AQA GCSE Science & Additional Science

Biology 1 Topic 8

Hodder Education Revision Lessons

EvolutionEvolution

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AQA GCSE Science & Additional Science

Biology 1 Topic 8

Overview

• Particular genes or accidental changes in the genes of plants or animals may give them characteristics that enable them to survive better. Over time this may result in entirely new species.

• There are different theories of evolution. Darwin’s theory is the most widely accepted.

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AQA GCSE Science & Additional Science

Biology 1 Topic 8

Darwin

Darwin’s theory of evolution by natural selection states that all species of living things have evolved from simple life forms that first developed more than 3 billion years ago.This is a theory and because of the timescales involved it is unlikely to be ever proven.

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Do you believe Darwin’s theory?

AQA GCSE Science & Additional Science

Biology 1 Topic 8

Galapagos finches

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AQA GCSE Science & Additional Science

Biology 1 Topic 8

Darwin’s theory barriers

Many people refused to accept Darwin’s theory because:

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• it was in conflict with religious views that God had created the universe and all creatures in it

• there was insufficient evidence to support the theory — Darwin had developed his ideas from finches on the Galapagos Islands; little other research had taken place

• the mechanisms of inheritance and genes were not known

AQA GCSE Science & Additional Science

Biology 1 Topic 8

Other theories

Other theories, including that of Lamarck (working before Darwin), are based mainly on the idea that changes that occur in an organism during its lifetime can be inherited. We now know that, in the vast majority of cases, this type of inheritance cannot occur.

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AQA GCSE Science & Additional Science

Biology 1 Topic 8

Lamarck’s theory

Lamarck thought that herons had evolved long legs because they stretched their legs to stay dry, as shown.They would then pass on these acquired characteristics to the next generation.

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AQA GCSE Science & Additional Science

Biology 1 Topic 8

Classification

Evolution and patterns of change can be studied effectively only if organisms are carefully defined and their relationships understood.Living organisms are classified into:

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• animals• plants• microorganisms

What do these terms mean?

AQA GCSE Science & Additional Science

Biology 1 Topic 8

Natural selection — theory

Evolution occurs via the process of natural selection:

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• Individuals within a species may show a wide range of variation because of differences in their genes.

• Individuals with characteristics most suited to the environment are more likely to survive and breed successfully.

• Those genes responsible for the survival characteristics are then passed down to the next generation.

AQA GCSE Science & Additional Science

Biology 1 Topic 8

Natural selection — practice

Explain, using the theory of natural selection, what may happen in the following scenario:

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Giant tortoises live on an island and eat ground plants and the leaves of bushes. Genetic variation means that some tortoises have longer necks than others. Normally there is plenty of food to go round but one year there is a big drought and food is in short supply.

Why might future generations of tortoises have more individuals with longer necks?

AQA GCSE Science & Additional Science

Biology 1 Topic 8

Mutations 1

Mutations are random genetic alterations. They can cause an extreme change in the characteristics of an organism.If such a mutation is coupled with a change in the environment, there can be a relatively rapid change in that species.

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AQA GCSE Science & Additional Science

Biology 1 Topic 8

Mutations 2

One example of a mutation and a rapid change is the peppered moth. Explain it.

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