Reproduction
SEAB syllabus topic 13: asexual and sexual reproduction, mitosis and meiosis, flowers and pollination, the human reproductive systems, the menstrual cycle, the foetus and HIV, with the why, the practicals, the traps and the exam checks.
Asexual reproduction needs one parent and gives genetically identical offspring, whereas sexual reproduction fuses the nuclei of male and female gametes and gives offspring that are genetically dissimilar.
In a flowering plant, pollination is followed by fertilisation in the ovule, and then the ovule becomes a seed and the ovary becomes a fruit.
In humans, the menstrual cycle, fertilisation, implantation and the placenta lead to the development of a foetus.
Reproduction links four ideas: mitosis and meiosis make the cells, flowers and the human reproductive systems make and bring together the gametes, fertilisation and implantation start a new individual, and HIV is an infection that can be passed on by sexual contact and from a mother to her foetus.
Asexual reproduction and mitosis
define asexual reproduction as the process resulting in the production of genetically identical offspring from one parent
state that mitosis is a type of cell division giving rise to genetically identical cells in which the chromosome number is maintained
state the importance of mitosis in growth, repair and asexual reproduction
Asexual reproduction is the process that produces genetically identical offspring from one parent, and in organisms whose cells have a nucleus, the new cells are made by mitosis, a type of cell division that keeps the chromosome number the same.
- Asexual reproduction
- Asexual reproduction: the process resulting in the production of genetically identical offspring from one parent, without the fusion of the nuclei of gametes
- Offspring
- Offspring: the new organisms produced by reproduction supports K325-13(a)
- Clone
- Clone: a group of organisms, or of cells, that are genetically identical to each other supports K325-13(a)
- Gamete
- Gamete: a sex cell, such as a sperm or an egg cell, which carries one set of chromosomes and can fuse with another gamete supports K325-13(a)
- Vegetative propagation
- Vegetative propagation: a type of asexual reproduction in which a part of a plant, such as a piece of stem, root or leaf, grows into a whole new plant
- Chromosome
- Chromosome: a thread-like structure in the nucleus, made of DNA, which carries the genes supports K325-13(b)
Asexual reproduction: the four common types
| Type | How it happens | Examples |
|---|---|---|
| Binary fission | A single-celled organism divides into two daughter cells that are identical, and each daughter cell then grows to full size. | Amoeba and bacteria reproduce by binary fission. |
| Budding | A small outgrowth called a bud grows on the parent, and it breaks off to become a new individual. | Yeast and Hydra reproduce by budding. |
| Spore formation | The parent makes many tiny spores, and each spore can grow into a new individual when the conditions are suitable, with no fusion of gametes. | Bread mould, which is a fungus, reproduces by spore formation. |
| Vegetative propagation | A part of the parent plant, such as a stem, a root or a leaf, grows into a whole new plant. | Potato tubers, strawberry runners and stem cuttings can all grow into new plants. |
Vegetative propagation in flowering plants
Runners
A strawberry plant sends out long horizontal stems, called runners, and new plants grow from the buds along them. supports K325-13(a)
Tubers
A potato tuber is a swollen underground stem, and each bud on it can grow into a new potato plant. supports K325-13(a)
Cuttings
A piece of stem, cut from a plant and placed in soil or water, can grow roots and become a new plant. supports K325-13(a)
Why asexual reproduction is useful, and where it falls short
| Advantage of asexual reproduction | Explanation |
|---|---|
| Favourable traits are passed on | The offspring are genetically identical to the parent, so favourable characteristics are passed on to the offspring (apart from rare mutations). |
| No energy spent on reproductive organs | The organism does not need to make flowers, gametes or other reproductive organs, so it saves energy. |
| No need to find a mate or wait for fertilisation | One parent is enough and no fertilisation is needed, so the organism can reproduce faster and colonise a new area quickly. |
- The offspring are all genetically identical, so there is no variation, and a disease or a change in the environment that harms one individual is likely to harm all of them. supports K325-13(a)
- Many offspring are produced close to the parent, so they compete for the same light, water and mineral ions. supports K325-13(a)
Mitosis: identical cells, same chromosome number
Mitosis is a type of cell division that gives rise to genetically identical cells, and the chromosome number is maintained, so each daughter cell has the same number of chromosomes as the parent cell.
- 1Before the cell divides, it copies its DNA, so each chromosome becomes two identical copies that are joined together.
- 2The two copies of each chromosome are separated and pulled to opposite ends of the cell, and a nucleus forms around each set.
- 3The cell then divides into two daughter cells, and each daughter cell has the same number of chromosomes and the same genes as the parent cell.
Where it happens
Mitosis takes place in body cells, and in a human body cell it produces two daughter cells that each have 46 chromosomes. supports K325-13(b)
What it makes
Mitosis makes two daughter cells that are genetically identical to each other and to the parent cell.
Chromosome number
The chromosome number is maintained, which means it stays the same in the daughter cells as in the parent cell.
Why mitosis matters: growth, repair and asexual reproduction
Growth
Mitosis increases the number of cells, so a zygote grows into a multicellular organism, and a child grows into an adult.
Repair
Mitosis makes new cells to replace cells that are damaged or dead, for example when the skin heals after a cut.
Asexual reproduction
Mitosis makes the cells from which the offspring of asexual reproduction develop, so the offspring are genetically identical to the parent.
- Mitosis also replaces cells that wear out during normal life, such as the cells on the surface of the skin and the cells lining the gut. supports K325-13(c)
Depth: why and how
- Why are the offspring genetically identical to the parent? Mitosis copies the DNA exactly before the cell divides, so every daughter cell receives the same genes as the parent cell.
- Why can asexual reproduction spread a population quickly? One parent alone can produce offspring and no fertilisation is needed, so a single organism can start a new population.
- Why is a population of clones at risk? All the individuals have the same genes, so they all have the same weaknesses, and one disease could affect them all.
- Cross-link to Cell structure: the chromosomes are in the nucleus of the cell, and the cell membrane holds the cytoplasm together as the cell divides.
- Cross-link to Nutrition in flowering plants: a plant that reproduces by vegetative propagation uses the food stored in the tuber, stem or root to grow its first shoots.
- The offspring of asexual reproduction are identical apart from rare changes in DNA called mutations, which can happen when DNA is copied. For SEAB answers, write that the offspring are genetically identical. supports K325-14(h)
Common mistakes
Asexual reproduction needs two parents to make clones.
Asexual reproduction needs only one parent.
The offspring of asexual reproduction are similar to the parent.
The offspring of asexual reproduction are genetically identical to the parent.
Mitosis halves the number of chromosomes.
Mitosis maintains the chromosome number, and it is meiosis that halves it.
Mitosis makes the gametes.
Mitosis makes genetically identical cells for growth, repair and asexual reproduction, and gametes are made by meiosis.
Mitosis is for the GRA: Growth, Repair, Asexual reproduction.
Decode key for GRA: G = Growth; R = Repair; A = Asexual reproduction.Asexual reproduction needs only one parent, and it gives genetically identical offspring (by mitosis in organisms that have a nucleus), which is quick but gives no variation.
Exam check: K325-13(a)
Q1 Which statement defines asexual reproduction?
- A Two parents make offspring that are all different
- B Two gametes fuse to make a zygote
- C One parent produces genetically identical offspring
- D One parent produces gametes by meiosis
Show answer
MCQ answer key C (One parent produces genetically identical offspring): asexual reproduction is the production of genetically identical offspring from one parent, so it needs no fusion of gametes.
Q2 Which is an example of vegetative propagation?
- A A potato tuber growing into a new plant
- B Yeast forming a bud
- C A bacterium dividing in two
- D Bread mould releasing spores
Show answer
MCQ answer key A (A potato tuber growing into a new plant): a potato tuber is part of a plant that grows into a new plant, which is vegetative propagation, whereas the others are budding, binary fission and spore formation.
Q3 Why is asexual reproduction an advantage in a stable environment?
- A It produces variation in the offspring
- B It needs two parents
- C It uses energy to make flowers
- D It passes on favourable traits to the offspring
Show answer
MCQ answer key D (It passes on favourable traits to the offspring): the offspring are genetically identical to the parent, so favourable characteristics are passed on to the offspring (apart from rare mutations), in a stable environment where they suit the surroundings.
Structured Hydra is a small animal that can reproduce by budding.
- State one type of asexual reproduction, other than budding, shown by a named organism. [1]
- State why the new Hydra is genetically identical to its parent. [2]
- State one disadvantage to a species of reproducing only asexually. [1]
Total: 4 marks
Show mark scheme
(a) 1 mark
- Mark scheme: any one of: binary fission in Amoeba or bacteria, OR spore formation in bread mould, OR vegetative propagation in a potato or a strawberry plant
(b) 2 marks
- Mark scheme: the bud is made by mitosis
- Mark scheme: mitosis gives genetically identical cells with the same chromosome number as the parent cell
(c) 1 mark
- Mark scheme: there is no genetic variation, so all the individuals may be harmed by the same disease or the same change in the environment
Exam check: K325-13(b)
Q1 What is the effect of mitosis on the chromosome number of a cell?
- A It is halved
- B It is maintained
- C It is doubled
- D It is lost
Show answer
MCQ answer key B (It is maintained): mitosis gives daughter cells with the same chromosome number as the parent cell, so the number is maintained.
Q2 A human skin cell has 46 chromosomes and divides by mitosis. How many chromosomes are in each daughter cell?
- A 46
- B 23
- C 92
- D 44
Show answer
MCQ answer key A (46): the chromosome number is maintained in mitosis, so each daughter cell has 46 chromosomes.
Q3 How do the daughter cells made by mitosis compare with each other?
- A They are genetically different
- B They have half the chromosomes of the parent cell
- C They are genetically identical
- D They are all gametes
Show answer
MCQ answer key C (They are genetically identical): mitosis gives genetically identical cells with the same chromosome number as the parent cell.
Structured A cell divides by mitosis.
- State what is meant by mitosis. [2]
- The parent cell has 12 chromosomes. State the number in each daughter cell. [1]
- State why the DNA is copied before the cell divides. [1]
Total: 4 marks
Show mark scheme
(a) 2 marks
- Mark scheme: a type of cell division
- Mark scheme: that gives genetically identical cells in which the chromosome number is maintained
(b) 1 mark
- Mark scheme: 12
(c) 1 mark
- Mark scheme: so that each daughter cell receives a full set of chromosomes and the same genes as the parent cell
Exam check: K325-13(c)
Q1 Which process uses mitosis to replace damaged cells?
- A Growth
- B Repair
- C Fertilisation
- D Pollination
Show answer
MCQ answer key B (Repair): mitosis makes new cells to replace damaged or dead cells, which is repair.
Q2 A zygote becomes a multicellular organism mainly because of
- A meiosis
- B fertilisation
- C pollination
- D mitosis
Show answer
MCQ answer key D (mitosis): mitosis increases the number of cells, and this is how a zygote grows into a multicellular organism.
Q3 Which list gives all three uses of mitosis named in the syllabus?
- A Growth, repair and gamete formation
- B Repair, fertilisation and asexual reproduction
- C Growth, repair and asexual reproduction
- D Growth, meiosis and repair
Show answer
MCQ answer key C (Growth, repair and asexual reproduction): the three uses are growth, repair and asexual reproduction, and gamete formation is done by meiosis.
Structured A student cuts her finger and the wound heals in a few days.
- Name the type of cell division that makes the new skin cells. [1]
- Explain why the new skin cells are suitable replacements. [2]
- State two other uses of mitosis in living organisms. [2]
Total: 5 marks
Show mark scheme
(a) 1 mark
- Mark scheme: mitosis
(b) 2 marks
- Mark scheme: they are genetically identical to the old cells
- Mark scheme: they have the same number of chromosomes as the old cells
(c) 2 marks
- Mark scheme: growth
- Mark scheme: asexual reproduction
Sexual reproduction, chromosomes and meiosis
define sexual reproduction as the process involving the fusion of nuclei of male and female gametes to form a zygote and the production of genetically dissimilar offspring
define the terms haploid and diploid, and explain the need for a reduction division process prior to fertilisation in sexual reproduction
state what is meant by homologous pairs of chromosomes
state that meiosis is a type of cell division that gives rise to genetically dissimilar cells in which the chromosome number is halved due to the separation of homologous chromosomes
state that meiosis is used in the formation of gametes
Sexual reproduction is the process involving the fusion of the nuclei of male and female gametes to form a zygote, and it produces genetically dissimilar offspring.
- Sexual reproduction
- Sexual reproduction: the process involving the fusion of the nuclei of male and female gametes to form a zygote, and the production of genetically dissimilar offspring
- Fertilisation
- Fertilisation: the fusion of the nucleus of a male gamete with the nucleus of a female gamete supports K325-13(d)
- Zygote
- Zygote: the single cell formed when the nuclei of a male gamete and a female gamete fuse; it has the diploid chromosome number and divides by mitosis to form the embryo supports K325-13(d)
- Diploid
- Diploid: a cell that has two complete sets of chromosomes, one set from each parent; it is written as 2n, and a human body cell has 46 chromosomes supports K325-13(e)
- Haploid
- Haploid: a cell that has one complete set of chromosomes; it is written as n, and a human gamete has 23 chromosomes supports K325-13(e)
- Homologous pair
- Homologous pair: two chromosomes, one from each parent, that have the same shape, size and length and the same genes at the same positions, although they may carry different alleles of those genes supports K325-13(f)
- Gene
- Gene: a length of DNA on a chromosome that codes for one characteristic supports K325-13(f)
- Allele
- Allele: one of the different versions of the same gene supports K325-13(f)
- Reduction division
- Reduction division: a cell division in which the chromosome number is halved, and meiosis is the reduction division that makes gametes supports K325-13(e)
Chromosomes: diploid, haploid and homologous pairs
| Cell | Chromosome number in a human | Diploid or haploid |
|---|---|---|
| Body cell, such as a skin cell | A human body cell has 46 chromosomes, which are arranged as 23 homologous pairs. | A body cell is diploid. |
| Gamete, a sperm or an egg cell | A human gamete has 23 chromosomes, one from each homologous pair. | A gamete is haploid. |
| Zygote | A zygote has 46 chromosomes, of which 23 came from the father and 23 came from the mother. | A zygote is diploid. |
Why a reduction division is needed before fertilisation
- 1Gametes are made by a division that halves the chromosome number, so each gamete is haploid.
- 2At fertilisation, the nucleus of the male gamete fuses with the nucleus of the female gamete, so the two haploid sets join.
- 3The zygote is therefore diploid, so the chromosome number of the species stays constant from one generation to the next.
- Without a reduction division, the gametes would be diploid, so the zygote would have double the chromosome number, and the number would double again in every generation.
This is why a reduction division is needed before fertilisation: it halves the chromosome number in the gametes, so that fertilisation restores the diploid number.
Meiosis: the reduction division
Meiosis is a type of cell division that gives rise to genetically dissimilar cells in which the chromosome number is halved, because the homologous chromosomes are separated.
- 1A diploid cell in the sex organs, with its homologous pairs of chromosomes, starts to divide.
- 2The chromosomes are copied, and then the homologous chromosomes of each pair are separated into different cells.
- 3A second division then separates the copies, so four daughter cells are formed, and each is haploid, with one chromosome from each homologous pair.
- 4Each gamete has a different combination of chromosomes, because one chromosome from each homologous pair goes into each gamete at random, so the four cells are genetically different.
In humans
In humans, meiosis takes place in the testes, where it forms sperm, and in the ovaries, where it forms egg cells. supports K325-13(h)
In flowering plants
In flowering plants, meiosis takes place in the anthers, in the cells that lead to the pollen grains, and in the ovules, in the cells that lead to the ovum; for SEAB answers, write that the gametes are formed by meiosis, so they are haploid. supports K325-13(h)
What it is used for
Meiosis is used in the formation of gametes, so the gametes are haploid, and it takes place in the sex organs of organisms that reproduce sexually.
Mitosis compared with meiosis
| Feature | Mitosis | Meiosis |
|---|---|---|
| Type of cells made | Mitosis makes body cells, and the cells made are genetically identical to each other and to the parent cell. | Meiosis makes gametes, and the cells made are genetically different from each other and from the parent cell. |
| Number of daughter cells | A cell that divides by mitosis gives two daughter cells. | A cell that divides by meiosis gives four daughter cells. |
| Chromosome number | In mitosis, the daughter cells have the same chromosome number as the parent cell, so the number is maintained. | In meiosis, the daughter cells have half the chromosome number of the parent cell, so the number is halved. |
| Homologous chromosomes | In mitosis, the homologous chromosomes stay in the same cell. | In meiosis, the homologous chromosomes are separated into different cells. |
| Diploid or haploid | Mitosis usually takes place in diploid cells and makes diploid cells. | Meiosis takes place in a diploid cell and makes haploid cells. |
| Where and why | Mitosis is used for growth, repair and asexual reproduction, in cells all over the body. | In humans and in flowering plants, meiosis is used in the formation of the gametes, in the sex organs. |
- Meiosis gives variation because each gamete receives one chromosome from each homologous pair, and which chromosome of the pair goes into each gamete is random.
- Fertilisation adds more variation, because any sperm can fuse with any egg cell, so many different combinations of chromosomes are possible in a zygote. supports K325-13(g)
Sexual and asexual reproduction compared
| Feature | Asexual reproduction | Sexual reproduction |
|---|---|---|
| Number of parents | Asexual reproduction needs one parent. | Sexual reproduction usually needs two parents, a male and a female. |
| Gametes and fusion | No gametes are made and there is no fusion of nuclei. | Gametes are made by meiosis, and their nuclei fuse at fertilisation. |
| Offspring | The offspring are genetically identical to the parent. | The offspring are genetically different from each other and from the parents. |
| Speed and energy | It is quick, and the organism does not need to make reproductive organs. | It is slower, and the organism needs energy to make reproductive organs and gametes and to find a mate. |
| Examples | Amoeba, yeast, bread mould and strawberry plants reproduce asexually. | Humans reproduce sexually, and flowering plants can reproduce sexually (and some also asexually). |
Why sexual reproduction is an advantage
Variation helps the species survive
The variation between offspring means that some individuals may be able to survive a sudden change in the environment, so there is less risk that the whole species is wiped out.
Traits from both parents
The offspring can inherit favourable characteristics from both parents.
Adaptation over time
Variation gives natural selection something to act on, so a species that reproduces sexually can adapt to a changing environment over many generations. supports K325-13(d)
Depth: why and how
- Why does the zygote have the diploid number of chromosomes? The male gamete brings a haploid set and the female gamete brings a haploid set, so the zygote has two sets.
- Why are the four cells made by meiosis genetically different? Each cell receives a random one from each homologous pair, so each has a different combination of chromosomes.
- Why do homologous chromosomes carry the same genes? One came from the father and one from the mother, and each carries genes for the same characteristics in the same order, though the alleles may differ.
- What if meiosis did not happen? Human gametes would have 46 chromosomes, and a zygote would have 92, which shows why the reduction division is essential.
- Cross-link to Inheritance: the alleles on the chromosomes are the reason that offspring show different combinations of characteristics.
- Cross-link to Cell structure: the nucleus contains the chromosomes, and the fusion of the two gamete nuclei is what forms the nucleus of the zygote.
Common mistakes
Meiosis makes cells that are genetically identical.
Meiosis makes cells that are genetically different, and mitosis makes cells that are genetically identical.
Gametes are diploid, with 46 chromosomes.
Gametes are haploid, so a human gamete has 23 chromosomes.
Homologous chromosomes are exact copies of each other.
Homologous chromosomes are a pair, one from each parent, with the same genes in the same positions, but they may carry different alleles.
Haploid means half a cell.
Haploid means that a cell has one complete set of chromosomes.
Fertilisation is when a sperm enters an egg cell.
Fertilisation is the fusion of the nucleus of a male gamete with the nucleus of a female gamete.
Meiosis makes gametes that are HALF: Haploid cells are made, four from each diploid cell; Any one chromosome from each homologous pair can go into a gamete, which gives variation; Lowers the chromosome number to half; Fertilisation restores the diploid number.
Decode key for HALF: H = Haploid cells are made, four from each diploid cell; A = Any one chromosome from each homologous pair can go into a gamete, which gives variation; L = Lowers the chromosome number to half; F = Fertilisation restores the diploid number.Meiosis halves the chromosome number to make haploid gametes, and fertilisation restores the diploid number, so the chromosome number of the species stays constant and the offspring are genetically different.
Exam check: K325-13(d)
Q1 Which event is part of sexual reproduction?
- A One parent divides into two identical cells
- B The nuclei of a male gamete and a female gamete fuse
- C A piece of stem grows into a new plant
- D A bud breaks off from the parent
Show answer
MCQ answer key B (The nuclei of a male gamete and a female gamete fuse): sexual reproduction involves the fusion of the nuclei of male and female gametes to form a zygote.
Q2 How is a zygote formed?
- A Fertilisation of a female gamete by a male gamete
- B Mitosis of a body cell
- C Meiosis of a zygote
- D Budding of a parent
Show answer
MCQ answer key A (Fertilisation of a female gamete by a male gamete): the zygote is formed when the nuclei of a male gamete and a female gamete fuse.
Q3 Why does sexual reproduction give offspring that are genetically dissimilar?
- A The gametes are made by mitosis
- B Only one parent is needed
- C The offspring are cloned
- D The gametes are different and their nuclei fuse
Show answer
MCQ answer key D (The gametes are different and their nuclei fuse): the gametes are genetically different from each other, and fertilisation combines the genes of two parents.
Structured A farmer grows a crop of identical plants from cuttings, and another farmer grows a crop from seeds.
- State the type of reproduction used by the first farmer. [1]
- Explain why the plants grown from seeds are genetically different from each other. [2]
- State one advantage to the species of the plants being genetically different. [1]
Total: 4 marks
Show mark scheme
(a) 1 mark
- Mark scheme: asexual reproduction
(b) 2 marks
- Mark scheme: seeds are produced by sexual reproduction, in which the nuclei of male and female gametes fuse
- Mark scheme: the gametes are genetically different, so each zygote has a different combination of genes
(c) 1 mark
- Mark scheme: some may survive a sudden change in the environment or a disease, so the species is less likely to be wiped out
Exam check: K325-13(e)
Q1 A human body cell has 46 chromosomes. How many chromosomes does a human gamete have?
- A 92
- B 46
- C 23
- D 44
Show answer
MCQ answer key C (23): a gamete is haploid, so it has half the chromosome number of a diploid body cell.
Q2 What is the reason for a reduction division before fertilisation?
- A To keep the chromosome number the same in the next generation
- B To make the gametes identical
- C To make more cells for growth
- D To copy the DNA
Show answer
MCQ answer key A (To keep the chromosome number the same in the next generation): halving the chromosome number in the gametes means that fertilisation restores the diploid number, so the chromosome number stays constant.
Q3 Which describes a diploid cell?
- A It has one set of chromosomes
- B It has no chromosomes
- C It has half a nucleus
- D It has two sets of chromosomes
Show answer
MCQ answer key D (It has two sets of chromosomes): a diploid cell has two complete sets of chromosomes, one from each parent.
Structured The cells of a fruit fly have 8 chromosomes, and fruit flies reproduce sexually.
- State the number of chromosomes in a gamete of the fruit fly. [1]
- State the number of chromosomes in the zygote. [1]
- Explain why the gametes must have this number of chromosomes. [2]
Total: 4 marks
Show mark scheme
(a) 1 mark
- Mark scheme: 4
(b) 1 mark
- Mark scheme: 8
(c) 2 marks
- Mark scheme: so that fertilisation restores the diploid number
- Mark scheme: otherwise the chromosome number would double in every generation
Exam check: K325-13(f)
Q1 What is a homologous pair of chromosomes?
- A Two identical copies made by copying DNA
- B Two chromosomes, one from each parent, with the same genes in the same positions
- C Two chromosomes from the same parent
- D Two different chromosomes with different genes
Show answer
MCQ answer key B (Two chromosomes, one from each parent, with the same genes in the same positions): the two chromosomes of a homologous pair are one from each parent, with the same genes at the same positions, though the alleles may differ.
Q2 How many homologous pairs are in a human body cell?
- A 23
- B 46
- C 22
- D 92
Show answer
MCQ answer key A (23): a human body cell has 46 chromosomes, which is 23 pairs.
Q3 Which statement about the two chromosomes of a homologous pair is correct?
- A They must carry the same alleles
- B They come from the same parent
- C They are the same length and carry the same genes
- D They carry different genes
Show answer
MCQ answer key C (They are the same length and carry the same genes): the chromosomes of a homologous pair are the same length and carry the same genes, although they may carry different alleles.
Structured The diagram shows a homologous pair of chromosomes in a cell.
- State what is meant by a homologous pair of chromosomes. [2]
- State one way in which the two chromosomes of the pair can differ. [1]
- State the stage of a life cycle at which the two chromosomes of a pair are brought together in one cell. [1]
Total: 4 marks
Show mark scheme
(a) 2 marks
- Mark scheme: two chromosomes, one from each parent
- Mark scheme: with the same shape, size and length and the same genes in the same positions
(b) 1 mark
- Mark scheme: they may carry different alleles of the same genes
(c) 1 mark
- Mark scheme: fertilisation
Exam check: K325-13(g)
Q1 What is the result of meiosis?
- A Two genetically identical diploid cells
- B Four genetically different haploid cells
- C Two genetically different haploid cells
- D Four genetically identical diploid cells
Show answer
MCQ answer key B (Four genetically different haploid cells): meiosis gives four genetically different haploid cells, because the homologous chromosomes are separated.
Q2 Which change to the chromosomes takes place in meiosis?
- A The chromosome number is maintained
- B The DNA is not copied
- C The cells become diploid
- D The homologous chromosomes are separated into different cells
Show answer
MCQ answer key D (The homologous chromosomes are separated into different cells): in meiosis, the homologous chromosomes are separated, and the chromosome number is halved.
Q3 Which feature is found in meiosis but not in mitosis?
- A The cells produced are genetically identical
- B The DNA is copied before division
- C The chromosome number is halved
- D It takes place in the nucleus
Show answer
MCQ answer key C (The chromosome number is halved): meiosis halves the chromosome number, and mitosis maintains it.
Structured The diagram shows a parent cell with four chromosomes that divides by meiosis.
- State the number of chromosomes in each cell produced. [1]
- State how the cells produced by meiosis differ from the cells produced by mitosis. [2]
- Explain how meiosis leads to variation. [2]
Total: 5 marks
Show mark scheme
(a) 1 mark
- Mark scheme: 2
(b) 2 marks
- Mark scheme: meiosis gives cells that are genetically different, mitosis gives cells that are genetically identical
- Mark scheme: meiosis halves the chromosome number, mitosis maintains it
(c) 2 marks
- Mark scheme: each gamete receives one chromosome from each homologous pair
- Mark scheme: which chromosome of each pair goes into a gamete is random, so each gamete has a different combination
Exam check: K325-13(h)
Q1 Which cells are made by meiosis?
- A Skin cells
- B Gametes
- C Red blood cells
- D Zygotes
Show answer
MCQ answer key B (Gametes): meiosis is used in the formation of gametes.
Q2 In which organ of a human male does meiosis take place?
- A Testis
- B Prostate gland
- C Sperm duct
- D Urethra
Show answer
MCQ answer key A (Testis): meiosis takes place in the testis, where sperm are formed.
Q3 Which is the reason that meiosis is used to make gametes?
- A It makes gametes that are genetically identical
- B It makes more skin cells
- C It repairs damaged gametes
- D It halves the chromosome number, so fertilisation does not double it
Show answer
MCQ answer key D (It halves the chromosome number, so fertilisation does not double it): meiosis halves the chromosome number in gametes, so that the zygote has the diploid number.
Structured A student says that all cell divisions in the human body are mitosis.
- State the type of cell division used to make gametes. [1]
- Name two organs in which this type of cell division takes place in a woman and a man. [2]
- State why the gametes are made by this type of division and not by mitosis. [2]
Total: 5 marks
Show mark scheme
(a) 1 mark
- Mark scheme: meiosis
(b) 2 marks
- Mark scheme: ovary in a woman
- Mark scheme: testis in a man
(c) 2 marks
- Mark scheme: mitosis would keep the chromosome number the same, so the gametes would be diploid
- Mark scheme: then fertilisation would double the chromosome number in the zygote
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- The flower and its parts
- Pollination
- Fertilisation in flowering plants
- The male and female reproductive systems
- The menstrual cycle
- Fertilisation, early development and the foetus
- HIV and sexually transmitted infections
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Notes version 1.0 · Last updated 30 Sept 2026 · Topic 13 of 14