Core Science B3 - Life on earth

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 –…