AQA A-level Biology: The Cell Cycle, Mitosis and Required Practical 2 (7402) – 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 are aligned to section 3.2.2, All cells arise from other cells, in the AQA AS and A-level Biology specification (A-level 7402), for first teaching 2015, exams June 2016 onwards. The section is AS content and includes required practical 2. Questions 6 to 9 use the practical and the mathematical skills MS 0.3 (percentages and ratios) and MS 1.8 (magnification). Every answer shows the working and the marking points.

Related: The cell cycle, mitosis and required practical 2 study guide and revision notes. Course hub: AQA A-level Biology.

How should you use these questions?

Write full answers under timed conditions (roughly one minute per mark), then mark them against the answers. AQA mark schemes reward precise terms: chromatids, centromeres, spindle fibres, interphase.

Questions

1. State the stage of the cell cycle in which DNA replication occurs, and explain why it must occur before mitosis. [2]

2. Describe the behaviour of chromosomes during prophase and metaphase of mitosis. [4]

3. In anaphase, the chromatids appear V-shaped as they move. Explain this appearance. [2]

4. Explain why the two daughter cells produced by mitosis are genetically identical to each other and to the parent cell. [2]

5. A drug used in cancer treatment prevents spindle fibres from forming.

(a) Explain how this drug slows the growth of a tumour. [2] (b) Suggest why patients given this drug may lose hair. [2]

6. A student prepared a squash of a garlic root tip.

(a) Explain why the student used the tip of the root. [1] (b) Give the purpose of placing the root tip in warm hydrochloric acid. [1] (c) Explain why the student pressed the cover slip down firmly, without twisting it. [2]

7. The student counted cells in one field of view.

Stage	Number of cells
Interphase	112
Prophase	21
Metaphase	9
Anaphase	4
Telophase	4

(a) Calculate the mitotic index. [2] (b) The cell cycle in this tissue takes 18 hours. Calculate how long, in minutes, a cell spends in metaphase. [2] (c) Suggest two ways the student could make the mitotic index more representative of the whole root tip. [2]

8. A cell in prophase measures 36 mm on a photomicrograph taken at a magnification of x 1500. Calculate its actual length in micrometres. [2]

9. Two root tips were treated with different concentrations of a chemical. Tip A gave a mitotic index of 0.21; tip B gave 0.09. A student concludes the chemical at the concentration used for B inhibits cell division. Give two pieces of information you would need before accepting this conclusion. [2]

10. Describe binary fission in a bacterium. [3]

11. Explain why viruses are not described as undergoing cell division, and describe how new virus particles are produced. [3]

12. Not all cells in a multicellular organism retain the ability to divide. Give the term for the repeating sequence of events shown by cells that do, and name its two main phases. [2]

Answers

1. Interphase [1]. So that each chromosome is made of two identical sister chromatids, one of which passes to each daughter cell [1].

2. Prophase: chromosomes condense / shorten and thicken [1]; each is seen as two chromatids joined at a centromere, and the nuclear envelope breaks down [1]. Metaphase: chromosomes line up at the equator of the cell [1]; spindle fibres attach to the centromeres [1].

3. Spindle fibres are attached to the centromeres and shorten, pulling the centromere first [1], so the arms of each chromatid trail behind it [1].

4. DNA is replicated (semi-conservatively) before division, so the sister chromatids are identical copies [1]. Sister chromatids are separated so that each daughter cell receives one copy of every chromosome [1].

5. (a) Chromatids cannot be separated, so mitosis cannot be completed [1]; the rate of cell division in the tumour falls, so it grows more slowly [1]. (b) Hair follicle cells also divide rapidly by mitosis [1], so the drug stops them dividing too and hair is not replaced [1].

6. (a) The tip contains the meristem, where cells are dividing by mitosis [1]. (b) To separate the cells (break down the material holding them together) so they can be spread, and/or to stop mitosis [1]. (c) To spread the cells into a single layer so light passes through and chromosomes can be seen [1]; twisting would break the chromosomes or tear the cells / damage the slide [1].

7. (a) Cells in mitosis = 21 + 9 + 4 + 4 = 38 [1]; total = 112 + 38 = 150; mitotic index = 38 / 150 = 0.25 (0.253) [1]. (b) Proportion in metaphase = 9 / 150 = 0.06 [1]; 0.06 x 18 hours = 1.08 hours = 64.8 minutes (about 65 minutes) [1]. (c) Any two [1 each]: count several fields of view; use several root tips (or slides); count a larger number of cells; choose fields of view at random.

8. Actual size = 36 mm / 1500 = 0.024 mm [1] = 24 micrometres [1].

9. Any two [1 each]: the mitotic index for an untreated (control) tip; the number of cells / fields of view counted; whether repeats gave similar results (and their spread); whether the tips came from the same plant, of the same age, and were taken from the same region of the root.

10. 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 a variable number of plasmids [1].

11. Viruses are non-living / are not cells [1]. The virus injects its nucleic acid into a host cell [1]; the host cell replicates the viral nucleic acid and makes new virus particles, which are released [1].

12. The cell cycle [1]; interphase and mitosis (with cytokinesis) [1].

Where marks are usually lost

• Writing “chromosomes separate” in anaphase instead of “sister chromatids separate”.
• Leaving out the centromere when describing spindle attachment.
• Rounding too early in time calculations, or giving hours when minutes are asked for.
• Forgetting to convert millimetres to micrometres (multiply by 1000).
• Saying the acid “kills” the cells without explaining why that helps.

Frequently asked questions

Is cytokinesis part of mitosis? The specification treats mitosis as nuclear division and says cytokinesis usually follows. When asked to recognise stages of the cell cycle, telophase is listed “including cytokinesis”.

What counts as “in mitosis” for the mitotic index? Cells in prophase, metaphase, anaphase and telophase. Interphase cells are not dividing.

How do I find the time spent in one stage? Multiply the fraction of cells in that stage by the length of the whole cell cycle.

Official syllabus

AQA AS and A-level Biology (7401/7402) specification, Version 1.5, section 3.2.2 All cells arise from other cells, including required practical 2.