What is a pentadactyl limb?

It is a limb built from the same basic arrangement of bones and ending in five digits.

Explain why the pentadactyl limb is treated as evidence for evolution.

The same bones appear in the same order in limbs used for completely different jobs, which is best explained by all these species inheriting the limb from a shared ancestor.

Explain why unrelated species would not be expected to share the pentadactyl bone arrangement.

If each limb had arisen separately purely to suit its own function, there would be no reason for them all to use the same bones in the same pattern.

Edexcel GCSE Biology 1BI0

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Natural Selection and Genetic Modification

Topic overview Darwin, Wallace and the theory of evolution Natural selection and antibiotic resistance Fossil evidence for human evolution Stone tool evidence for human evolution The pentadactyl limb and the three domains Selective breeding Tissue culture Genetic engineering and modern agriculture Benefits and risks of GM organisms

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Natural Selection and Genetic Modification

The pentadactyl limb and the three domains

3 things to know
Paper 1

Overview

The pentadactyl limb, the vertebrate groups that share it and how it is modified in a bat's wing and a whale's flipper, why it is evidence for a shared ancestor, the older five kingdom system, and Carl Woese's three domains of Archaea, Bacteria and Eukarya based on genetic analysis.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Name the groups of vertebrates whose limbs share the pentadactyl arrangement.

Key term

Give three very different limbs that are all built on the pentadactyl plan.

Key term

Describe how the pentadactyl limb of a bat has been modified compared with that of a human.

Questions from this subtopic

Each one with the model answer underneath.

1
What is a pentadactyl limb?
Model answer
It is a limb built from the same basic arrangement of bones and ending in five digits.
2
Name the groups of vertebrates whose limbs share the pentadactyl arrangement.
Model answer
Amphibians, reptiles, birds and mammals.
3
Give three very different limbs that are all built on the pentadactyl plan.
Model answer
A human arm, a bat's wing and a whale's flipper.
4
Explain why the pentadactyl limb is treated as evidence for evolution.
Model answer
The same bones appear in the same order in limbs used for completely different jobs, which is best explained by all these species inheriting the limb from a shared ancestor.
5
Explain why unrelated species would not be expected to share the pentadactyl bone arrangement.
Model answer
If each limb had arisen separately purely to suit its own function, there would be no reason for them all to use the same bones in the same pattern.
6
Describe how the pentadactyl limb of a bat has been modified compared with that of a human.
Model answer
The finger bones are enormously lengthened and support a thin skin membrane that forms the wing.

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