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Exam questions · Biology · Inheritance

Meiosis, Haploid and Diploid

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

    State the number of chromosomes in a human body cell and in a human egg cell.

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    Model answer

    46 in a body cell, and 23 in an egg cell.

    Mark scheme

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

    Give the meaning of the terms haploid and diploid.

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    Model answer

    Haploid means having one set of chromosomes. Diploid means having two sets of chromosomes.

    Mark scheme

    • Haploid: one set — 1 mark
    • Diploid: two sets — 1 mark
  3. 3 Calculate [2 marks]

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

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    Model answer

    48 ÷ 2 = 24 chromosomes.

    Mark scheme

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

    Explain why gametes are made by meiosis, and not by mitosis.

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    Model answer

    Meiosis halves the chromosome number, so that the gametes are haploid. When they fuse, the zygote is diploid. If mitosis were used, the gametes would be diploid, and the number of chromosomes would double with each generation. Meiosis also makes the gametes genetically different.

    Mark scheme

    • Meiosis gives haploid gametes — 1 mark
    • Fertilisation maintains the diploid number — 1 mark
    • Mitosis would double the number each generation — 1 mark
  5. 5 Describe [4 marks]

    Describe the differences between mitosis and meiosis.

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    Model answer

    Mitosis makes two cells, but meiosis makes four. The cells made by mitosis are diploid, but those made by meiosis are haploid. The cells from mitosis are genetically identical, but those from meiosis are genetically different. Mitosis is used for growth and repair, but meiosis is used to make gametes.

    Mark scheme

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

    Explain how meiosis and fertilisation maintain the diploid number, and how they are sources of genetic variation.

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    Model answer

    Meiosis halves the number of chromosomes, so each gamete is haploid, with one set of chromosomes. At fertilisation a male and a female gamete fuse to make a zygote, which is diploid, with two sets of chromosomes. This maintains the diploid number in every generation. In meiosis the pairs of chromosomes are shared out at random, so each gamete has a different mixture of the chromosomes that came from the parents' own mother and father. A person can make millions of different gametes. Any one of the gametes can fertilise any egg, so the offspring have a different combination of genes from their parents and from each other.

    Mark scheme

    • Meiosis halves the number, so gametes are haploid — 1 mark
    • Fertilisation makes a diploid zygote — 1 mark
    • So the diploid number is maintained — 1 mark
    • Chromosomes shared out at random — 1 mark
    • Millions of different gametes — 1 mark
    • Fertilisation is random, so the offspring are different — 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.

  2. 2

    How many chromosomes does a human sperm cell have?

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

    Gametes are haploid, so they have 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

    Four.

  4. 4

    What is a zygote?

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

    The diploid cell formed when two gametes fuse.

  5. 5

    What does haploid mean?

    1. AHaving two sets of chromosomes
    2. BHaving one set of chromosomes
    3. CHaving no chromosomes
    4. DHaving four sets of chromosomes
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    B: Having one set of chromosomes

    Having one set of chromosomes.

  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.

  7. 7

    A body cell has 16 chromosomes. How many are in a gamete?

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

    \(16 \div 2 = 8\).

  8. 8

    Why do brothers and sisters look different?

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

    Each gamete has a different mixture of chromosomes, and fertilisation is random.

  9. 9

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

    1. AThey come from one 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

    They come from one fertilised egg that splits in two.