Reproduction, meiosis and DNA – GCSE Biology exam questions with mark scheme

1Grade 1–3Foundation3 marks

(a) The genetic material in the nucleus of a cell is DNA. Complete the sentence.
DNA is a polymer made from two strands forming a ____________. [1]

(b) What is a gene? [1]

(a) double helix(1)
(b) a small section of DNA (on a chromosome) that codes for a particular sequence of amino acids / a specific protein
allow (small) section of a chromosome for section of DNA
'section of DNA' alone is not enough: the answer must say what it codes for (protein / amino acid sequence)
ignore 'codes for / controls a characteristic' unless protein or amino acids also given(1)
(c) the entire/all the genetic material of that organism
allow all the DNA of an organism(1)
Answer: (a) Double helix (b) Section of DNA coding for a specific protein (c) All of the organism's genetic material.
Examiner tip: 'A gene is DNA' is too vague – say it is a section of DNA coding for a protein.

2Grade 4–56 marks

Gametes are produced by meiosis.

(a) Name one organ in the human body where meiosis takes place. [1]

(b) A human body cell contains 46 chromosomes. How many chromosomes are in a human sperm cell? [1]

(d) Give two differences between the cells produced by meiosis and the cells produced by mitosis. [2]

(a) testis / ovary
allow testes / ovaries / testicle(s) / gonad(s)
ignore reproductive organ(s) alone
reject uterus / womb / penis(1)
(b) 23(1)
(c) (two gametes) join at fertilisation(1)
(c) so the normal/full number of chromosomes (46) is restored in the zygote/offspring
allow so the chromosome number does not double (each generation)(1)
(d) any two from:
• meiosis produces four cells whereas mitosis produces two
• meiosis produces genetically different cells whereas mitosis produces genetically identical cells
• cells from meiosis have half the number of chromosomes / one set (23) whereas cells from mitosis have the full number / two sets (46) (allow haploid vs diploid)
• meiosis produces gametes / sex cells whereas mitosis produces body cells
each difference must compare both processes(1)
(d) a second difference from the list(1)
Answer: (a) Testis or ovary (b) 23 (c) Fertilisation restores 46 chromosomes (d) Four vs two cells; different vs identical.
Examiner tip: In (d), each difference must be a comparison – say what both processes produce.

3Grade 1–3Foundation4 marks

Some organisms reproduce sexually and some reproduce asexually.

(a) Complete the table. Put a tick (✓) in each row to show whether the statement is true for sexual reproduction or for asexual reproduction. [3]

Statement	Sexual	Asexual
Only one parent is needed
Gametes fuse together
The offspring are clones of the parent

(b) Name the type of cell division that takes place in asexual reproduction. [1]

(a) only one parent is needed: asexual
a row with two ticks scores 0 for that row(1)
(a) gametes fuse together: sexual(1)
(a) offspring are clones of the parent: asexual(1)
(b) mitosis
reject meiosis(1)
Answer: (a) asexual; sexual; asexual (b) mitosis
Examiner tip: Students mix up mitosis and meiosis in (b): asexual reproduction makes identical cells, so it uses mitosis. Meiosis is only used to make gametes.

4Grade 1–35 marks

The diagram shows how the genetic material is arranged in a human cell. Each part is shown at a higher magnification than the part before it.

(a) Which letter, A, B, C or D, shows a gene? [1]

(b) Name structure B. [1]

chromosome gene nucleus

(d) Scientists have worked out the whole human genome.

Give two ways that understanding the human genome is useful. [2]

(a) D(1)
(b) chromosome
allow chromatid(s)
reject DNA / gene(1)
(c) gene, chromosome, nucleus (all three in the correct order)(1)
(d) any two from:
• to search for / find genes linked to different types of disease
• to understand and treat inherited disorders
allow to develop (new) treatments / cures for inherited disorders / genetic diseases
• to trace human migration patterns from the past
allow to find out where (our) ancestors came from / how humans spread across the world
ignore 'to cure diseases' with no link to genes or inheritance(1)
(d) a second way from the list(1)
Answer: (a) D (b) chromosome (c) gene → chromosome → nucleus (d) e.g. find genes linked to disease; treat inherited disorders; trace human migration
Examiner tip: In (d) 'to cure diseases' is too vague: link it to genes or inherited disorders, or give migration as a separate, safer point.

5Grade 4–57 marks

A horse has 64 chromosomes in each of its body cells.

(a) How many chromosomes are there in a horse egg cell? [1]

(b) Sperm cells are made in the testes by meiosis. Each cell that divides by meiosis produces four sperm cells.

Calculate the number of sperm cells produced when $2.5 \times 10^{5}$ cells divide by meiosis.

Give your answer in standard form. [2]

(i) How many cells are there after the zygote has divided 4 times? [1]

(ii) How many chromosomes are in each of these cells? [1]

(d) Explain why the foal that develops is not genetically identical to either of its parents. [2]

(a) 32(1)
(b) $4 \times 2.5 \times 10^{5}$ or 1 000 000(1)
(b) $1(.0) \times 10^{6}$
correct answer in standard form gains 2 marks
1 000 000 not in standard form gains 1 mark only(1)
(c)(i) 16(1)
(c)(ii) 64
allow 64 even if (c)(i) is wrong(1)
(d) gametes / sex cells / sperm and egg are produced by meiosis so are genetically different (from each other)
allow meiosis produces variation(1)
(d) at fertilisation (the nuclei of) two gametes fuse, so genetic information from both parents is mixed
allow foal gets half its chromosomes / alleles from each parent
ignore 'sexual reproduction' alone(1)
Answer: (a) 32 (b) $1.0 \times 10^{6}$ (c)(i) 16 (ii) 64 (d) gametes from meiosis are genetically different; fertilisation mixes genetic information from two parents
Examiner tip: In (c)(ii) many students halve the number again: mitosis keeps the full chromosome number, so every embryo cell still has 64.

6Grade 6–7HigherTriple only7 marks

DNA is a polymer made of many repeating units.

(a) Name the repeating units that make up DNA. [1]

(b) The base sequence on one strand of a short section of DNA is:

T A C G G A T T C A A G

Give the base sequence on the complementary strand. [1]

(d) In a sample of DNA from a bacterium, 18% of the bases are thymine (T).

Calculate the percentage of bases that are guanine (G). [2]

(e) Proteins are made on ribosomes. Describe the role of carrier molecules in protein synthesis. [2]

(a) nucleotides(1)
(b) A T G C C T A A G T T C
all 12 bases correct for the mark
reject any answer containing U(1)
(c) 4
(12 bases ÷ 3 bases per amino acid)(1)
(d) A = 18% (so A + T = 36%) or 100 − 36 = 64(1)
(d) 32(%)
correct answer with no working gains 2 marks(1)
(e) carrier molecules bring (specific) amino acids to the ribosome
allow carry / transport for bring(1)
(e) in the correct order (to match the template / the base sequence)
allow (so that) the amino acids are joined together (to form a protein / polypeptide)
ignore mRNA / tRNA / codon (detail not required) but do not penalise correct use(1)
Answer: (a) nucleotides (b) ATGCCTAAGTTC (c) 4 (d) 32% (e) bring specific amino acids to the ribosome in the correct order to be joined into a protein
Examiner tip: In (d) students often stop at 64%: that is guanine + cytosine together, and it must be halved because G pairs with C.

7Grade 6–7Triple only7 marks

Aphids are small insects that feed on plant sap.

In summer, female aphids reproduce asexually. They give birth to young without mating.

A student counted the aphids on one rose plant once a week during the summer. The graph shows the results.

(a) How many aphids were on the plant at week 4? [1]

(b) Calculate the mean rate of increase in the number of aphids between week 1 and week 4.

Give the unit. [2]

(d) In autumn, aphids reproduce sexually. They lay eggs which survive the winter and hatch in spring.

Suggest why it is an advantage to the aphids to reproduce sexually at this time of year. [2]

(a) 600(1)
(b) (600 − 100) ÷ 3(1)
(b) 167 aphids per week
allow 166.7 / 166.67
allow aphids/week or aphids per week; the unit must be given for this mark
167 with no unit scores 1 mark
allow ecf from (a)(1)
(c) only one parent is needed / no need to find a mate
allow every aphid can produce offspring(1)
(c) it is faster (than sexual reproduction)
allow no gametes are needed / no fertilisation, so less time and energy used
allow (when conditions are favourable) many identical offspring are produced quickly
ignore 'it is easier'(1)
(d) produces variation in the offspring
ignore 'mixes genes' unless linked to variation(1)
(d) so some (offspring) are more likely to survive if conditions change, e.g. a cold winter / new disease / new predator
allow (variation) increases the chance of survival of the species by natural selection(1)
Answer: (a) 600 (b) 167 aphids per week (c) only one parent needed and faster, so many offspring quickly (d) variation, so some offspring may survive changed winter conditions (natural selection)
Examiner tip: In (d) 'it gives variation' only earns one mark: link the variation to survival when conditions change to get the second.

8Grade 6–76 marks

The common frog reproduces sexually. Each body cell of a frog contains 26 chromosomes.

Explain how a frog egg cell and a frog sperm cell are produced, and how they lead to a tadpole that:

has 26 chromosomes in each of its body cells
is genetically different from both of its parents
contains many different types of cell.

[6]

eggs and sperm (gametes) are made by meiosis (in the ovaries and testes)(1)
before meiosis the genetic information / DNA / chromosomes are copied(1)
the cell divides twice to form four gametes(1)
each gamete has half the number of chromosomes / one set: 13 chromosomes(1)
the gametes are all genetically different (from each other)(1)
at fertilisation the egg and sperm (nuclei) fuse / join(1)
so the full number of chromosomes (26) is restored in the zygote / fertilised egg(1)
the zygote has a mixture of genetic information from both parents, so it is genetically different from each parent / shows variation(1)
the zygote / embryo divides by mitosis to grow / increase the number of cells(1)
mitosis produces genetically identical cells, so every body cell has 26 chromosomes(1)
as the embryo develops, cells differentiate / become specialised (to form different tissues / organs)(1)

Level	Marks	What it looks like
Level 3	5–6	A clear, logically linked explanation that covers all three bullet points: meiosis making genetically different gametes with half the number (13), fertilisation restoring 26 and mixing genetic information from two parents, and growth by mitosis with differentiation.
Level 2	3–4	A partly linked explanation covering at least two of the bullet points correctly, e.g. meiosis halves the number and fertilisation restores it, but with little on mitosis / differentiation or on why the tadpole is genetically different.
Level 1	1–2	Some relevant but separate statements, e.g. gametes are made by meiosis, or egg and sperm join at fertilisation. Links between the processes are missing or confused (e.g. mitosis and meiosis swapped).
No marks	0	No relevant content.

Answer: Meiosis (DNA copied, two divisions) gives four genetically different gametes with 13 chromosomes; fertilisation fuses egg and sperm to restore 26 and mix genetic information from both parents; the zygote divides by mitosis (identical cells, 26 each) and cells differentiate into many types.
Examiner tip: Top-level answers cover all three bullets: many students describe meiosis well but forget that mitosis keeps 26 in every body cell and that differentiation gives the different cell types.

9Grade 4–5Triple only7 marks

Daffodils are plants that can reproduce in two ways:

by making seeds in their flowers
by making new bulbs that grow from the parent bulb under the ground.

The table shows information from a daffodil grower.

Method	Number of new plants from one parent each year	Time from planting until the first flowers in years
Seeds	40	5
New bulbs	2	1

(a) Which type of reproduction produces new bulbs? [1]

(b) The grower plants 50 bulbs. Each year, every bulb produces 2 new bulbs. All of the bulbs survive.

Calculate the number of bulbs after 3 years. [2]

Use the information to explain why the grower should use bulbs rather than seeds. [2]

(d) Plant breeders who want to produce new varieties of daffodil grow them from seeds.

Explain why. [2]

(a) asexual(1)
(b) number trebles each year / $50 \times 3 \times 3 \times 3$ or $50 \times 3^{3}$
allow 150 and 450 seen(1)
(b) 1350
correct answer with no working gains 2 marks
300 (50 × 2 × 3) or 400 (50 × 2³) gains 0 marks(1)
(c) (offspring from bulbs are) genetically identical to the parent / clones, so they will have the same flower colour
allow produced by mitosis so no variation(1)
(c) (bulbs) produce flowers sooner: after 1 year instead of 5
allow saves time (and money) before they can be sold(1)
(d) seeds are produced by sexual reproduction, so the offspring show variation / are genetically different(1)
(d) so plants with new / desirable characteristics can be chosen for selective breeding
allow so new combinations of characteristics appear(1)
Answer: (a) asexual (b) 1350 (c) bulbs give clones with the same flower colour, and flower after 1 year not 5 (d) seeds come from sexual reproduction, giving variation from which new varieties can be selected
Examiner tip: In (b) the parent bulb is still there: each year the number becomes 3 times bigger, not 2 times bigger.

10Grade 8–9HigherTriple only7 marks

The table shows some DNA base triplets and the amino acids they code for.

Triplet	Amino acid
AAA	lysine
GAA	glutamic acid
GTA	valine
TGG	tryptophan
GGA	glycine
GGT	glycine

Part of the base sequence of a gene that codes for an enzyme is:

AAA GAA TGG GGA

(a) Give the sequence of amino acids coded for by this part of the gene. [1]

(b) A mutation changes the fifth base in the sequence from A to T.

Which amino acid in the enzyme is changed, and what is it changed to? [1]

(d) A different mutation changes the last base in the sequence from A to T.

Explain why this mutation has no effect on the enzyme. [1]

(e) Some mutations happen in non-coding parts of DNA. They do not change the sequence of amino acids in any protein, but they can still change the phenotype.

Suggest how. [1]

(a) lysine, glutamic acid, tryptophan, glycine (in this order)(1)
(b) glutamic acid is changed to valine
both amino acids needed(1)
(c) the sequence of amino acids is changed, so the protein / enzyme folds into a different shape
allow the chain folds differently(1)
(c) the active site changes shape(1)
(c) so the substrate no longer fits / binds (to the active site)
allow no enzyme-substrate complexes form
reject 'the enzyme is denatured' (unless clearly meaning shape changed by the mutation)
ignore 'the enzyme dies'(1)
(d) the new triplet (GGT) still codes for glycine / the same amino acid, so the amino acid sequence (and the protein) is unchanged(1)
(e) non-coding DNA can switch genes on or off
allow it changes whether a gene is expressed / how much protein is made
ignore 'it changes the gene' alone(1)
Answer: (a) lysine–glutamic acid–tryptophan–glycine (b) glutamic acid → valine (c) different amino acid sequence, protein folds differently, active site changes shape so substrate no longer fits (d) GGT still codes for glycine (e) it can switch a gene on or off
Examiner tip: In (c) students jump straight to 'the substrate won't fit': the chain is amino acid sequence → folding/shape → active site → substrate, and each link is a mark.

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