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Exam questions · Biology · Reproduction, Meiosis and Variation

Meiosis and Gametes

  • 6 exam questions
  • 19 marks
  • 9 quick checks
  1. 1 State [2 marks]

    State the number of chromosomes in (a) a human body cell and (b) a human sperm cell.

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    Model answer

    (a) 46. (b) 23.

    Mark scheme

    • 46 — 1 mark
    • 23 — 1 mark
  2. 2 State [2 marks]

    Name the type of cell division that produces gametes, and give the number of cells that one cell produces.

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    Model answer

    Meiosis. Four cells.

    Mark scheme

    • Meiosis — 1 mark
    • Four — 1 mark
  3. 3 Calculate [2 marks]

    A potato plant has 48 chromosomes in a body cell. Calculate the number of chromosomes in a pollen grain.

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    Model answer

    Gametes have half the number of chromosomes, so 48 ÷ 2 = 24.

    Mark scheme

    • Halves the number — 1 mark
    • 24 — 1 mark
  4. 4 Explain [3 marks]

    Explain why gametes have half the number of chromosomes of a body cell.

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    Model answer

    When a male and a female gamete fuse at fertilisation, their chromosomes are combined. If the gametes had a full set each, the zygote would have double the number. Halving the number in the gametes means that the zygote has the normal diploid number.

    Mark scheme

    • Fertilisation combines the chromosomes of two gametes — 1 mark
    • A full set each would double the number — 1 mark
    • So the zygote has the normal number — 1 mark
  5. 5 Compare [4 marks]

    Compare meiosis and mitosis.

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    Model answer

    Mitosis produces two cells, whereas meiosis produces four. The cells from mitosis are genetically identical to the parent and diploid, but the cells from meiosis are genetically different from each other and haploid, with half the number of chromosomes. Mitosis is used for growth and repair, and meiosis is used to make gametes.

    Mark scheme

    • Two cells and four cells — 1 mark
    • Identical and different — 1 mark
    • Diploid and haploid — 1 mark
    • Growth and repair, and gametes — 1 mark
  6. 6 Explain [6 marks]

    Explain how meiosis and fertilisation lead to genetic variation in the offspring of two parents.

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    Model answer

    In meiosis, the pairs of chromosomes are shared out at random, so each gamete receives a different mixture of the maternal and paternal chromosomes. This means that the four cells produced are all genetically different. A person can make millions of different gametes, since there are 23 pairs of chromosomes. At fertilisation, any one of the many different sperm can fuse with any one of the eggs, and this is also random. So the offspring have a unique combination of genes, which makes them different from their parents and from their brothers and sisters.

    Mark scheme

    • Pairs of chromosomes shared out at random — 1 mark
    • Each gamete has a different mixture — 1 mark
    • Gametes are genetically different — 1 mark
    • Millions of possible combinations — 1 mark
    • Fertilisation is random — 1 mark
    • Offspring are unique — 1 mark

Quick check

  1. 1

    Which cells are made by meiosis?

    1. ASkin cells
    2. BMuscle cells
    3. CGametes
    4. DRed blood cells
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    C: Gametes

    Meiosis makes gametes, which are the sperm and egg cells.

  2. 2

    How many chromosomes does a human egg cell have?

    1. A46
    2. B23
    3. C92
    4. D2
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    B: 23

    Gametes are haploid, so a human egg has 23 chromosomes.

  3. 3

    How many cells are made when one cell divides by meiosis?

    1. A1
    2. B2
    3. C3
    4. D4
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    D: 4

    Meiosis produces four cells.

  4. 4

    What is a zygote?

    1. AThe cell formed at fertilisation
    2. BA type of sperm cell
    3. CA cell made by mitosis in a muscle
    4. DA cell with half the chromosomes
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    A: The cell formed at fertilisation

    A zygote is the cell formed when a sperm and an egg fuse, and it has the full diploid number.

  5. 5

    Which is true of the cells made by meiosis?

    1. AThey are all identical
    2. BThey are haploid and genetically different
    3. CThey are diploid
    4. DThey are made in the heart
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    B: They are haploid and genetically different

    The four cells are haploid, and they are genetically different from each other.

  6. 6

    Which type of cell division is used for growth and repair?

    1. AMeiosis
    2. BFertilisation
    3. CMitosis
    4. DDifferentiation
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    C: Mitosis

    Mitosis makes genetically identical cells for growth and repair.

  7. 7

    A cell has 16 chromosomes. How many chromosomes are in its gametes?

    1. A8
    2. B16
    3. C32
    4. D4
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    A: 8

    Gametes have half the chromosomes of a body cell: \(16 \div 2 = 8\).

  8. 8

    Why do brothers and sisters from the same parents look different?

    1. AThey have different parents
    2. BThey are made by mitosis
    3. CThey have a different number of chromosomes
    4. DEach gamete has a different mix of genes
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    D: Each gamete has a different mix of genes

    Each gamete has a different, random mix of chromosomes, and fertilisation is also random, so each child has a different combination.

  9. 9

    Identical twins have the same genes. Which statement explains this?

    1. AThey come from the same sperm and two eggs
    2. BThey come from one fertilised egg that splits
    3. CThey are made by meiosis
    4. DThey have different parents
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    B: They come from one fertilised egg that splits

    Identical twins come from one fertilised egg that splits in two, so both have the same genes.