Core Science B3 - Life on earth
- Created by: Sarah-Beth
- Created on: 14-06-12 10:48
B3 – Life on Earth
Evolution
· Life is varied
· Species vary from 2 million to 100 million
· Some have become extinct
· The first living things were simple
· Life then evolved to be more complex
· All species now evolved from the simple early ones
· There is good evidence for evolution
· Fossil records and DNA provide evidence
· Fossil records – shows species getting more complex
· DNA controls characteristics, changes over time
· Scientists use similarities and differences to discover how life has evolved
· Somehow life must have started
· Scientists estimate life began 3500 million years ago
· Religious groups that god created life
· Some believe it came from outer space, from a meteorite
· Most scientists – chemical was formed that could copy itself
· How this happened is uncertain
· Experiments show if you expose a mixture of the chemicals that were around, to an electrical charge, amino acids can form.
Natural Selection
· Natural selection is the process that causes evolution
· The resources living things need to survive are limited
· Must compete – only some will survive
· Some of the same species have better chances
· Which means more of a chance to breed and passing on genes
· So the greater proportion of individuals in the next generation will have the better alleles and so characteristics that help them survive
· Over generations, chances of survival increase
· The best features are naturally selected and the species becomes more adapted to its environment
· The best genes for a particular environment tend to survive
· Variations that are caused by the environment itself aren’t involved in natural selection
· Artificial selection is where humans choose what gets selected
· Deliberately selecting a feature they want to be in the next generation.
Producing new species
· Mutations happen when genes aren’t copied properly
· Over the years new features have appeared in animals and plants
· Caused by new genes that have been produced when existing genes change
· Changes are called mutations
· Happen all the time
· Mutations can be caused by outside factors like radiation or chemicals
· Also by mistakes when genes are copied in cell division
· Occur in body cells
· Usually have little or no effect but can cause cancer
· If they occur during the making of sex cells, they have more effect
· As the mutation will then be passed on to offspring
· These mutations have one of these results:
· - No effect – occur in an unimportant part of the DNA
· - Cause an essential chemical to be missing or create new characteristics –…
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