated proto-oncogene can lead to a tumour. [2] (c) Explain how a mutated tumour suppressor gene can lead to a tumour. [2]

10. The illustrative table shows melanoma cases per 100 000 fair-skinned adults per year by daily sun exposure: under 1 hour 8.2; 1 to 3 hours 11.5; 3 to 5 hours 19.7; over 5 hours 26.9.

(a) Describe the relationship. [2] (b) Calculate how many times higher the incidence is for over 5 hours than under 1 hour. [2] (c) Evaluate the claim that the data show sunlight causes melanoma. [3]

11. Drug X blocks DNA replication. Drug Y stops spindle formation.

(a) State the phase each drug acts in and explain why dividing cells are harmed. [4] (b) Suggest why hair loss is a side effect. [2]

12. A root tip squash was made. An untreated tip had 29 cells in mitosis among 242 counted. A tip treated with chemical Z had 52 in mitosis among 260.

(a) Calculate both mitotic indices as percentages. [2] (b) Describe how the squash was prepared. [3] (c) Suggest one improvement to make the comparison more reliable. [1]

Answers

1. G1: cell grows and makes protein and more organelles such as mitochondria and ribosomes [1]. S: DNA is replicated [1]. G2: rapid growth and protein synthesis continue [1]. [3] Examiner insight: Three separate phases each need their own statement; a general comment such as “the cell prepares” does not distinguish them.

2. (a) S: 60 / 240 × 12 = 3.0 hours [1]. Mitosis: 30 / 240 × 12 = 1.5 hours [1]. (b) Cells are spread evenly through the cycle, so the fraction of cells in a phase equals the fraction of time [1]. (c) Rapid cell growth or protein synthesis [1]. Examiner insight: Show the fraction and the multiplication so your working is clear, and give units (hours) with each value.

3. (a) S phase [1]. DNA mass doubles from 4.6 pg to 9.2 pg, showing DNA replication [1]. (b) The cell divides, so the DNA is shared between the two daughter cells [1], and each receives half the mass, 4.6 pg [1]. Examiner insight: Quote the figures from the data when explaining; saying only “DNA goes up” earns less than naming the values and linking them to replication.

4. (a) C (prophase), B (metaphase), D (anaphase), A (telophase) [1] for the correct order, [1] for all four names correct. (b) Spindle fibres are attached to centromeres [1]. The centromeres divide and the fibres shorten [1], pulling the chromatids to opposite poles, so each pole gets one copy of every chromosome [1]. [5] Examiner insight: Link the fibres to the centromere and say they shorten; “the spindle pulls them” with no detail is too vague to separate the points.

5. (a) The circular DNA replicates [1]. Plasmids replicate [1]. The cytoplasm divides to give two daughter cells, each with one copy of the circular DNA, and plasmid number may vary [1]. (b) 4 hours = 240 minutes, so 240 / 30 = 8 divisions [1]. 25 × 2⁸ = 25 × 256 = 6400 [1]. [5] Examiner insight: Write the number of divisions before the final multiplication; this makes each step of your reasoning easy to follow.

6. A plasmid carrying the resistance gene is copied [1]. The copy passes from one bacterium to another by conjugation [1]. The recipient, which may be a different species, now has the gene [1]. It is horizontal because the gene passes between existing cells, not from parent to offspring [1]. [4] Examiner insight: Name conjugation and contrast with parent-to-offspring passage; a description of binary fission does not explain the movement between species.

7. (a) Codon 3 becomes CCG [1], which also codes for Pro, so the sequence is Met - Glu - Pro - Phe - Arg - Thr with no change [1]. (b) Codon 2 becomes UAA [1], a stop codon, so the chain is Met only [1]. (c) Reading in threes after deleting base 4 gives AUG AAC CAU UUC GCA CUU [1]. The sequence is Met - Asn - His - Phe - Ala - Leu, so Glu, Pro, Arg and Thr are replaced by Asn, His, Ala and Leu; Phe is unchanged because UUU and UUC both code for it [1]. [6] Examiner insight: Show the regrouped codons; naming the effect (no change, early stop or all later amino acids altered) is also expected.

8. A mutagen is a physical or chemical agent that increases the frequency of mutations [1]. Spontaneous mutations arise during DNA replication [1]. The genetic code is degenerate, so the new codon may code for the same amino acid [1]. [3] Examiner insight: Do not say mutagens cause mutations that would never otherwise occur; they increase how often they occur.

9. (a) Any two from: benign grows slower; benign usually encapsulated and malignant invades surrounding tissue; benign does not spread, malignant spreads to form secondary tumours [1] [1]. (b) The mutation produces an oncogene [1] that stimulates cells to divide too quickly, forming a mass of cells [1]. (c) The mutation inactivates the gene [1], so division is no longer slowed and the rate of division increases [1]. [6] Examiner insight: Name the gene type and its normal role; “the gene mutates and cancer forms” is too general.

10. (a) Incidence rises as sun exposure increases [1], from 8.2 to 26.9 per 100 000, a positive correlation [1]. (b) 26.9 / 8.2 [1] = 3.3 times (3.28) [1]. (c) The rise supports a link [1], but correlation alone does not prove cause, and other factors such as skin type, age or sunburn history may differ between groups [1]. A fuller evaluation needs sample sizes, how exposure was measured and a known mechanism, such as ultraviolet light damaging DNA [1]. [7] Examiner insight: Evaluation needs at least one limitation and one point in support; saying only “yes, it shows sunlight causes cancer” claims more than the data allow.

11. (a) Drug X acts in S phase [1], so DNA cannot replicate and the cell cannot complete the cycle [1]. Drug Y acts in mitosis [1], so chromatids cannot be separated and cells cannot divide [1]. (b) Hair follicle cells divide often [1], so they are also affected by the drug and hair growth stops [1]. [6] Examiner insight: Pair each drug with its phase and with a consequence; a list of side effects without the link to dividing cells misses the reasoning.

12. (a) Untreated: 29 / 242 × 100 = 12.0% [1]. Treated: 52 / 260 × 100 = 20.0% [1]. (b) Cut the root tip and warm it in hydrochloric acid [1]. Add a stain that binds chromosomes [1], place under a coverslip and squash into a single layer of cells [1]. (c) Count more fields or cells from several root tips and keep the total number similar [1]. [6] Examiner insight: Give the formula or the working with the percentage; stating the order of steps (acid, stain, squash) earns more than listing equipment.

Where marks are usually lost

• Writing “DNA replicates in mitosis” instead of S phase.
• Saying chromosomes separate in metaphase when they separate in anaphase.
• Using “chromosome” and “chromatid” interchangeably.
• Omitting the centromere when describing spindle fibres.
• Saying all mutations change the protein.
• Treating a deletion as a substitution and ignoring the shift in reading frame.
• Concluding from correlation alone that a risk factor causes cancer.
• Dividing by dividing cells only when finding the mitotic index.

Next steps

• Revise: revision notes and study guide
• Course: OxfordAQA A-level Biology hub and checklist
• Check your level with the free diagnostics
• Book a free trial class: trial

Official syllabus

Source: OxfordAQA, International AS and A-level Biology (9610), Version 5.1, International AS exams May/June 2017 onwards and International A-level exams May/June 2018 onwards, sections 3.2.10, 3.2.11 and Required practical 4.