Mitosis and Meiosis: How Cells Divide — Answers
Answer sheet with model answers and success criteria for the Year 10 cells & classification worksheet.
Success TutoringWorksheetsAnswer sheetYear 10 · Science · Cells & ClassificationMitosis and Meiosis: How Cells Divide — Answers
Part A: The cell cycle and mitosis
The cell cycle has two main parts. During interphase the cell grows, makes new organelles and copies its DNA. During mitosis the nucleus divides, then the cytoplasm splits (cytokinesis) to make two genetically identical daughter cells.
Mitosis has four stages: prophase, metaphase, anaphase and telophase.
- Prophase
- Metaphase
- Anaphase
- Telophase
- Sister chromatids are pulled apart to opposite ends of the cell
- Chromosomes condense and become visible; the nuclear membrane breaks down
- New nuclear membranes form around each set of chromosomes
- Chromosomes line up across the middle of the cell
Answer: Prophase → Chromosomes condense and become visible; the nuclear membrane breaks down; Metaphase → Chromosomes line up across the middle of the cell; Anaphase → Sister chromatids are pulled apart to opposite ends of the cell; Telophase → New nuclear membranes form around each set of chromosomes
Answer: The DNA is copied (replicated), so each chromosome becomes two identical sister chromatids. This means each new cell can receive a full, identical set of chromosomes.
Answer: Any two of: growth; repairing damaged tissue (such as healing a cut); replacing worn-out cells (such as skin or red blood cells); asexual reproduction in some organisms.
Answer: True
Each daughter cell receives an exact copy of the parent cell's chromosomes.
Answer: 32
- 5 days = 5 divisions
- 1 × 2⁵ = 32 cells
Part B: Meiosis
Meiosis makes gametes (sex cells). It involves two divisions and produces four cells, each with half the number of chromosomes of a body cell. Body cells are diploid (two sets of chromosomes); gametes are haploid (one set).
During meiosis, chromosome pairs are shuffled and swap sections, so every gamete is genetically different. This is a source of variation.
- AIn all body cells
- BIn the skin
- CIn the ovaries and testes
- DIn the bone marrow
Answer: In the ovaries and testes
Meiosis produces gametes (eggs and sperm), so it happens only in the reproductive organs.
Answer: 23; 46
- Gametes are haploid: 46 ÷ 2 = 23
- Zygote: 23 + 23 = 46
Answer: 39
- 78 ÷ 2 = 39
Answer: 8
- Body cells are diploid: 4 × 2 = 8
Answer: So that when two gametes fuse at fertilisation, the zygote has the normal diploid number. If gametes were diploid, the chromosome number would double in every generation.
Answer: Any two: mitosis has one division, meiosis has two; mitosis makes 2 cells, meiosis makes 4; mitosis cells are diploid, meiosis cells are haploid; mitosis cells are genetically identical, meiosis cells are genetically different; mitosis is for growth and repair, meiosis makes gametes.
Part C: Investigating mitosis
The mitotic index is the percentage of cells in a sample that are dividing. A higher mitotic index means faster cell division.
Answer: 5%
- mitotic index = dividing cells ÷ total cells × 100
- 20 ÷ 400 × 100 = 5%
Answer: 1 hour
- About 5% of cells are in mitosis, so mitosis takes about 5% of the cycle
- 0.05 × 20 = 1 hour
Answer: The root tip is where the root grows, so cells there are dividing rapidly by mitosis.
Part D: Explain
Model answer: Normally the cell cycle is controlled by genes, so cells divide only when new cells are needed and stop when they are not. A mutation in these control genes can cause a cell to divide by mitosis again and again without stopping. The copies also divide uncontrollably, forming a lump of abnormal cells called a tumour. If cells break away and spread through the blood, they can form new tumours elsewhere. Treatments such as chemotherapy and radiotherapy damage the DNA of cells or stop mitosis, which affects rapidly dividing cancer cells most. However, some healthy cells also divide rapidly, such as hair follicle cells, cells lining the gut and bone marrow cells, so they are damaged too, causing side effects such as hair loss, nausea and tiredness.
Success criteria:
- Normal cell division is controlled by genes
- A mutation causes uncontrolled mitosis, forming a tumour
- Treatments target rapidly dividing cells by damaging DNA or stopping mitosis
- Healthy rapidly dividing cells (such as hair follicles) are also affected
Marking tips
- Give credit for correct method even when the final answer slips — the working shows where the thinking went right.
- For open-ended tasks, use the success criteria as a checklist rather than looking for one "right" answer.
- Celebrate what went well first, then pick one thing to work on next.
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