IB Biology SL D1.1 DNA replication Questions

Practise IB Biology SL D1.1 by explaining replication steps and applying DNA principles to PCR, electrophoresis and profiling.

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

Syllabus
First assessment 2025
Course
Biology SL
Level
SL

Exam analysis

SL · 2010–2025
Papers with this topic40 / 141in the analysed sample
Latest appearanceNovember 2025
Tagged question parts50
Paper types5

Most tested objectives

  1. D1.1.4—PCR and gel electrophoresis19 papers
  2. D1.1.2—Semi-conservative replication11 papers
  3. D1.1.5—Applications7 papers
  4. D1.1.3—Role of helicase and DNA polymerase6 papers
  5. D1.1.1—DNA replication5 papers

Common question formats

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

Recent exam appearances

November 2025Paper 2 SL · TZ3Q2(b)[ 1 ]
November 2025Paper 1A SL · TZ3Q7[ 1 ]
May 2025Paper 2 SL · TZ3Q8(b)[ 4 ]

141 papers analysed · Tagging incomplete

Exam points

  • explain DNA replication before cell division using template strands, free nucleotides and complementary base pairing
  • identify one original and one newly synthesized strand and interpret Meselson–Stahl isotope-density evidence
  • distinguish helicase unwinding and hydrogen-bond breaking from DNA polymerase nucleotide addition
  • explain PCR amplification through denaturation, primer annealing and Taq-polymerase extension
  • interpret gel electrophoresis separation and DNA-profile band patterns by fragment size
  • apply PCR, fragment separation and band patterns to paternity or forensic conclusions

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—Applications

Exam points

  • Explain why DNA is replicated before mitosis so each daughter nucleus receives an identical DNA copy and genetic continuity is maintained.
  • Explain DNA replication using parent template strands, complementary base pairing and free nucleotides to form new strands.

Question 1

[Maximum number: 1]

Cisplatin is an anti-cancer drug that prevents tumour cells from dividing by mitosis as it inhibits cell processes at stage S of interphase. How does cisplatin prevent cancer cells from dividing?

A

It inhibits the replication of DNA.

B

It inhibits the growth of the spindle fibres.

C

It prevents the breakdown of the nuclear membrane.

D

It prevents the condensation of chromosomes.

Exam points

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

Question 1

[Maximum number: 1]

Which diagram(s) illustrate(s) semi-conservative replication of DNA?

Figure for Question 1 — IB Biology SL
A

X only

B

Y only

C

Z only

D

X and Y only

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: 1]

What bonds do the enzymes DNA polymerase and helicase form or break during DNA replication?

DNA polymerase

Helicase

forms sugar-phosphate bonds

breaks hydrogen bonds

forms hydrogen bonds

breaks sugar-phosphate bonds

forms hydrogen bonds

forms sugar-phosphate bonds

forms sugar-phosphate bonds

forms hydrogen bonds

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]

The diagram shows a gel electrophoresis apparatus.

Figure for Question 1 — IB Biology SL

What can be deduced from the diagram?

A

X is the smallest fragment.

B

Y is positively charged.

C

X is moving towards the cathode.

D

Y travels at the greatest rate.

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]

The diagram shows the DNA profile of two couples and two children.

Figure for Question 1 — IB Biology SL

What is the most probable relationship between them?

A

Couple X are the parents of both children.

B

Couple Y are the parents of both children.

C

Couple X are the parents of child 1 and couple Y are the parents of child 2 .

D

Couple X are the parents of child 2 and couple Y are the parents of child 1.