B3 - Life On Earth

**Doesn't include B3.2, but includes the rest (.1, .3, .4)**

Revision cards for B3

Taken from a copy of the specification, I simplified and summarized them...

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  • Created by: emmy
  • Created on: 16-05-10 20:32

B3.1 - How did life on Earth begin and evolve?

- Life on earth began around 3,500 million years ago with small molecules that could copy themselves

- These molecules were produced by the conditions on earth at that time, or from elsewhere

- Evidence for evolution comes from fossils and DNA analysis

- Evolution happens due to natural selection

- Natural Selection: "Survival Of The Fittest"; genetic (mutations) and environmental variation between species means some are better adapted if there is competition, and therefore more likely to survive and breed, passing on genetic variations.

- Selective Breeding: Intentional breeding to produce offspring with desirable features to make money

- Combined effects of mutations, natural selection and environmental changes can produce new species.

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B3.3 - Human Evolution & Homeostasis

- The evolution of multicellular organisms has eventually led to nervous and hormonal communication systems

- Receptor cells (ie. eye pupil) detect stimuli (ie. a bright light) and effector cells (ie. iris muscles) produce a response (ie. the pupil becomes smaller)

- In vertebrates, the nervous system is co-ordinated by a Central Nervous System (the brain and spinal cord)

- Nervous System: electrical impulses; fast; short-lived responses.

- Hormones: chemicals; travel via the bloodstream; slow; long-lasting response.

- Some early humans developed a larger brain, giving them a better chance at survival

- Humans and primates evolved from a common ancestor; a species of hominids diverged; all but one of these became extinct (humans)

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B3.4 - Extinction

- Living organisms are dependent on the environment and other species for survival

- In the same habitat, different species of animals or plants have to compete for resources

- If one species in a food web becomes extinct, it can have an impact on other species

- Rapid change in the environment can cause a species to become extinct, ie: environmental conditions change; a new predator is introduced; disease.

- Extinction can be caused by direct human activity (ie. hunting) or indirect human activity

- Biodiveristy: The variety of life on earth

- The environment has to be used in a sustainable way so we can preserve it for future use and the development of crops and medicines

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benita marwaha

These were very very helpful. Thanks xo xo

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