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Date	November 2020	Marks available	4	Reference code	20N.2.SL.TZ0.4
Level	Standard level	Paper	Paper 2	Time zone	TZ0 / no time zone
Command term	Explain	Question number	4	Adapted from	N/A

Question

Sketch the complementary strand to complete the section of a DNA diagram.

[3]

Define mutation.

[1]

b.i.

Explain how evolution by natural selection depends on mutations.

[4]

b.ii.

Markscheme

a. correct base sequence: T, G, A;

b. strand drawn anti-parallel;

c. correct shapes used;

Award [2 max] if bonds are not from the correct carbon or if the nucleotides are not joined.

change in genetic makeup/DNA/nucleotide/base sequence

b.i.

a. mutations cause variation among organisms of same species/population;

b. some variations/mutations make individual more suited to its environment/way of life;

c. individuals that are better adapted survive and produce offspring;

d. individuals pass on genetic characteristics/mutation/variation to offspring;

e. natural selection increases frequency of characteristics/alleles that make individuals better adapted;

b.ii.

Examiners report

In part (a) most could gain marks for the correct shapes and sequence but did not gain the third mark as it was not shown as antiparallel. Some lost marks as a 2MAX was awarded if the bonds were not from the correct carbons. In part (b) the definition of mutation was quite well known, and most gained some marks in the explanation. Weaker students just wrote about evolution without relating it to mutations as asked. They also tended to give unnecessary examples, involving finches and moths etc.

[N/A]

b.i.

[N/A]

b.ii.

Syllabus sections

Core » Topic 5: Evolution and biodiversity » 5.2 Natural selection

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Core » Topic 5: Evolution and biodiversity

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