D1.1 DNA replication questions for IB Biology
41 questions on DNA replication, written by Augment in the style of IB exam papers. Six of them are below in full, to answer on paper.
- IB Biology
- Part of D Continuity and change
- SL and HL
Questions by paper and level
SL and HL questions are for students at either level. HL only questions cover what only HL students study.
| Paper | SL and HL | HL only | All |
|---|---|---|---|
| Paper 1A | 12 | 8 | 20 |
| Paper 1B | 3 | 2 | 5 |
| Paper 2 | 10 | 6 | 16 |
| Every paper | 25 | 16 | 41 |
Counted on
Questions to try
Written by Augment in the style of IB exams, not past papers. Answer them on paper, then check each one against its markscheme with a free account.
Which process in a multicellular organism depends on DNA replication?
Three hypotheses were proposed for DNA replication. In conservative replication, the original molecule stays intact and a completely new molecule is made. In semi-conservative replication, each new molecule contains one original strand and one new strand. In dispersive replication, every strand is a mixture of original and new sections, so all molecules have the same density, which falls with each generation.
To test these hypotheses, bacteria (Escherichia coli) were grown for many generations in a medium in which the only source of nitrogen contained the heavy isotope 15N. They were then transferred to a medium containing only the normal isotope 14N. Samples were taken each time the population doubled (one generation), the DNA was extracted and it was centrifuged in a dense salt solution, which separates DNA molecules into bands according to their density. The table shows the percentage of the DNA found in each band.
Generations after transfer to 14N | Heavy DNA (15N only) / % | Intermediate (hybrid) DNA / % | Light DNA (14N only) / % |
|---|---|---|---|
0 | 100 | 0 | 0 |
1 | 2 | 98 | 0 |
2 | 0 | 51 | 49 |
3 | 0 | 26 | 74 |
4 | 0 | 12 | 88 |
- (a)
State which part of a DNA nucleotide contains the nitrogen that was labelled.
1 mark
- (b)
Suggest why the bacteria were grown for many generations in the 15N medium before the transfer.
1 mark
- (c)
Explain how the results after one generation show that replication is not conservative.
2 marks
- (d)
Explain how the results after two generations allow dispersive replication to be rejected.
2 marks
- (e)
Calculate the percentage of DNA that would be expected to be intermediate (hybrid) after four generations if replication is semi-conservative.
1 mark
- (f)
Outline the role of complementary base pairing in semi-conservative replication.
2 marks
Nucleic acids store genetic information and allow it to be copied and expressed.
- (a)
Draw a labelled diagram of a section of a DNA molecule consisting of two nucleotides on each strand.
4 marks
- (b)
Explain how the base sequence of a gene is used to produce a polypeptide.
7 marks
- (c)
Outline the roles of helicase and DNA polymerase in DNA replication.
4 marks
Which row describes the roles of helicase and DNA polymerase in DNA replication?
Row | Helicase | DNA polymerase |
|---|---|---|
A | unwinds the double helix and breaks hydrogen bonds between the two strands | links nucleotides together to form a new strand complementary to the template |
B | links nucleotides together to form a new strand complementary to the template | unwinds the double helix and breaks hydrogen bonds between the two strands |
C | unwinds the double helix and breaks covalent bonds within each strand | links nucleotides together to form a new strand complementary to the template |
D | unwinds the double helix and breaks hydrogen bonds between the two strands | forms hydrogen bonds that rejoin the two original strands |
The polymerase chain reaction (PCR) was used to amplify a 500 bp sequence of DNA. Thirty identical reaction tubes were set up and placed in a thermal cycler. After 10, 15, 20, 25, 30 and 35 cycles, five tubes were removed and the mass of DNA product in each was measured using a fluorescent dye that binds to double-stranded DNA. The table shows the mean mass and the standard deviation.
Number of cycles | Mean mass of DNA product / ng | Standard deviation / ng |
|---|---|---|
10 | 0.6 | 0.1 |
15 | 17 | 2 |
20 | 380 | 35 |
25 | 1450 | 120 |
30 | 1780 | 150 |
35 | 1820 | 160 |
- (a)
State the independent variable in this investigation.
1 mark
- (b)
Calculate how many times the mass of DNA product increased between 10 and 15 cycles, and compare this with the increase expected if the number of DNA molecules doubled in every cycle.
2 marks
- (c)
Describe the trend in the mass of DNA product between 10 and 35 cycles.
2 marks
- (d)
Using the standard deviations, deduce whether the difference in mean mass between 30 and 35 cycles is likely to be significant.
1 mark
- (e)
Suggest one reason why the mass of DNA product levels off after many cycles.
1 mark
- (f)
Explain why the number of DNA molecules approximately doubles in each cycle of PCR.
3 marks
Genetic information varies between individuals and between species.
- (a)
Outline what single-nucleotide polymorphisms (SNPs) are and how they arise.
4 marks
- (b)
Describe how the polymerase chain reaction (PCR) and gel electrophoresis can be used to amplify and separate DNA.
4 marks
- (c)
Explain the current and potential future uses of whole genome sequencing, and why these uses are becoming more widespread.
7 marks
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More questions in Continuity and change
- D1.1DNA replicationThis page
- D1.2Protein synthesis
- D1.3Mutations and gene editing
- D2.1Cell and nuclear division
- D2.2Gene expressionHL only
- D2.3Water potential
- D3.1Reproduction
- D3.2Inheritance
- D3.3Homeostasis
- D4.1Natural selection
- D4.2Stability and change
- D4.3Climate change
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