Sexual and asexual reproduction — AQA GCSE Combined Science
Test yourself on Sexual and asexual reproduction with AQA GCSE practice questions.
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Sexual and asexual reproduction explained
Mitosis and meiosis both copy DNA before dividing, but they differ in outcome.
Read the full explanation
In mitosis one parent cell divides once to give two daughter cells that are genetically identical to each other and to the parent, so chromosome number is unchanged; this suits growth, repair and asexual reproduction. In meiosis a cell divides twice to give four gametes. Because pairs of chromosomes separate and genetic information is mixed, each gamete is genetically different from the parent and from the other gametes. Fertilisation then restores the full number of chromosomes, so sexual reproduction produces non-identical offspring.
Sexual reproduction involves the joining (fusion) of male and female gametes:
Sexual reproduction is the production of offspring by the fusion of two gametes, one male and one female. Gametes are sex cells produced by meiosis, so each carries half the normal chromosome number. At fertilisation the gamete nuclei join, restoring the full chromosome number in the zygote. Because each parent contributes one set of chromosomes, the offspring inherits a mixture of alleles and is genetically different from either parent and from its siblings. This variation is the key advantage of sexual reproduction. For example, in humans a sperm nucleus (23 chromosomes) fuses with an egg nucleus (23 chromosomes) to form a zygote with 46 chromosomes. The process requires two parents, or at least two gametes, and is slower than asexual reproduction but generates genetic variation that can help a population survive environmental change.
sperm and egg cells in animals
In animals the male gamete is the sperm cell and the female gamete is the egg cell, also called the ovum. Both are produced by meiosis, so each nucleus contains half the normal chromosome number: in humans, 23 chromosomes. The sperm is adapted for movement, with a tail to swim and many mitochondria to release energy for swimming, and its acrosome contains enzymes to digest a path into the egg. The egg is larger and non-motile, with food reserves in the cytoplasm to support the early embryo and a jelly coat that changes after fertilisation to block further sperm. At fertilisation the sperm nucleus fuses with the egg nucleus, forming a zygote with the full 46 chromosomes. The zygote then divides by mitosis to develop into an embryo.
pollen and egg cells in flowering plants.
Flowering plants reproduce sexually using specialised gametes: pollen grains (male) and egg cells, also called ova (female). Pollen is made in the anther of the stamen; each pollen grain contains a male nucleus and is carried by wind or insects to the stigma. The egg cell sits inside the ovule in the ovary. When a pollen tube grows down the style, the male nucleus fuses with the egg nucleus in fertilisation, forming a zygote that develops into an embryo inside a seed. The ovule becomes the seed and the ovary becomes the fruit. Both gametes are haploid, so fusion restores the diploid chromosome number.
In sexual reproduction there is mixing of genetic information which leads to variety in the offspring. The formation of gametes involves meiosis.
Sexual reproduction combines genetic material from two parents, so each offspring receives a mixture of alleles and is genetically different from its parents and siblings. Gametes are formed by meiosis, a type of cell division that halves the chromosome number. In meiosis, copies of the genetic information are made, and then the cell divides twice to form four gametes, each with a single set of chromosomes. All four gametes are genetically different from each other. For example, human sperm and egg cells each contain 23 chromosomes. When they fuse during fertilisation, the full number of 46 is restored. This mixing of genetic information leads to variety in the offspring.
Asexual reproduction involves only one parent and no fusion of gametes. There is no mixing of genetic information. This leads to genetically identical offspring (clones). Only mitosis is involved.
Asexual reproduction produces offspring from a single parent, so no gametes fuse and no genetic material is exchanged. Because the parent cell divides by mitosis, each daughter cell receives an exact copy of the parent's chromosomes. The offspring are therefore genetically identical clones of the parent. A familiar example is a strawberry plant sending out runners: each new plantlet is genetically the same as the parent plant. Potato tubers sprouting are another example. This contrasts with sexual reproduction, where two parents contribute gametes and meiosis creates genetic variation. Understanding this distinction lets you explain why asexual populations may struggle if the environment changes, since all individuals share the same alleles.
Your focus
- State that mitosis produces two genetically identical cells while meiosis produces four non-identical gametes.
- Describe how the two divisions of meiosis halve the chromosome number and reshuffle alleles.
- Explain why identical cells are useful for growth and asexual reproduction, while non-identical gametes are important for sexual reproduction.
Show all 18 objectives
- State that sexual reproduction involves the fusion of male and female gametes.
- Describe how fertilisation restores the full chromosome number in the zygote.
- Explain why sexual reproduction produces offspring that are genetically different from the parents.
- Identify the sperm and egg as the male and female gametes in animals.
- Describe how the structure of sperm and egg cells is adapted to their functions.
- Explain how the fusion of sperm and egg nuclei produces a zygote with the full chromosome number.
- Identify pollen grains and egg cells as the male and female gametes in flowering plants.
- Describe the pathway from pollen landing on the stigma to fertilisation in the ovule.
- Explain how the ovule and ovary develop into the seed and fruit after fertilisation.
- Describe how meiosis forms gametes with half the normal number of chromosomes.
- Explain how mixing of genetic information in sexual reproduction leads to variety in offspring.
- Compare the outcomes of meiosis and mitosis in terms of cell number and genetic variation.
- State that asexual reproduction involves one parent and no fusion of gametes.
- Describe how mitosis produces genetically identical offspring called clones.
- Explain why asexual offspring show no genetic variation and give a named example.
Sexual and asexual reproduction exam tips
Marking Points
- Mitosis involves one division and produces two daughter cells that are genetically identical to the parent cell, with the same chromosome number.
- Meiosis involves two divisions and produces four gametes, each with half the chromosome number of the parent cell.
- In meiosis, pairs of chromosomes separate and genetic information is mixed, so the resulting cells are non-identical.
- Mitosis supports growth, repair of tissues and asexual reproduction, where identical offspring are advantageous.
- Meiosis produces gametes for sexual reproduction, and the genetic variation it generates gives offspring a better chance of surviving changed conditions.
- Gametes are sex cells produced by meiosis and carry half the chromosome number of a body cell.
- Fusion means the male and female gamete nuclei join to form a single cell, the zygote.
- Fertilisation restores the full, diploid chromosome number in the zygote.
- Each parent contributes one set of chromosomes, so the offspring receives a mixture of alleles.
- The offspring are genetically different from each other and from their parents, giving variation.
- Sexual reproduction requires two gametes, so it usually involves two parents.
- The sperm is the male gamete and the egg (ovum) is the female gamete in animals.
- Both gametes are produced by meiosis and carry half the normal chromosome number, 23 in humans.
- The sperm has a tail and many mitochondria for swimming and releasing energy.
- The egg is larger, non-motile and contains food reserves for the early embryo.
- Fertilisation is the fusion of the sperm nucleus and egg nucleus to form a zygote.
- The zygote has the full chromosome number and divides by mitosis to form the embryo.
- Pollen grains are the male gametes and are produced in the anther of the stamen.
- Egg cells (ova) are the female gametes and are found inside the ovule within the ovary.
- Pollen is transferred to the stigma by wind or insects, then a pollen tube grows down the style to the ovule.
- Fertilisation is the fusion of the male nucleus from the pollen grain with the female nucleus of the egg cell.
- After fertilisation the ovule becomes the seed and the ovary develops into the fruit.
- Both gametes are haploid, so fertilisation restores the diploid number in the zygote.
- Sexual reproduction involves the fusion of male and female gametes, mixing genetic information from two parents.
- Meiosis halves the chromosome number, producing gametes with a single set of chromosomes.
- In meiosis, copies of the genetic information are made before the cell divides twice.
- Meiosis produces four gametes that are all genetically different from each other.
- Random fertilisation of gametes restores the full number of chromosomes and adds further genetic variation.
- The resulting offspring show variety and are genetically different from each other and from their parents.
- Asexual reproduction involves one parent only, with no fusion of gametes.
- No mixing of genetic information occurs, so offspring are genetically identical clones of the parent.
- Only mitosis is involved, producing genetically identical daughter cells.
- Examples include runners in strawberry plants and tubers in potatoes.
- Because offspring are clones, they share the same alleles and may be equally vulnerable to a change in environment or a new disease.
Examiner Tips
- 💡State the number of divisions and the number and type of cells produced for each process before explaining the genetic outcome.
- 💡Use the terms diploid and haploid to compare chromosome numbers in parent cells, gametes and daughter cells.
- 💡When comparing the two processes, structure your answer as direct pairs, such as one division versus two divisions, rather than describing each process separately.
- 💡Use the word fusion or fertilisation when describing the joining of gamete nuclei, and name the product as a zygote.
- 💡State chromosome numbers explicitly, for example sperm 23 and egg 23 joining to give a zygote with 46, to show the halving and restoring idea.
- 💡Link sexual reproduction to variation in a final sentence, because questions often ask why sexual reproduction produces variation.
- 💡Name both gametes and give their chromosome numbers to show they are haploid.
- 💡When asked about adaptation, link each sperm or egg feature to its function, such as tail for swimming or food store for the embryo.
- 💡Describe fertilisation as the fusion of nuclei, not just the joining of whole cells, to gain credit for the genetic point.
- 💡Label a flower diagram with anther, stigma, style, ovary and ovule, then state the job of each part.
- 💡Use the phrase 'fusion of the male nucleus and egg nucleus' rather than vague wording such as 'they join'.
- 💡Link each structure to its fate after fertilisation: ovule to seed, ovary to fruit.
- 💡Compare meiosis and mitosis in a table: number of divisions, number of cells produced, and genetic variation.
- 💡State clearly that meiosis halves the chromosome number, and fertilisation restores it.
- 💡Explain variety by referring to the mixing of genetic information from two parents and the formation of non-identical gametes.
- 💡Link each clause of the definition to a named example, such as strawberry runners, to show understanding.
- 💡Use the phrase genetically identical clones rather than just identical, to match the specification wording.
- 💡When comparing with sexual reproduction, mention both variation and the number of parents to gain comparison credit.
Common Mistakes
- Saying meiosis produces two cells: correct this by stating that meiosis involves two divisions and produces four gametes.
- Saying mitosis produces gametes: correct this by stating that mitosis produces identical body cells for growth and repair, while meiosis produces gametes.
- Believing meiosis keeps the chromosome number the same: correct this by stating that meiosis halves the chromosome number.
- Saying gametes are produced by mitosis; correction: gametes are produced by meiosis, which halves the chromosome number.
- Writing that the gametes fuse to make a body cell directly; correction: the fused cell is a zygote, which divides by mitosis to form the embryo.
- Claiming offspring are identical to parents; correction: because two sets of alleles combine, offspring show genetic variation.
- Calling the egg a cell with a full set of chromosomes; correction: the egg nucleus is haploid, carrying 23 chromosomes in humans.
- Saying the sperm cell has no cytoplasm or mitochondria; correction: it has a small amount of cytoplasm and many mitochondria to supply energy for swimming.
- Confusing fertilisation with implantation; correction: fertilisation is the fusion of gamete nuclei, while implantation is the embedding of the embryo in the uterus lining.
- Saying pollen is the male sex cell and stopping there; correct by naming the male nucleus inside the pollen grain as the gamete that fuses.
- Confusing the ovary with the ovule; correct by stating the ovule contains the egg cell and becomes the seed, while the ovary becomes the fruit.
- Thinking pollen travels down the pollen tube; correct by stating the pollen tube grows down the style carrying the male nucleus to the egg cell.
- Saying meiosis produces two identical cells; correct by stating it produces four genetically different cells.
- Confusing meiosis with mitosis; correct by noting mitosis produces two genetically identical cells for growth and repair.
- Stating that gametes have the full number of chromosomes; correct by stating gametes have half the number so that fertilisation restores the full set.
- Saying asexual reproduction involves two parents but no gametes: correct this by stating that only one parent is involved.
- Confusing mitosis with meiosis in asexual reproduction: correct this by stating that only mitosis occurs, producing identical cells.
- Claiming offspring are similar but not identical: correct this by stating they are genetically identical clones, except for rare mutations.