plumiNucleic acids: OCR A‑Level Biology B questions
Every OCR A-Level Biology B exam question on 2.1.4 Nucleic acids, 2016–2025, with its mark scheme and examiner’s report.
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Q34(a)(iii)
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Q6(a)(i)
The whole paper ↗![June 2025 Paper 2, question 6(a)(i): Use data from the table for human, maize and E. coli DNA to explain the basis of Chargaff’s rules. [3]](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/h42202-jun25-06-ai-qp.webp?v=3)
Q6(a)(ii)
The whole paper ↗![June 2025 Paper 2, question 6(a)(ii): PhiX174 is a virus that has single-stranded DNA and does not obey Chargaff’s rules. Suggest an explanation for PhiX174 not obeying Chargaff’s rules. [1]](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/h42202-jun25-06-aii-qp.webp?v=3)
Q6(b)
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Q6(c)
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Q7(a)
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Q7(b)
The whole paper ↗![June 2025 Paper 2, question 7(b): A section of RNA is represented in the diagram. Draw a circle around a phosphodiester bond. Answer on the diagram. [1]](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/h42202-jun25-07-b-qp.webp?v=3)
Q7(c)
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Q22(a)(i)
The whole paper ↗![June 2025 AS Paper 1, question 22(a)(i): State the names of the types of bond labelled K and L. Bond K Bond L [1]](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/h02201-jun25-22-ai-qp.webp?v=3)
Q22(a)(ii)
The whole paper ↗![June 2025 AS Paper 1, question 22(a)(ii): State the function of the part of the molecule labelled M. [1]](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/h02201-jun25-22-aii-qp.webp?v=3)
Q22(a)(iii)
The whole paper ↗![June 2025 AS Paper 1, question 22(a)(iii): State the codon on the DNA antisense strand (template) that would result in this tRNA molecule attaching to mRNA during the process of translation. [1]](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/h02201-jun25-22-aiii-qp.webp?v=3)
Q22(b)
The whole paper ↗![June 2025 AS Paper 1, question 22(b): Compare the structure of a tRNA molecule to a molecule of DNA. [3]](https://pub-e8a9dbab8e2a4d089f52b2a45e0d0b50.r2.dev/bank/h02201-jun25-22-b-qp.webp?v=3)
Q22(c)
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Q22(d)
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Q1(a)
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Q1(b)
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All 73 questions on Nucleic acids, as a list
- June 2025, Paper 1, Q3 (1 mark): Which statement about ATP is not correct? A It can be hydrolysed to form AMP. B It contains the pentose sugar, ribose. C It contains the pyrimidine nitrogenous
- June 2025, Paper 1, Q4 (1 mark): The percentage base composition of DNA from a species of octopus is shown in the table. Base Adenine X Y Z % base composition 33.2 17.6 17.5 31.7 of DNA Which o
- June 2025, Paper 1, Q34(a)(iii) (3 marks): Spaceflight is thought to limit the production of RNA in cells. Explain how limiting RNA production may result in the change to myofibrils seen after spacefligh
- June 2025, Paper 2, Q6(a)(i) (3 marks): Use data from the table for human, maize and E. coli DNA to explain the basis of Chargaff’s rules. [3]
- June 2025, Paper 2, Q6(a)(ii) (1 mark): PhiX174 is a virus that has single-stranded DNA and does not obey Chargaff’s rules. Suggest an explanation for PhiX174 not obeying Chargaff’s rules. [1]
- June 2025, Paper 2, Q6(b) (3 marks): A group of students extract DNA from peas. This is the method they use: Blend 100 cm3 peas with 2 g table salt and 100 cm3 cold water. 1. 2. Strain through a me
- June 2025, Paper 2, Q6(c) (2 marks): One student places the ethanol in a water bath at 50 °C before using it in step 5. The student is unable to collect any DNA. The student carries out some resear
- June 2025, Paper 2, Q7(a) (3 marks): The table compares the structure of DNA and RNA nucleotides. Complete the table by writing the names of the structural features present in DNA and RNA. Structur
- June 2025, Paper 2, Q7(b) (1 mark): A section of RNA is represented in the diagram. Draw a circle around a phosphodiester bond. Answer on the diagram. [1]
- June 2025, Paper 2, Q7(c) (4 marks): Complete the following passage using the most appropriate words or phrases. Semi-conservative replication of DNA involves the enzyme , which breaks the bonds be
- June 2025, AS Paper 1, Q22(a)(i) (1 mark): State the names of the types of bond labelled K and L. Bond K Bond L [1]
- June 2025, AS Paper 1, Q22(a)(ii) (1 mark): State the function of the part of the molecule labelled M. [1]
- June 2025, AS Paper 1, Q22(a)(iii) (1 mark): State the codon on the DNA antisense strand (template) that would result in this tRNA molecule attaching to mRNA during the process of translation. [1]
- June 2025, AS Paper 1, Q22(b) (3 marks): Compare the structure of a tRNA molecule to a molecule of DNA. [3]
- June 2025, AS Paper 1, Q22(c) (2 marks): A group of scientists were investigating DNA replication and transcription in the bacterium Escherichia coli (E.coli). They found that: • DNA replication occurs
- June 2025, AS Paper 1, Q22(d) (3 marks): ATP is required to provide energy for DNA replication. Complete the sentences about the structure and function of ATP using the most appropriate word(s). ATP is
- June 2024, Paper 1, Q5 (1 mark): The following statement describes a feature of the genetic code: The same codon codes for the same amino acid in almost all species. Which feature of the geneti
- June 2024, Paper 3, Q1(a) (3 marks): ATP, DNA and tRNA are molecules that have some similarities but several differences in structure. The table lists structural features of ATP, DNA and tRNA. Use
- June 2024, Paper 3, Q1(b) (6 marks): (b)* Different methods are used to study DNA. Outline the methods you would use to: • purify DNA from plant tissue by precipitation • separate the DNA into frag
- June 2024, AS Paper 1, Q6 (1 mark): Which of the nucleotides would form a complementary base pair with an adenine-containing nucleotide in a DNA molecule? A B O O H3C NH NH O O O P N HO O O HO P O
- June 2024, AS Paper 1, Q7 (1 mark): Which option is a correct stage used in the purification of DNA from onion cells? A Add protease enzymes to break down the phospholipid bilayer of onion cells.
- June 2023, Paper 1, Q12 (1 mark): What bond joins adjacent nucleotides to form a polynucleotide chain? A Ester B Hydrogen C Ionic D Phosphodiester Your answer [1]
- June 2023, Paper 3, Q2(c)(ii) (2 marks): Genes responsible for NPQ and other aspects of photosynthesis in plants can be identified by sequencing and analysing DNA. DNA needs to be extracted and purifie
- June 2022, Paper 1, Q5 (1 mark): Which nitrogenous base pairs with adenine during DNA replication? A Cytosine B Guanine C Thymine D Uracil Your answer [1]
- June 2022, Paper 1, Q10 (1 mark): The reaction shows the breakdown of ATP to release energy. ATP ADP + Pi Which type of reaction is involved in the breakdown of ATP? A Condensation B Hydrolysis
- June 2022, Paper 2, Q2(a) (2 marks): The table lists structural features of DNA and transfer RNA (tRNA). Put a tick (3) in each box where that structural feature is present. The first row has been
- June 2022, Paper 2, Q2(b) (4 marks): Complete the sentences using the most appropriate terms. The first stage of protein synthesis is called , in which the enzyme DNA helicase unwinds the DNA so th
- June 2022, AS Paper 1, Q18 (1 mark): Molecules Y and Z are monomers that can be joined by a condensation reaction. Molecule Y Molecule Z NH2 O N N N NH O O N N HO P O HO P O N N NH2 O O OH OH HO OH
- June 2022, AS Paper 2, Q5(a) (1 mark): The table below shows an mRNA sequence and some of the amino acids coded for by that sequence. Complete the table with the correct amino acids. mRNA A U G G U G
- June 2022, AS Paper 2, Q5(b)(i) (2 marks): Each amino acid is coded for by a ‘triplet’ code. There are 64 different triplet combinations. Explain how this number is calculated. [2]
- June 2022, AS Paper 2, Q5(b)(ii) (2 marks): Only 20 different triplet combinations would be required to code for the 20 amino acids commonly found in living organisms. Explain what the remaining 44 combin
- June 2022, AS Paper 2, Q5(c) (2 marks): Selenocysteine is an unusual amino acid that is coded for by the codon UGA. It can be produced by Escherichia coli (E. coli ) when grown in the absence of sulfu
- November 2021, Paper 1, Q31(b)(i) (2 marks): Protamine contains large quantities of the polar amino acid, arginine. Suggest why having large quantities of arginine enables protamine to bind effectively to
- November 2021, Paper 1, Q35(a)(i) (1 mark): Messenger RNA (mRNA) [1]
- November 2021, Paper 1, Q35(a)(ii) (1 mark): Transfer RNA (tRNA) [1]
- November 2021, Paper 1, Q35(b) (4 marks): DNA is the nucleic acid that provides the genetic information required for protein synthesis. This information is known as the genetic code. Complete the passag
- November 2021, AS Paper 1, Q2 (1 mark): The diagram shows the process of translation that occurs during protein synthesis. Gly (Leu Ser Growing polypeptide chain (Asn) Gly Z TTA Ser) Ala) CGTCAA çuçuu
- November 2021, AS Paper 1, Q3 (1 mark): Tyrosine is an amino acid that can be coded for by two different DNA codons. Which of the options, A to D, is a feature of the genetic code that explains why th
- November 2021, AS Paper 1, Q4 (1 mark): Which of the options, A to D, are components found in a strand of ribonucleic acid (RNA)? A deoxyribose, uracil, phosphate B ribose, adenine, phosphate C ribose
- November 2020, Paper 1, Q11 (1 mark): Chromosome 1 in humans is composed of 2.5 × 109 base pairs. DNA polymerase has an error rate of 1 base per 108 bases. Which of the options, A to D, is the theor
- November 2020, Paper 2, Q1(a)(i) (2 marks): Give two ways, apart from size, in which mtDNA differs from nuclear DNA. 1. 2. [2]
- November 2020, Paper 2, Q1(a)(ii) (3 marks): Complete the following table of comparisons between mtDNA, RNA and ATP. Put a tick (3) in each box where that component is present. The first line has been comp
- November 2020, Paper 2, Q1(a)(iii) (1 mark): The mitochondrial genome contains 37 genes. Of these, only 13 code for proteins. Suggest what the remaining genes encode. [1]
- November 2020, Paper 2, Q1(b)(i) (2 marks): Explain what is meant by the term semi-conservative replication. [2]
- November 2020, Paper 2, Q1(b)(ii) (2 marks): Explain how mutations in the catalytic and exonuclease regions of the POLG gene could have different effects on the replication of mtDNA. [2]
- November 2020, AS Paper 1, Q7 (1 mark): Which of the molecules, A to D, is not involved in transcription? A mRNA B DNA C tRNA D RNA polymerase Your answer [1]
- November 2020, AS Paper 1, Q16 (1 mark): ATP contains three phosphate groups, a nitrogenous base and a pentose sugar. Which of the rows, A to D, is correct for ATP? Nitrogenous base Pentose sugar A ade
- November 2020, AS Paper 2, Q1(a)(i) (1 mark): Name the bonds found in the region labelled M on Fig. 1.1. [1]
- November 2020, AS Paper 2, Q1(a)(ii) (1 mark): Name the two components of DNA found in the region labelled N on Fig. 1.1. [1]
- November 2020, AS Paper 2, Q1(b) (2 marks): Fig. 1.2 shows nucleotide X. CH3 O– N S O O P O O– OH Fig. 1.2 Give two differences between the structures of nucleotide X and adenosine triphosphate (ATP). 1 2
- November 2020, AS Paper 2, Q1(c) (2 marks): The percentage of each nucleotide base in a DNA sequence can be estimated. Complete the table using Chargaff’s rule of DNA replication. Nucleotide Percentage of
- November 2020, AS Paper 2, Q1(d) (4 marks): Scientists have also been trialling cancer treatment drugs that form strong ‘crosslinks’ between the DNA strands. This is shown in Fig. 1.3. A T crosslink C G G
- November 2020, AS Paper 2, Q1(e) (4 marks): A student wanted to investigate the DNA content of two samples of plant tissue using the ethanol precipitation method in a school laboratory. They used the foll
- June 2019, Paper 1, Q5 (1 mark): The diagram below shows the structure of a nucleotide. A bond is labelled X. O N O NH HO P O N N NH2 O OH H H X OH H Which of the following statements is/are co
- June 2019, Paper 1, Q23 (1 mark): Which of the following statements about DNA replication in eukaryotes is/are correct? 1 Helicase exposes the templates required by DNA polymerase. 2 Free nucleo
- June 2019, Paper 2, Q1(e) (4 marks): In MGUS, B cells produce an abnormal polypeptide called M protein. Production of M protein involves the processes of transcription and translation. Complete the
- June 2019, AS Paper 1, Q22(c) (5 marks): Evidence from fossils and biochemical molecules, such as DNA, has enabled scientists to classify hominids. Complete the following passage about DNA using the mo
- June 2018, Paper 1, Q2 (1 mark): A student is purifying DNA from a bacterial culture. Which of the molecules, A to D, is required for the precipitation of DNA during the purification process? A
- June 2018, AS Paper 1, Q4 (1 mark): During the semi-conservative replication of DNA, which of the enzymes, A to D, is required to break hydrogen bonds between the nitrogen-containing bases? A DNA
- June 2018, AS Paper 1, Q22(a)(ii) (1 mark): Tetrahydrofolate is essential in subsequent reactions that synthesise purine nucleotides. Name two purine nucleotides. 1 2 [1]
- June 2018, AS Paper 1, Q22(a)(iii) (2 marks): Explain why methotrexate will eventually cause the death of the fertilised egg cell in an ectopic pregnancy. [2]
- June 2017, Paper 2, Q4(a)(i) (3 marks): Identify the parts of the DNA molecule labelled A to C in Fig. 4. A B C [3]
- June 2017, Paper 2, Q4(a)(ii) (2 marks): The table below shows the results of an analysis of the base composition for each strand of a DNA molecule. Complete the table by adding the missing values for
- June 2017, Paper 2, Q4(b) (2 marks): Hydrogen bonding is central to the function of nucleic acids. Explain how hydrogen bonding contributes to the process of semi-conservative replication of DNA. [
- June 2017, AS Paper 1, Q21(a)(i) (1 mark): can form a phosphodiester bond with other nucleotides? [1]
- June 2017, AS Paper 1, Q21(a)(ii) (1 mark): can join with phosphate groups to form ATP? [1]
- June 2017, AS Paper 1, Q21(a)(iii) (1 mark): can form hydrogen bonds with another nucleotide? [1]
- June 2017, AS Paper 1, Q21(b) (1 mark): Describe how a nucleotide found in deoxyribonucleic acid would differ from the nucleotide shown in Fig. 21. [1]
- June 2017, AS Paper 1, Q21(c) (4 marks): The sequence of nucleotides in DNA provides the genetic code for synthesising proteins. The genetic code can be described as universal because it is the same in
- June 2017, AS Paper 1, Q21(d)(i) (1 mark): What feature of the DNA molecule provides stability? [1]
- June 2017, AS Paper 1, Q21(d)(ii) (1 mark): Messenger RNA (mRNA) is the type of nucleic acid that carries the genetic information on DNA from the nucleus to the site of protein synthesis. Unlike DNA, mRNA
- June 2016, AS Paper 1, Q18 (1 mark): The table below compares the structures of mRNA and DNA. Strands Bases Sugar DNA 2 ATCG deoxyribose mRNA Which of the options, A to D, correctly completes the t
- June 2016, AS Paper 2, Q2(d) (6 marks): A group of students were investigating the protein content of a sports drink used by athletes. (d)* Proteases in the small intestine of an athlete will break do
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