b2 speciation

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  • Created by: Avaaa
  • Created on: 21-03-17 17:54
summarise this topic
Changes in the environment of plants and animals may cause them to die out. The fossil record shows that new organisms arise, flourish, and after a time become extinct. The record also shows changes that lead to the formation of new species.
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■ suggest reasons why scientists cannot be certain about how life began on Earth.
The uncertainty arises from the lack of enough valid and reliable evidence.
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what are fossils
they provide evidence of early life forms.) Fossils are the ‘remains’ of organisms from many years ago, which are found in rocks. Fossils may be formed in various ways:
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in what ways... name two
from the hard parts of animals that do not decay easily ■ from parts of organisms that have not decayed because one or more of the conditions needed for decay are absent
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and the other two ways
■ when parts of the organism are replaced by other materials as they decay ■ as preserved traces of organisms, eg footprints, burrows and rootlet traces
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why arent all early forms of life oresent in fossils
) Many early forms of life were soft-bodied, which means that they have left few traces behind.
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what could have destroyed these traces
geological activity
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what can we learn from fossils
We can learn from fossils how much or how little different organisms have changed as life developed on Earth.
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what can extinction be caused by
changes to the environment over geological time ■ new predators ■ new diseases ■ new, more successful, competitors ■ a single catastrophic event, eg massive volcanic eruptions or collisions with asteroids ■ through the cyclical nature of speciation.
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why cant scientists be certain on how life began
• The first organisms were very simple single-celled organisms, similar to bacteria. • However, these rarely survive as fossils. • Therefore, Scientists cannot be certain about how life began on Earth. • It is only possible to develop theoretical mod
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theoritcal...
develop theoretical models that show how life may have started.
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so explain extinction
• If the organisms cannot evolve quick enough to become better adapted to the change they may become extinct.
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what happens if they do evolve
• If they do evolve, they are likely to develop into new species.
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what is a species
• A species is defined as a group of organisms that are capable of breeding together to produce fertile offspring. FERTILE
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New species arise as a result of
• Isolation – two populations of a species become separated, eg geographically. • Genetic variation – each population has a wide range of alleles that control their characteristics. •
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and the two other reasons..
■ natural selection – in each population, the alleles that control the characteristics which help the organism to survive are selected ■ speciation – the populations become so different that successful interbreeding is no longer possible
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Card 2

Front

■ suggest reasons why scientists cannot be certain about how life began on Earth.

Back

The uncertainty arises from the lack of enough valid and reliable evidence.

Card 3

Front

what are fossils

Back

Preview of the front of card 3

Card 4

Front

in what ways... name two

Back

Preview of the front of card 4

Card 5

Front

and the other two ways

Back

Preview of the front of card 5
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