B3 - Life on Earth

OCR - Twenty First Century Science

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The variety of life


In a species the organisms can:

  • breed together
  • produce fertile offspring


Horse(One type of species) + Donkey (Another type of species)

= Mule (infertile)

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Theory of Evolution

Theory of Evolution

Charles Darwin explained how natural selection could produce evolution.

Darwin made many observations on the beaks of finches on his journey to the Galapagos Islands.

He thought that all the different finches could of evolved from just one species and their beaks had adapted to food available. Variation between individuals of a species is caused by both the environment and genes.

Only genetic information can be passed onto the next generation, so without genetic variation there would be no natural selection.

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Three things make genes change, or mutate:

  • Mistakes when copying chromosomes
  • ionizing radiation
  • some chemicals

If sex cell genes mutate, three things may happen:

  • the mutation may have no effect
  • The fertilized egg may not develop
  • the offspring may have a better chance of surviving and reproducing. Then the mutated gene passes on to the next generation and becomes more common.

Over many years and generations, new species have evolved.

This is the result of the effects of mutations, environmental change, and natural selection.

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Communication systems

We have two communication systems.

1.) Nervous system - fast responses

2.) Hormones - slower responses

Both of these systems help to keep a constant internal environment - this is called Homeostatis.

The Nervous system uses electrical impulses to transmit messages and respond to them quickly. In vertebrates, the nervous system is made of nerve cells (neurons). It is controlled by the central nervous system (the brain and spinal cord).

Hormones are chemicals that travel in the blood. They carry information over the body and bring about long-lasting responses. Hormones transmit messsages more slowly than nerves.

An example of Homeostatis is if you are too hot, the brain detects that the temperature of the blood flowing through is too high. It sends an electrical impulse through the nervous system to your sweat glands. You start to sweat more.

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Extinction is when species die out. When a plant or animal is at risk of extinction it is called an endangered species.

Things that may cause extinction are:

  • Changes in our environment such as global warming are putting plants and animals at risk
  • New species moving into a habitat can put another one at risk
  • Disease can wipe out whole populations
  • Going hungry can endanger animals, for example if the food supply is low and there are no alternatives then that animal may be a risk. It is beneficial to have more than one type of food to eat.

Sustainability - meeting the needs of people today without damaging Earth for people of the future.

Biodiversity - the variety of life on Earth

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