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Date May 2017 Marks available 2 Reference code 17M.2.SL.TZ1.4
Level Standard level Paper Paper 2 Time zone Time zone 1
Command term Explain Question number 4 Adapted from N/A

Question

The following cladogram shows three possible evolutionary routes for the turtle (Turtles 1, Turtles 2 and Turtles 3). The taxa in italics are extinct.

State the organism most closely related to the lizards.

[1]
a.i.

Based on the taxa shown, deduce a difficulty in gathering data to study turtle ancestry.

[1]
a.ii.

Molecular evidence is often used to construct a cladogram. Describe one type of molecular-based evidence to identify members of a clade.

[2]
b.i.

Suggest one type of additional evidence that could provide strong support for Turtles 3 as the evolutionary route for turtles rather than Turtles 1 or Turtles 2.

[1]
b.ii.

Taxonomists aim to place species into genera, families and higher taxa according to their evolutionary origins. This is known as natural classification.

Explain the usefulness of natural classification in biodiversity research.

[2]
c.

Markscheme

Tuatara

a.i.

some «taxa» are extinct
OR
convergence «of body form» could have occurred (confusing interpretation of the data)

a.ii.

a. base sequences of a gene/DNA/mtDNA
OR
amino acid sequences of a protein 

b. species with the most similarities «in base sequence/amino acid sequence/genomes» have recently diverged/a common ancestor/are closely related
OR
members of a clade accumulate the fewest mutations on same base sequences/ vice versa / OWTTE

b.i.

fossils / comparative anatomy / homologous structures / vestigial structures

b.ii.

a. «because» it allows easier identification of a species 

b. «because» it can help identify common ancestors/evolutionary paths/close relationships (showing degree of biodiversity) / OWTTE 

c. «because» it is universal/cross-cultural language that avoids problems of local names of organisms
OR
«because» it promotes international collaboration
OR
«because» it facilitates access to the history/background of the species /indexing for retrieval of relevant «taxonomic» information / OWTTE 

d. «because» it allows «biodiversity» research of larger taxa «ie examination of a family of large cats rather than one species»

c.

Examiners report

[N/A]
a.i.
[N/A]
a.ii.
[N/A]
b.i.
[N/A]
b.ii.
[N/A]
c.

Syllabus sections

Core » Topic 5: Evolution and biodiversity » 5.3 Classification of biodiversity
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