IB Biology HL D1.1 DNA replication Questions

Practise IB Biology HL D1.1 by explaining replication enzymes, strand directionality and applying DNA principles to PCR, electrophoresis and profiling.

92 questions in this syllabus scope, with question parts counted together.

Syllabus
First assessment 2025
Course
Biology HL
Level
HL

Exam analysis

HL · 2010–2025
Papers with this topic38 / 117in the analysed sample
Latest appearanceNovember 2025
Tagged question parts52
Paper types5

Most tested objectives

  1. D1.1.8 (HL)—Functions in replication14 papers
  2. D1.1.4—PCR and gel electrophoresis12 papers
  3. D1.1.5—Applications8 papers
  4. D1.1.1—DNA replication3 papers
  5. D1.1.3—Role of helicase and DNA polymerase3 papers

Common question formats

  • Definition or recall
  • Diagram interpretation
  • Structured response
  • Process explanation
  • Calculation
  • Data analysis
  • Comparison

Recent exam appearances

November 2025Paper 2 HL · TZ1Q9(a)[ 4 ]
November 2025Paper 1A HL · TZ3Q10[ 1 ]
November 2025Paper 1A HL · TZ1Q9[ 1 ]

117 papers analysed · Tagging incomplete

Exam points

  • explain semi-conservative replication using template strands, complementary pairing and one original plus one new strand
  • interpret Meselson–Stahl isotope-density patterns and contrast semi-conservative with conservative replication
  • distinguish helicase unwinding from DNA polymerase nucleotide addition
  • trace 5′ to 3′ synthesis and identify phosphodiester linkage formation
  • distinguish continuous leading-strand from discontinuous lagging-strand synthesis with Okazaki fragments and RNA primers
  • explain primase, DNA polymerase III, DNA polymerase I and ligase functions in replication
  • explain DNA polymerase III proofreading of mismatches and its effect on mutation rate
  • explain PCR amplification through denaturation, primer annealing and Taq-polymerase extension
  • interpret gel electrophoresis separation and DNA-analysis band evidence
  • analyse STR or DNA-profile patterns for paternity or forensic conclusions
  • outline medical applications of PCR including viral-strain identification, genetic testing, tissue typing or vaccine development

Covered syllabus points

D1.1.1—DNA replicationD1.1.2—Semi-conservative replicationD1.1.3—Role of helicase and DNA polymeraseD1.1.4—PCR and gel electrophoresisD1.1.5—ApplicationsD1.1.6 (HL)—DNA polymerase directionalityD1.1.7 (HL)—Leading vs. lagging strandD1.1.8 (HL)—Functions in replicationD1.1.9 (HL)—DNA proofreading

Exam points

  • Explain semiconservative DNA replication before cell division, using each parental strand as a template for a complementary daughter strand.

Question 1

[Maximum number: 1]

What is required to replicate DNA?

A

Temperature of 37∘C37^{\circ} \mathrm{C}

B

Free nucleotides carrying A, C, G and T bases

C

Plasmids

D

Endonuclease

Exam points

  • Explain that each daughter DNA molecule contains one original strand and one newly synthesized strand.
  • Use complementary base pairing on template strands to explain accurate DNA copying.
  • Use Meselson–Stahl isotope results to distinguish semi-conservative replication from the conservative model.

Question 1

[Maximum number: 1]

How is the sequence of DNA conserved?

A

Unwinding of the double helix by helicase during DNA replication

B

Separation of sister chromatids to opposite poles during mitosis

C

Transcription into complementary RNA for protein synthesis

D

Complementary base pair matching during DNA replication

Exam points

  • Explain how helicase unwinds DNA by breaking hydrogen bonds between the two strands.
  • Explain how DNA polymerase joins complementary nucleotides to build new DNA strands.

Question 1

[Maximum number: 4]

Cellular processes at the molecular level are regulated by enzymes.

Outline the role of DNA polymerase III in DNA replication.

Exam points

  • Explain how primers, temperature cycles and Taq polymerase allow PCR to amplify selected DNA.
  • Explain how gel electrophoresis separates DNA fragments by size and charge.

Question 1

[Maximum number: 1]

DNA fragments can be amplified by the polymerase chain reaction (PCR) to obtain many identical copies that can be used in forensic investigations.

What is a function of primers in PCR?

A

To form hydrogen bonds between complementary bases

B

To proofread the newly synthesized DNA copies

C

To keep double-stranded DNA fragments separated

D

To identify the regions of DNA that need to be replicated

Exam points

  • Describe how PCR and gel electrophoresis support DNA profiling for forensic identification.
  • Apply DNA-profile band patterns to assess a forensic match or paternity.

Question 1

[Maximum number: 1]

In DNA profiling, short tandem repeats (STRs) of DNA are used, as these vary a great deal between individuals. Some skin cells were retrieved from a crime scene. Three STR sections of the DNA from these cells, from the victim and from a suspect, were analysed and the results are shown in the table.

Table for Question 1 — IB Biology HL

What can be concluded from the gel electrophoresis data?

A

The suspect was at the crime scene.

B

The victim has the band moving the least distance.

C

The suspect and the victim have bands moving the same distance.

D

The skin cells have the band moving the greatest distance.

Exam points

  • Identify the 5′ and 3′ ends of DNA strands and state that DNA polymerase extends a new strand from its 3′ end, synthesizing DNA 5′ to 3′.

Question 1

[Maximum number: 1]

How does DNA replicate?

A

The deoxyribose of a free nucleotide is linked to the phosphate of the last nucleotide in the chain.

B

The phosphate of a free nucleotide is linked to the deoxyribose of the last nucleotide in the chain.

C

Nucleotides are linked in a 3′3^{\prime} to 5′5^{\prime} direction and the new strands are anti-parallel to the template strands.

D

Nucleotides are linked in a 5′5^{\prime} to 3′3^{\prime} direction and the new strands are parallel to the template strands.

Exam points

  • Identify that the lagging strand uses repeated RNA primers to form Okazaki fragments.

Question 1

[Maximum number: 1]

The image shows a replication fork.

Figure for Question 1 — IB Biology HL

Which row identifies X, Y and Z in the diagram?

X

Y

Z

5' end

DNA leading strand

5' end

3' end

Okazaki fragment

3' end

3' end

DNA leading strand

5' end

5' end

Okazaki fragment

3' end

Exam points

  • Explain how primase adds an RNA primer, DNA polymerase III extends new DNA, and DNA polymerase I replaces RNA primers with DNA.
  • Explain how DNA ligase joins Okazaki fragments.

Question 1

[Maximum number: 1]

What is the function of DNA polymerase I in DNA replication?

A

It forms primers by adding short lengths of RNA to the template strand.

B

It removes RNA primers and replaces them with DNA.

C

It builds the leading strand by adding DNA nucleotides continuously.

D

It forms Okazaki fragments by adding DNA nucleotides on the lagging strand.

Exam points

  • Identify DNA polymerase III as the proofreading enzyme during DNA replication.
  • Explain how DNA polymerase III removes a mismatched nucleotide from the 3′ end, improving copying accuracy and reducing mutations.

Question 1

[Maximum number: 1]

Which enzyme is associated with proofreading during DNA replication?

A

DNA primase

B

DNA helicase

C

DNA polymerase III

D

DNA ligase

Question 1

[Maximum number: 8]

Cellular processes at the molecular level are regulated by enzymes.

Question (a)

(a)

Outline the process of DNA profiling.

[ 4 ]

Question (b)

(b)

Outline the role of DNA polymerase III in DNA replication.

[ 4 ]
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