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AQA A-Level Biology (Paper 1) Smart practice A mixed round aimed at your weak spots
Unit 1
Biological molecules
Monomers and polymers; carbohydrates
Monomers, polymers and carbohydrates
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Lipids
Lipids
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Proteins
General properties of proteins
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Many proteins are enzymes
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Nucleic acids are important information-carrying molecules
Structure of DNA and RNA
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DNA replication
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ATP
ATP
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Water; inorganic ions
Water and inorganic ions
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Unit 2
Cells
Cell structure
Structure of eukaryotic cells
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Structure of prokaryotic cells and of viruses
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Methods of studying cells
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All cells arise from other cells
All cells arise from other cells
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Transport across cell membranes
Membrane structure, diffusion and osmosis
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Active transport and co-transport
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Cell recognition and the immune system
Antigens, phagocytosis and T lymphocytes
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B lymphocytes, antibodies and vaccination
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HIV, monoclonal antibodies and the ELISA test
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Unit 3
Organisms exchange substances with their environment
Surface area to volume ratio
Surface area to volume ratio
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Gas exchange
Adaptations of gas exchange surfaces
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Human gas exchange, ventilation and lung disease
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Digestion and absorption
Digestion and absorption
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Mass transport in animals
Haemoglobin and the transport of oxygen
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The heart, cardiac cycle and cardiovascular disease
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Blood vessels and tissue fluid
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Mass transport in plants
Xylem and the cohesion-tension theory
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Phloem and translocation by mass flow
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Unit 4
Genetic information, variation and relationships between organisms
DNA, genes and chromosomes
DNA, genes and chromosomes
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DNA and protein synthesis
Genome, proteome, transcription and splicing
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Translation: ribosomes, tRNA and ATP
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Genetic diversity can arise as a result of mutation or during meiosis
Gene mutations and chromosome non-disjunction
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Meiosis and genetic variation
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Genetic diversity and adaptation
Genetic diversity and adaptation
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Species and taxonomy
Species and taxonomy
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Biodiversity within a community
Biodiversity within a community
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Investigating diversity
Investigating diversity
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Meiosis and genetic variation

Practise 18 exam-style questions on Meiosis and genetic variation for AQA A-Level Biology (Paper 1). Write your answer as you would in the exam and get it marked in seconds against the mark scheme, point by point, with the Study Helper on hand if you get stuck.

  • 18 questions
  • 1–8 marks each
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18 questions, marked as you go

Sample questions with model answers

Here are 4 of the questions in this topic, each with a model answer, an explanation of why it earns the marks and the mark scheme an examiner would use.

Question 1

2 marks

Human body cells contain 23 pairs of homologous chromosomes. One chromosome of each pair came from the person's mother and the other from the person's father.

Ignoring crossing over, calculate the probability that a gamete produced by a person contains only chromosomes that came from that person's mother.

Give your answer in standard form to 2 significant figures.

Model answer

For each of the 23 pairs, the probability that the gamete receives the chromosome from the mother is 1/2, and the pairs segregate independently.
Probability = (1/2)²³ = 1 ÷ 8 388 608 = 1.19 × 10⁻⁷ = 1.2 × 10⁻⁷

Explanation

Because each homologous pair lines up independently in meiosis I, the chance of the maternal chromosome going into a gamete is 1/2 for each pair, and independent probabilities are multiplied. This is the same idea as the 2ⁿ combinations: the all-maternal gamete is just one of 2²³ equally likely combinations. A common error is to use 46 chromosomes instead of 23 pairs.

Mark scheme
  1. 1 mark

    Correct method, e.g. (1/2)²³ or 1 ÷ 2²³ (= 1 ÷ 8 388 608); or a correct final answer of 1.2 × 10⁻⁷ with no working

    A correct answer of 1.2 × 10⁻⁷ with no working scores 2 marks. Accept for 1 mark: 1.19 × 10⁻⁷ or 1.192 × 10⁻⁷ (not to 2 significant figures) OR 0.00000012 (not in standard form) OR 1/8 388 608. Reject 1/46, 1/23 and (1/2)⁴⁶ for any mark.

  2. 1 mark

    1.2 × 10⁻⁷

Question 2

3 marks

In honeybees, females develop from fertilised eggs and have 32 chromosomes in each body cell. Males develop from unfertilised eggs and have 16 chromosomes in each body cell. A female queen bee produces eggs by meiosis. A male produces sperm by a type of cell division that does not change the chromosome number, so all the sperm from one male are genetically identical.

Use your knowledge of meiosis to explain why a male could not produce sperm by normal meiosis.

A queen mated with one male. Ignoring crossing over and mutation, calculate the number of different combinations of chromosomes possible among her female offspring.

Model answer

A male's cells are haploid: they have only one chromosome of each type, so there are no homologous pairs that could pair up and separate in the first division of meiosis.

The queen has 16 homologous pairs, so her eggs can have 2¹⁶ = 65 536 combinations of chromosomes. All the sperm from the male are identical, so they add no further combinations. Number of combinations among female offspring = 65 536 × 1 = 65 536.

Explanation

Meiosis I depends on homologous chromosomes pairing and then separating; a haploid cell has nothing to pair with. The variation among the daughters therefore comes only from independent segregation in the queen (2ⁿ with n = 16). Using (2ⁿ)² assumes both parents produce varied gametes, which is not true here because the male's sperm are all identical.

Mark scheme
  1. 1 mark

    Egg cells: 2¹⁶ / 65 536 combinations; or a correct final answer of 65 536 with no working

    Points 1 and 2 are for the calculation: a correct answer of 65 536 (accept 2¹⁶) with no working scores 2 marks. Accept for 1 mark: 4.29 × 10⁹ / (2¹⁶)² (egg combinations correct but sperm wrongly treated as variable).

  2. 1 mark

    All sperm are identical (1 combination), so female offspring: 65 536 × 1 = 65 536

    Reject 2³² or 4.29 × 10⁹ for this point.

  3. 1 mark

    The male's cells are haploid / have only one set of chromosomes, so there are no homologous chromosomes / pairs to pair up and separate (in meiosis I)

    Accept 'no homologous pairs, so the chromosome number cannot be halved'. Accept 'meiosis would halve the number to 8, so the sperm would not have a complete set of chromosomes'. Insufficient: 'males are haploid' on its own.

Question 3

3 marks

The figure shows the life cycle of a fern. The cells of the large fern plant each contain 78 chromosomes. The cells of the small heart-shaped plant each contain 39 chromosomes.

Give the letter of the arrow that represents meiosis. Explain your answer.

Give the letters of all the arrows that represent mitosis.

Diagram of 5 boxes joined by 5 arrows. The boxes are: "Zygote" (top row, left), "Large fern plant" (top row, centre), "Spores" (second row, right), "Eggs and sperm" (third row, left of centre), "Small heart-shaped plant" (bottom row, right of centre). Arrows go from "Large fern plant" to "Spores", labelled P; from "Spores" to "Small heart-shaped plant", labelled Q; from "Small heart-shaped plant" to "Eggs and sperm", labelled R; from "Eggs and sperm" to "Zygote", labelled S; from "Zygote" to "Large fern plant", labelled T.

Model answer

Meiosis: P. The large fern plant is diploid (78 chromosomes), and the spores must be haploid (39) because they grow by mitosis into the small heart-shaped plant, which has 39 chromosomes. Meiosis is the division that halves the chromosome number.

Mitosis: Q, R and T.

Explanation

Find where the chromosome number halves: that is where meiosis occurs. In ferns this is when spores form, not when gametes form. The small haploid plant makes its eggs and sperm by mitosis (R), because its cells are already haploid; the spore grows into the small plant (Q) and the zygote grows into the large plant (T) by mitosis. S is fertilisation, which doubles the chromosome number. Many students assume gametes are always made by meiosis, as in animals.

Mark scheme
  1. 1 mark

    P

    Reject any other letter or more than one letter.

  2. 1 mark

    Chromosome number halves (from 78 to 39) / diploid to haploid between the large fern plant and the spores (which grow into the 39-chromosome plant)

    Accept 'spores have 39 chromosomes because they grow into the small plant by mitosis'. Insufficient: 'meiosis produces spores' with no reference to chromosome number.

  3. 1 mark

    Q, R and T

    All three letters needed and no others. Reject S (fertilisation).

Question 4

5 marks

Describe how the behaviour of chromosomes during meiosis halves the chromosome number. Explain why this halving is important in sexual reproduction.

Model answer

Before meiosis the DNA replicates, so each chromosome consists of two chromatids. In prophase I the homologous chromosomes pair up to form bivalents. In metaphase I these pairs line up on the equator, with the two chromosomes of each pair attached to spindle fibres from opposite poles. In anaphase I the homologous chromosomes separate, so one chromosome of each pair goes to each pole, and the cells formed at the end of meiosis I are haploid. In meiosis II the centromeres divide and the sister chromatids separate, producing four haploid cells.

This halving is important because at fertilisation two haploid gametes fuse, restoring the diploid number in the zygote. Without halving, the chromosome number would double in every generation.

Explanation

The halving happens in meiosis I, when homologous chromosomes separate; meiosis II separates sister chromatids and does not change the chromosome number. Answers often confuse the two divisions, or describe chromatids separating in anaphase I. Credit for importance needs the link to fertilisation keeping the number constant across generations.

Mark scheme
  1. 1 mark

    DNA replicates (in interphase) before meiosis, so each chromosome consists of two chromatids

    Max 5. Reject mitosis for meiosis.

  2. 1 mark

    Homologous chromosomes pair up / form bivalents (in prophase I)

    Accept 'chromosomes line up in their homologous pairs'.

  3. 1 mark

    (In metaphase I) homologous pairs line up on the equator, with each chromosome of a pair attached to spindle fibres from opposite poles

  4. 1 mark

    (In anaphase I) homologous chromosomes separate, one of each pair moving to each pole

    Reject chromatids separate in anaphase I.

  5. 1 mark

    So each cell after meiosis I has one chromosome from each pair / is haploid

    Accept 'chromosome number halved in the first division'.

  6. 1 mark

    (In meiosis II) centromeres divide and sister chromatids separate, giving four haploid cells

    Accept 'second division separates chromatids, like mitosis'.

  7. 1 mark

    At fertilisation two haploid gametes fuse to restore the diploid number

    Accept 'the zygote has the full number of chromosomes'.

  8. 1 mark

    So the chromosome number stays the same from one generation to the next / does not double each generation

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