evidence for process of evolution

Question 1

Evidence provided by the fossil record.

Answer 1

• Fossils of the simplest organisms such as bacteria and simple algae are found in the oldest rocks, whilst fossils of more complex organisms such as vertebrates are found in recent rocks. This supports evolutionary theory that simple life forms gradually evolved over a long time period into more complex ones.
• The sequence in which the organisms are found matches their ecological links to each other. For example, plant fossils before animal fossils, which is consistent with the fact that animals require plants to survive.
• By studying similarities in the anatomy of fossil organisms, scientists can show how closely related organisms have evolved from the same ancestor.
• Fossils allow relationships between extinct and living organisms to be investigated.

Question 2

why are fossil records incomplete?

Answer 2

• Soft-bodied organisms (no skeleton) decompose quickly without fossilisation.
• Sometimes the necessary conditions for fossilisation does not occur (requires specific temperature and pressure).
• Many fossils have been destroyed over time by earths movements (volcanoes, earthquakes etc).

Question 3

What is a homologous structure?

Answer 3

A structure that appears superficially different in different organisms, but has the same underlying structure.

Question 4

Comparative anatomy.

Answer 4

• Vertebrate limbs are used for a wide variety of functions such as running, jumping, and flying. Basic structures of all vertebrate limbs are very similar - the bones are adapted to carry out the whole range of different functions. An explanation is that all vertebrates have evolved from a common ancestor, therefore vertebrate limbs have all evolved from the same structure.
• Presence of homologous structures provide evidence for divergent evolution. This describes how from a common ancestor, different species have evolved, each with a different set of adaptive features.

Question 5

Comparative biochemistry

Answer 5

• This is the study of the biochemistry of molecules common to all living organisms e.g. RNA , DNA, Proteins.
• To study how closely related 2 species are the molecular sequence of a particular molecule can be compared e.g base sequence of the DNA or the amino acid sequence of a protein.
• molecules change over time due to chance mutations in the DNA - different bases are substituted for the normal ones in the sequence. These changes are often “neutral” - they don’t affect the function of the molecule, but they can give us an idea of how long ago 2 species diverged from each other.

Question 6

How to do DNA hybridisation:

Answer 6

• Take a sample of DNA from 2 organisms that you want to compare,
• Heat the DNA to convert it from the double stranded to single stranded (the hydrogen bonds between the 2 strands break)
• Mix the single stranded DNA from the 2 organisms together and give it time to see how well it hybridises.

Question 7

What does how well DNA molecule hybridise say about it?

Answer 7

• If the single stranded DNA molecules from the 2 organisms hybridises completely, they are the same species.
• If it hybridises partially, they are related to some degree.
• If it does not hybridise at all, they are not related.