Cellular Control (6.1.1): OCR A Level Biology Exam Questions by Topic

OCRGenetics, Evolution and EcosystemsExam Questions
Written by Tom Whitburn

Cellular control is a short spec point with only four learning outcomes, but it draws on ideas from right across the course. Spec point 6.1.1 asks you about gene mutations and their effects on proteins, how gene expression is controlled at the transcriptional, post-transcriptional and post-translational levels (the lac operon, transcription factors, splicing and cyclic AMP), how homeobox genes control body plans, and why mitosis and apoptosis matter in shaping the body.

Students usually know the facts. The marks go when the wording slips. Examiners' reports describe students removing introns "from DNA", saying one allele "turns off" another instead of describing the protein it codes for, saying a stop codon ends transcription, and calling the bases or amino acids degenerate. In the six-mark questions, many answers covered one half of the question well and barely touched the other.

Work through the fifteen questions below in order. They start with recall, move on to applying what you know to unfamiliar genes and organisms, and finish with three extended-response questions. If you'd like to go through questions like these with me each week, my OCR A masterclasses run on Wednesdays at 5.15pm for Year 12 and on Tuesdays at 6.30pm or Thursdays at 5.15pm for Year 13.

Want help with this topic? It comes up in my weekly OCR A masterclasses. See the timetable →

What you need from GCSE

Each question on this page assumes you're secure on these GCSE ideas. If any of them feels shaky, look it up before you start.

  • A gene is a section of DNA that codes for a protein; the sequence of bases decides the sequence of amino acids.
  • Proteins are made by transcription (DNA to mRNA in the nucleus) and translation (mRNA to protein at the ribosome).
  • A mutation is a change in the DNA; most have no effect on the phenotype, some change the protein's shape and function.
  • Mitosis produces genetically identical cells for growth and repair; uncontrolled cell division can cause tumours.

Key terms

These words come up in the questions and mark schemes. Examiners expect you to use them exactly.

  • Substitution, insertion and deletion: gene mutations in which a nucleotide is swapped, added or removed; insertions and deletions cause a frameshift.
  • Degenerate code: most amino acids are coded for by more than one triplet, so some substitutions are silent.
  • Nonsense mutation: a mutation that creates a stop codon, so translation ends early and the polypeptide is shorter.
  • lac operon: a group of genes in E. coli (lacZ and lacY) with a shared promoter and operator; lactose binds to the repressor so it leaves the operator and the genes are transcribed.
  • Transcription factor: a protein that binds to DNA (e.g. at a promoter) and switches transcription of a gene on or off.
  • Introns and exons: non-coding and coding sequences; introns are removed from primary mRNA and exons joined to make mature mRNA.
  • Post-translational control: activation of proteins after translation, e.g. cyclic AMP activating protein kinase A.
  • Homeobox and Hox genes: highly conserved regulatory genes in plants, animals and fungi; Hox genes (a subset) control body plan development.
  • Apoptosis: programmed cell death: enzymes break down the cell contents and phagocytes remove the fragments without damaging nearby tissue.

What these questions cover (OCR 6.1.1)

The questions test these learning outcomes from the OCR A Level Biology A specification (H420):

  • (a) types of gene mutations and their possible effects on protein production and function (substitution, insertion and deletion, and beneficial, neutral or harmful effects)
  • (b) the regulatory mechanisms that control gene expression at the transcriptional level, post-transcriptional level and post-translational level (the lac operon, transcription factors, splicing and activation of proteins by cAMP)
  • (c) the genetic control of the development of body plans in different organisms
  • (d) the importance of mitosis and apoptosis as mechanisms controlling the development of body form

How to use this page

Write your answer on paper before you open the mark scheme. Allow about 1.2 minutes per mark: the 15 questions are worth 44 marks, so about 53 minutes in total. Then mark your answer strictly against the mark scheme and read the examiners' tip underneath it. If you'd rather print the questions, download the PDF pack.

Recall

Question 1

A level Paper 2 · June 2022 · Q22(a) · 5 marks · Easy

Complete sentences about the control of body plan, the cell cycle and apoptosis.

Gap-fill passage: body plan is under genetic and ___ control; internal and external ___ influence genes regulating the cell cycle; programmed cell death is called ___; during it ___ digest the cell contents and the products are removed by ___.
Show the mark scheme Mark scheme: environmental; stimuli; apoptosis; enzymes (proteases, caspases); phagocytes or phagocytosis. Lysosomes ignored.

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From the examiners' report: Most students got the first three gaps. The common wrong answers were "hormonal" for environmental and "conditions" for stimuli, and the cell debris is removed by phagocytes, not lysosomes.

Question 2

A level Paper 2 · June 2022 · Q22(b) · 1 mark · Easy

Name the type of gene that controls body plan.

One-line question: state the name of the type of gene responsible for controlling body plan in multicellular organisms.
Show the mark scheme Mark scheme: Hox, homeotic or homeobox genes; "regulatory" ignored.

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From the examiners' report: Nearly everyone scored. Say Hox (homeobox) genes; "regulatory" or "lac operon" were the wrong answers seen.

Question 3

A level Paper 2 · November 2020 · Q16(a) · 5 marks · Medium

Complete a passage about the genes that control body plan, choosing words from a list.

Passage with a word list (analogous, archaea, development, DNA, domains, homeobox, kingdoms, operon, plant, transcription and others): body plan is controlled by ___ genes; their proteins bind to ___ and are ___ factors; the sequence varies little within the animal, ___ or fungus ___.
Show the mark scheme Mark scheme: homeobox; DNA; transcription; plant; kingdoms.

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Question 4

A level Paper 2 · November 2021 · Q16(c)(i) · 2 marks · Easy

Explain why some regions of DNA are described as non-coding.

Question: DNA codes for proteins but some regions are non-coding; explain why some regions of DNA can be described as non-coding.
Show the mark scheme Mark scheme: primary mRNA is edited; introns are removed so are not in mature mRNA; so are not translated; or they are regulatory sequences or code for tRNA or rRNA. "Introns are non-coding" alone ignored.

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From the examiners' report: This asks you to explain, not define. Say that introns are removed from primary mRNA, so they aren't in mature mRNA and aren't translated.

Question 5

A level Paper 2 · November 2021 · Q16(c)(ii) · 1 mark · Easy

Suggest why non-coding regions of DNA show more variation than coding regions.

Question: non-coding regions of DNA show more variation than coding regions, which makes them useful in DNA profiling; suggest why.
Show the mark scheme Mark scheme: mutations there are not selected against (they don't affect survival).

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Question 6

A level Paper 3 · June 2025 · Q4(b) · 2 marks · Hard

Outline how gene expression is regulated at the post-transcriptional level.

Question: outline how gene expression is regulated within cells at the post-transcriptional level.
Show the mark scheme Mark scheme: removal of introns (non-coding mRNA); joining of exons; RNA editing; capping or poly-A tails or spliceosomes also credited.

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From the examiners' report: Stay at the post-transcriptional level: introns are removed from primary mRNA and the exons joined. Introns are not removed from DNA, and the lac operon is transcriptional control.

Applying what you know

Question 7

A level Paper 2 · June 2017 · Q20(b)(iii) · 2 marks · Medium

Explain why E. coli in young mammals are more likely to make the protein that lets lactose in.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Question: a protein is needed for lactose to enter E. coli; E. coli in the gut of young mammals are more likely to have this protein than those in old mammals; suggest an explanation.
Show the mark scheme Mark scheme: young mammals' milk diet means a high lactose concentration; the gene for the protein (lac Y, lactose permease) is transcribed; the protein is lactose permease; lactose removing the repressor from the operator also credited.

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Question 8

A level Paper 3 · June 2018 · Q1(c)(iii) · 2 marks · Hard

Suggest how allele B inhibits the expression of allele A.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Question: suggest how allele B inhibits the expression of allele A (part of a question on gene interaction).
Show the mark scheme Mark scheme: B codes for a repressor protein or transcription factor (or enzyme); it binds to the promoter of A, or to mRNA or a ribosome; so stops transcription or translation of A.

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From the examiners' report: Say what allele B codes for, such as a repressor protein or transcription factor, and that this product binds to the promoter of A and stops its transcription. "B turns off A" gained nothing.

Question 9

A level Paper 3 · June 2025 · Q6(a)(ii) · 1 mark · Hard

State and explain the effect of a mutation on the structure of the β-chain of haemoglobin.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Question: state and explain the effect of mutation 2 on the structure of the β-chain of haemoglobin, with the DNA triplets and genetic code from part (a)(i).
Show the mark scheme Mark scheme: the chain is shorter because an early stop codon has been introduced (nonsense mutation). Frameshift, silent or missense contradict.

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From the examiners' report: Convert the DNA triplets into mRNA codons first. Then say the chain is shorter because a stop codon ends translation early; a stop codon doesn't stop transcription, and this isn't a frameshift.

Question 10

A level Paper 2 · June 2019 · Q17(b)(ii) · 2 marks · Hard

Explain how inserting a new gene into a chromosome could affect other genes on it.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Question: some gene therapy has changed the functioning of other genes; explain how inserting a new gene into a chromosome could affect the functioning of other genes in that chromosome.
Show the mark scheme Mark scheme: frameshift; altered triplets; nearby genes switched on or off; a functioning gene disabled if the new gene is inserted into it. "Mutation" alone ignored.

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From the examiners' report: Focus on "in that chromosome": an insertion inside a gene causes a frameshift and alters the triplets, and one next to a gene can switch it on or off. Epistasis and meiosis are not relevant.

Question 11

A level Paper 2 · June 2017 · Q19(b)(iv) · 1 mark · Medium

Decide what near-identical homeobox genes in humans and chimpanzees tell us about their relationship.

Question: homeobox gene base sequences in humans and chimpanzees are almost identical; what conclusions about their evolutionary relationship can be drawn?
Show the mark scheme Mark scheme: little or none, because homeobox genes are highly conserved across the animal kingdom; it only shows both are animals.

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Question 12

A level Paper 2 · November 2020 · Q16(b)(i) · 2 marks · Medium

Suggest two reasons, other than ethics, why fruit flies are used to research body-plan genes.

Question: fruit flies and mice are used to study genes controlling body plan; besides fewer ethical concerns, suggest two reasons fruit flies are chosen.
Show the mark scheme Mark scheme: low cost; rapid reproduction (many generations in a short time); genetics well understood; simple body plan; mutations visible with a light microscope. "Small" ignored.

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From the examiners' report: "A large number of offspring" wasn't enough: say they reproduce rapidly, so you get many generations in a short time.

Extended answers

Question 13

A level Paper 2 · June 2022 · Q16(b)(iv) · 6 marks · Hard

Use a codon table and levels of protein structure to explain why some mutations do not affect protein function.

Information from earlier in this question:

Earlier part of the same exam question, giving the information this part uses. Six-mark level-of-response question: in sickle cell disease haemoglobin carries less oxygen, but some mutations do not affect protein function; use Fig. 16.3 (codons for amino acids) and levels of protein structure to explain why.
Show the mark scheme Mark scheme indicative points: the genetic code is degenerate; a point mutation may code for the same amino acid (example from Fig. 16.3); silent mutation leaves primary, so tertiary, structure unchanged; a similar amino acid may leave structure unchanged; a change away from the functional site may not matter.

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From the examiners' report: Use all three things asked for: Fig. 16.3, mutations and levels of protein structure. It is the genetic code that is degenerate, not the bases or amino acids.

Question 14

A level Paper 3 · June 2023 · Q6 · 6 marks · Medium

Describe the general roles of homeobox genes and suggest their roles in brain development.

Six-mark level-of-response question: homeobox genes, including Hox genes, code for transcription factors; describe their general roles in the human body and suggest their roles in the development of the brain.
Show the mark scheme Mark scheme indicative points: determine body plan; switch genes on and off; expressed in a set order; regulate mitosis and apoptosis; in the brain, determine head and tail ends, position regions such as the cerebellum, form specialised neurones and shape neural organisation.

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From the examiners' report: Give the brain as much space as the general roles: placing regions such as the cerebellum, and shaping neurones through mitosis and apoptosis. Long accounts of the lac operon or of conservation don't score.

Question 15

A level Paper 2 · June 2025 · Q16(c) · 6 marks · Medium

Using examples, explain the importance of mitosis and apoptosis in controlling the development of body form.

Six-mark level-of-response question: the development of body form begins in embryonic stem cells; using examples, explain the importance of mitosis and apoptosis as mechanisms controlling the development of body form.
Show the mark scheme Mark scheme indicative points: mitosis produces new cells for growth; apoptosis removes unwanted cells; both respond to internal and external stimuli under homeotic genes; examples such as digit separation and a tadpole losing its tail.

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From the examiners' report: Cover mitosis, apoptosis and examples separately (subheadings help), and give a clear example such as digit separation. Leave out the stages of mitosis.

Where students lose marks (from OCR examiners' reports and mark schemes)

Each point below is followed by wording that gained marks.

  • Introns leave the mRNA, not the DNA: Some students wrote about removing introns from DNA, used "extrons", or answered with the lac operon or histone modification.

    ✔ Gains credit: "Removal of introns" and "joining of exons" in the primary mRNA; "RNA editing".

  • Allele B acts through the protein it codes for: Many students wrote that "allele B turns off allele A", which gained no credit.

    ✔ Gains credit: "B codes for a repressor protein or transcription factor" that "binds to the promoter of A" and "stops transcription of A".

  • An inserted gene can disrupt its neighbours: Few students scored; many ignored "in that chromosome" and wrote about epistasis or meiosis.

    ✔ Gains credit: "Frameshift", "altered triplets", or "adjacent genes switched on or off".

  • A stop codon halts translation: Common errors were calling the change a frameshift or saying it caused early termination of transcription.

    ✔ Gains credit: "A shorter chain because an early stop codon has been introduced".

  • The genetic code is degenerate, not the bases: Many students called the amino acids, the bases or the DNA degenerate, and some gave a list of mutation types without linking them to protein structure.

    ✔ Gains credit: "The genetic code is degenerate", so "a silent mutation would leave the primary structure unchanged" and so the tertiary structure too.

  • Explain non-coding; don't just restate it: Many students described what non-coding might mean instead of explaining why those regions don't code for a polypeptide.

    ✔ Gains credit: "Introns are removed" so are "not present in mature mRNA" and "not translated".

  • Phagocytes tidy up after apoptosis: The usual wrong answers in the gaps were "hormonal", "conditions" and lysosomes, which were not credited.

    ✔ Gains credit: "Genetic and environmental control", "internal and external stimuli", and products "removed by phagocytes".

  • Hox genes in the brain need their own paragraph: Answers that didn't reach Level 3 were unbalanced, with most of the space on the general role of homeobox genes and little on the brain.

    ✔ Gains credit: "Expressed in a set order to determine regions of the brain" and "regulate mitosis and apoptosis of neurones".

Download the questions

Download the PDF pack (15 questions, mark schemes at the end)

Keep practising

Questions, mark schemes and examiners' report extracts © OCR.

Tom Whitburn
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