B3-Life On Earth

Adaptation and Variation

  • A species is a group of organisms that can breed together to produce fertile offspring.
  • Adaptations make individuals of a species more likely to survive an go on to produce offspring (so its more likely the species will continue to exist)

The Cactus:

  • Cacti have a rounded shape (giving them a small surface area compared to their volume) to reduce water loss
  • They have a thick waxy layer (called a cuticle) and spines to further reduce water loss.
  • They store water in their thick stem.
  • They have shallow but extensive roots (This allows water to be absorbed quickly)
  • Individuals of a species will usually look different. These differences are called variation. Some of this variation is cause by genes (so it can be passed on).
  • One of the causes of genetic variation is mutation. Mutations are caused by outside factors like radiation or chemicals. If mutations occur in body cells, they will have little or no effect but can lead to cancer. If they happen in sex cells, they can have a great effect as the mutation will then be passed to the offspring. This can cause offspring to develop new characteristics. Some of these will help survival, others will harm the organism.
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Natural Selection and Selective Breeding

  • Natural Selection is when certain organisms are better suited to the environment, they are more likely to survive and breed, passing on their characteristics to the next generation.
  • In this each species shows variation.
  • There is competition within each species for food, water, better living space and mates.
  • The "better adapted members" of the species are more likely to survive.
  • This is called 'SURVIVAL OF THE FITTEST'.
  • These survivors will pass on their better genes to their offspring who will also show these beneficial variations. 

Selective Breeding:

  • This is when parent organisms with certain characteristics are chosen to mate so that they can produce offsprimg the desired characteristics.
  • Selective breeding and natural selection both involve passing genes onto the next generation.
  • However, the main difference is that humans choose what animal should breed in selective breeding, but in natural selection humans aren't in charge of which animals breed.
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  • Biodiversity is a variety of living things in a habitat.
  • Biodiversity includes 1) a number of different species on earth, 2) a range of different types of organisms and 3) genetic variation between organisms of the same species. 

Maintainung Biodiversity is important because:

  • The more plants we have available, the more resources there are for developing food crops.
  • Some chemicals produced by living things are used in medicines. If a living organism becomes extinct, the unique chemicals it produces are no longer available.
  • Classification is when scientists use similarities and differences to put things into groups.
  • All species are classified into five different categories; bacteria, fungi, algae, plants and animals.
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Environmental Change


  • TEMPERATURE: Measured in the atmosphere to see if there is climate change/global warming.
  • NITRATE LEVELS: Measured to see how polluted water is. The more nitrate levels, the more polluted the water is. Increased nitrate levels is due to sewage and fertilisers entering into water.
  • CO2. Increased Carbon Dioxide levels is due to burning fossil fuels.


  • LICHENS: The less pollution, the more lichens are present. Lichens are found in tree bark and rocks.
  • MAYFLY NYMPHS: The less pollution, the more nymphs are present. Nymphs are sensitive to Oxygen.
  • PHYTOPLANKTON (ALGAE): The higher the levels of nitrates and phosphates in the water, the level of phytoplankton increases.
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The Carbon Cycle

1) In photosynthesis plants convert the carbon from Carbon Dioxide in the air into sugars.

2) Eating passes the carbon compunds in the plants along to animals in a food chain.

3) Plants and animals respire which releases carbon dioxide back into the air.

4) Plants and animals die and decompose.

5) When plants and animals decompose, they're broken down by micro-organisms. The decomposers release carbon dioxide back into the air by respiration.

6) The combustion of fossil fuels releases carbon dioxide into the air.

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The Nitrogen Cycle

1) Lightning splits Ninto N and N. Oxygen reacts with N to make NO (Nitrogen Oxide). NO comes into the soil.

2) NITROGEN-FIXING BACTERIA turn atmospheric nitrogen (N2) into nitrates that plants can use.

3) These bacteria live in soil and in Root Nodules (swellings on the roots of plants).

4) Animals eat plants.

5) Animals poo/pee the nitrates out.

6) Decomposers breakdown the poo/pee into ammonia.

7) Ammonia is broken down into nitrates by NITRIFYING BACTERIA.

8) DENITRIFYING BACTERIA converts nitrates in soil into atmospheric Ngas and sends it into the atmosphere.

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