b3 life on earth

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  • Created by: ayaat
  • Created on: 13-05-13 15:38
  • . B3 Life on Earth
  • 2. Adaptations and VariationsA species is a group of organisms that can breedtogether to produce fertile offspringSpecies adapt to their environments• Adaptations make individuals of a species more likely to survive and go on to produce offspring- this makes it more likely that the whole species will continue exist in the environment E.G cactus- are adapted for hot, dry(desert conditions). They have small surface area to reduce water loss and shallow extensive roots to make sure water is absorbed quickly in a large area
  • 3. Individuals of the same species have differences• The differences are called variation within a species• Some variations are genetic- it can be passed on to the individual’s offspring• Causes of genetic variation is when the genes change- mutations• Mutations can be caused by outside factors, like radiation or chemical and my mistake when genes are copied during cell division• If mutations occur in body cells, they usually have little or no effect because the mutation will be passed on to all the cells of the offspring• This can cause offspring to develop new characteristics- might be harmful but others can help them to survive
  • 4. Darwin’s Natural Selection• Means the survival of the fittest• All living this show genetic variation• The resources living things need to survive are limited so there is competition for resources to survive- only some with survive• Some variety of species will have a better chance of survival therefore they have a greater chance of reproducing and passing on their genes• That means grater proportions of individuals in the next generation with have the characteristics that will help the organisms to survive• Over many generations species will become better and better at being able to survive.• The best features are naturally selected and the species become more adapted to their environments
  • 5. Selective Breeding• This is where humans choose what gets selected• This involves humans deliberately choosing a feature they what to appear in the next generation and only breeding animals or plants will have it• Unlike natural selection, selective breeding may promote features that don’t help survive but to benefit humans
  • 6. Evolution• The Earth is approximately 4.5 billion years old.• Life has been present for the last 3.5 billion years.• There are no records of when life began• We can only have theories:Life developed from molecules that like DNA, could copy themselves.Earth could have been very different and these molecules could have only been present on the planet then.Or these starter molecules many have been in rock from another planet.As the molecules joined they became more complex organisms.• The evidence for this are fossil records and DNA- scientists use similarities and differences
  • 7. Lamarcks theory• Characteristics used a lot by an animal would become more developed. These characteristics could be passed on to the animal’s offspring.
  • 8. The process of Evolution can produce new species• Sometimes groups of organisms of the same species can become isolated from each other so they can’t interbreed• Different…


lisa linsdell


Good coverage of OCR twentyfirst century B3 unit. Although difficult to read in some places. Use the 'test yourself' facility several times to ensure complete coverage of these revision notes.

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