AQA B2 2.8 Speciation

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  • Created by: Rchilds
  • Created on: 30-05-17 20:15
How do scientists gather evidence about early forms of life?
Fossils
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What is a fossil?
the ‘remains’ of organisms from many years ago, which are found in rocks
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How are fossils formed from hard parts of animals?
Dead animals are buried in sediment. Soft parts of animals decay away but harder parts e.g. bones and shells don't as easily. Over time, the hard parts may be replaced with minerals forming the fossil.
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How are fossils formed from casts like footprints, burrows and rootlet traces?
They get covered in layers of sediment which compress and turn into rock
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How can fossils be formed that also may preserve DNA?
Sometimes parts of organisms have not decayed because one or more of the conditions needed for decay are absent e.g. no oxygen, wrong temperature. This could be in tar pits, ice or insects in amber
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Why are there gaps in the fossil record?
conditions might not have been right for fossilisation, geological activity has destroyed fossils/has destroyed evidence, fossils not yet found
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Why are there very few fossils from early life?
Many early forms of life were soft-bodied, which means that they have left few traces behind. What traces there were have been mainly destroyed by geological activity.
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Why are fossils useful?
We can learn from fossils how much or how little different organisms have changed as life developed on Earth.
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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 some reasons for extinction?
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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What is a species?
A group of organisms that can interbreed and produce fertile offspring
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Explain the process of speciation (on 2 cards)
1. Populations isolated by geographical barrier/land/water. 2. There is genetic variation in each population/mutations occur. 3. There are different environment/conditions for each population
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speciation continued
4. Natural selection occurs on each population separately. 5. The favorable alleles / genes / mutations passed on in each population 6. eventually two types cannot interbreed successfully
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What are the conditions for speciation to occur?
Populations have to be isolated from each other for long periods of time so they cannot mate. The environments must be sufficiently different so that natural selection can take place differently on each population
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Recap of B1: describe the process of natural selection
In a species there is VARIATION. There is a change in the environment which means some characteristics are more successful than others. Organisms with these characteristics survive, breed and pass the successful GENES on. Organisms without it die out
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Other cards in this set

Card 2

Front

What is a fossil?

Back

the ‘remains’ of organisms from many years ago, which are found in rocks

Card 3

Front

How are fossils formed from hard parts of animals?

Back

Preview of the front of card 3

Card 4

Front

How are fossils formed from casts like footprints, burrows and rootlet traces?

Back

Preview of the front of card 4

Card 5

Front

How can fossils be formed that also may preserve DNA?

Back

Preview of the front of card 5
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