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Date	May 2021	Marks available	1	Reference code	21M.2.SL.TZ1.5
Level	Standard level	Paper	Paper 2	Time zone	Time zone 1
Command term	Draw	Question number	5	Adapted from	N/A

Question

The image shows the wings of an insect, bird and bat.

[Source: [insect wing] Halvard Hatlen https://upload.wikimedia.org/wikipedia/commons/0/0f/Dip-trichoceridae-wing.png. [bird wing] University of Maryland, Department of Geology. [bat wing] University of Maryland, Department of Geology.]

Based on their structure, the insect and bat wings are analogous. Outline what is meant by an analogous trait.

[2]

a.i.

The bird and bat wings share homologous bone structures whereas the insect wing does not. Outline the conclusion that can be drawn about the evolution of these wings, based on homologous structures.

[1]

a.ii.

Explain how cladistics can be used to investigate evolutionary relationships.

[2]

Cladistics and other evolutionary evidence suggest that mammals and birds have a more recent common ancestor than mammals and amphibians. Draw a cladogram to show the relationships between mammals, birds and amphibians.

[1]

Markscheme

a. analogous traits have a different evolutionary history/ancestry ✔

b. different structures are adaptations for flight ✔

c. selective pressure leads to a similar solution to the problem of flying ✔

a.i.

a. bird and bat share a more recent common ancestor (than the insect) ✔

b. bird and bat are more closely related than insect and bat / insect and bird ✔

c. bird and bat wings evolved from a common ancestor (by natural selection) ✔

a.ii.

a. (cladistics) shows evolutionary relationships through a common ancestor ✔

b. cladistics uses DNA/protein/derived/shared anatomical characteristics/traits ✔

c. time of divergence is related to the number of differences in DNA (base sequence) / protein (sequence of amino acids) ✔

d. homologous (versus analogous) traits are used to place an organism in a clade ✔

e. more shared characteristics mean a more recent common ancestor ✔

What is important is that the proper relationships are shown not the style used.

Examiners report

Candidates found it hard to express themselves without contradiction.

In both parts the key to successful answers was in using the organisms given in the example. Contradictions were thus avoided.

a.i.

Candidates found it hard to express themselves without contradiction.

In both parts the key to successful answers was in using the organisms given in the example. Contradictions were thus avoided.

a.ii.

Candidates found it hard to express themselves without contradiction.

Carrying examples into part (b) made for the most successful answers. Very few gained marks for providing answers that included molecular level cladistic evidence, e.g. DNA, protein sequencing, etc.

Candidates found it hard to express themselves without contradiction.

Examiners accepted a wide variety of diagrams and orientations as long as the relationships among amphibians, birds and mammals were appropriate. Nevertheless, there was poor performance on this question. It was the question most often left blank in Section A.

Syllabus sections

Core » Topic 5: Evolution and biodiversity » 5.4 Cladistics

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