B3 Life On Earth Summary

  • How life on Earth began
  • How creatures have evolved over time
  • Evolution by natural selection
  • Selective breeding
  • Nervous and communication systems
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The interdependence of living things

- A food web can show which organisms eat other organisms in a particular habbitat.

- Different species in a particular habitat often compete for the same space or food source.

- A change which affects one species in a food web also affects other species in the same food web.

- Ecosystems can often adjust to changes but large disruptions may change an ecosystem permanently.

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Maintenance of life

- Organisms need water, food and light to survive.

- Organisms need to avoid harmful chemicals, predators ad extreme temperatures in order to survive.

- They are more likely to survive if they can sense what they need, or need to avoid, in their surroundings.

- Multi - cellular organisms have sensor cells and effector cells.

- Multi - cellular animals have nervous systems.

- Nervous systems are comprised of nerve cells (neuron) which link sensor cells to effector cells.

- In humans they are linked via the central nervous system ( spinal cord and brain)

- Hormones are chemicals which travel in the blood and bring about slower longer - lasting responses.

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Theory of evolution by natural selection

- The first living things developed about 3.500 million years ago from molecules that could copy themselves.

- The molecules were produced in conditions on Earth at the time.

- Evolution occurs due to natural selection.

- If conditions on Earth had been different from what they were, natural selection could have produced very different results.

- There is variation between individuals of the same species.

- Individuals with certain characteristics have a better chance of surviving, and reproducing, if the environment changes or vital resources become scarce.

- There will be more individuals with these characteristics in the next generation and so on.

-Selective breeding involves making deliberate selections based on desirable charecteristics.

- New species have evolved over a very long period of time.

- A large change in the environment may cause an entire species to become extinct.

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Scientific explanations

- For some scientific questions, there is not a definite answer yet.

- An observation that agrees with a theory increases confidence in it.

- An observation that disagrees with a theory indicates that either the observation or the theory is wrong.

- Explanations cannot simply be deduced from the available data - personal background, experience or interests may influence judgements.

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Higher Teir

- Nervous and hormonal communication systems are involved in maintaining a constant internal environment (homoeostasis).

- Genes can be changes by mutation.

- Mutation can cause cancer cells.

- Mutated genes in sex cells can be passed onto offspring and produce new charecteristics.

- A new species can be produced by the combined effects of mutations, environmental changes and natural selection.

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