Question 1
Unit 4 style
A Level only (what this means)
A Level only: only in the full A Level, not the AS Level. AS Level students can skip it. What the labels meanExplain the role of saprotrophic bacteria and fungi in the recycling of carbon.
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Question 2
Unit 4 style
A Level only (what this means)
A Level only: only in the full A Level, not the AS Level. AS Level students can skip it. What the labels meanWhich step of the polymerase chain reaction takes place at about 72 °C?
- Denaturation of DNA
- Annealing of primers
- Extension of new strands by Taq polymerase
- Cutting of DNA by restriction enzymes
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Question 3
Unit 4 style
A Level only (what this means)
A Level only: only in the full A Level, not the AS Level. AS Level students can skip it. What the labels meanDescribe the stages in one cycle of the polymerase chain reaction.
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Question 4
Unit 4 style
A Level only (what this means)
A Level only: only in the full A Level, not the AS Level. AS Level students can skip it. What the labels meanCalculate the number of copies of a DNA sequence after 25 cycles of PCR, starting with a single molecule. Give your answer in standard form to two significant figures.
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Question 5
Unit 4 style
A Level only (what this means)
A Level only: only in the full A Level, not the AS Level. AS Level students can skip it. What the labels meanA sample of DNA was cut with a restriction enzyme and the fragments were separated by gel electrophoresis alongside a DNA ladder. The table shows the distance moved by the ladder bands. A band from the sample moved 33 mm. (a) Explain why the DNA fragments move through the gel and why shorter fragments move further. (2) (b) Use the table to estimate the length of the fragment in the sample. (2)
| Length of fragment / base pairs | Distance moved / mm |
|---|---|
| 5000 | 12 |
| 3000 | 20 |
| 2000 | 27 |
| 1000 | 38 |
| 500 | 47 |
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Question 6
Unit 4 style
A Level only (what this means)
A Level only: only in the full A Level, not the AS Level. AS Level students can skip it. What the labels meanDNA profiles were made from a mother, her child and two men, to find who might be the child's father. The table shows which bands were present (a tick shows a band at that position). (a) State which man could be the father and explain your answer. (2) (b) Explain why DNA profiling alone cannot prove that this man is the father. (2)
| Band position | Mother | Child | Man 1 | Man 2 |
|---|---|---|---|---|
| A | yes | yes | no | no |
| B | no | no | yes | no |
| C | yes | yes | no | no |
| D | no | yes | yes | no |
| E | yes | no | no | yes |
| F | no | yes | yes | no |
| G | no | no | no | yes |
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Question 7
Unit 4 style
A Level only (what this means)
A Level only: only in the full A Level, not the AS Level. AS Level students can skip it. What the labels meanDiscuss how a forensic scientist could use the body temperature, the degree of muscle contraction and the insects found on a dead mammal to estimate the time of death.
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Question 8
Unit 4 style
A Level only (what this means)
A Level only: only in the full A Level, not the AS Level. AS Level students can skip it. What the labels meanWhy do muscles become stiff (rigor mortis) after death?
- No ATP is available, so myosin heads stay attached to actin
- Calcium ions are no longer released, so actin and myosin are locked together
- Lactic acid denatures the muscle proteins
- Blood clotting prevents muscle fibres moving