B3- Life on Earth

Adaption and variation

  • Species- A group of organisms that can breed together to produce fertile offspring.
  • Adaption makes individual species more likely to survive and go on to produce offspring.
  • Individuals of the same species have differences, these are variations and down to genetics. 
  • One of the cause of a genetic variation is gene changes, these are mutations.
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Natural selection

  • Survival of the fittest.
  • Selective breeding is where humans choose what gets selected. This is when humans deliberately choose a feature that they want, and then only breed from animals and plants that have it.
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Evolution

  • Life on Earth began about 3500 million years ago. The first living things were very simple, until they evolved to become more complex and varied.
  • Groups of organisms of the same species can become isolated from each other so they can't interbreed. This means different mutations can occur between to two groups causing variation between them.
  • Fossil records and DNA both provide evidence for evolution.
  • DNA mutates and change over time. All living things have similarities in their DNA as you would expect if they all evolved from the same simple life form.
  • Charles Darwin proposed the theory of evolution by natural selection
  • Lamarck argued however, that if a characteristic was used a lot by an animal then it would become developed and pass onto the offspring.
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Biodiversity and classification

  • Biodiversity includes; the number of species on earth, the range of different types of organisms and the genetic variation between organisms of the same species.
  • Maintaining biodiversity is important, and stopping animals becoming extinct is important because the more plants there is the more resources we have and the more chances of discovering new medicines.
  • The rate of extinction of species is increasing. 
  • Scientists group organisms together according to similarities in their characteristics, genetics, and physical features.
  • All species can be grouped into; Bacteria, Fungi, Algae, Plants, and Animals.
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Energy in an ecosystem

  • Every living thing needs resources from its environment. The essentials being; Light, food, oxygen/carbon dioxide, and water.
  • Nearly all the energy in an ecosystem comes from the sun.
  • Energy is transferred between organisms in an ecosystem when animals eat plants and other animals
  • However energy is lost at each stage as it is used for staying alive (respiration)
  • You hardly get food chains with more that five stages because so much energy is lost at each stage.
  • Efficency of energy transfer= energy available to the next stage/ energy that was available to the previous stage X 100
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The carbon cycle

  • The carbon cycle shows how carbon is recycled.
  • There is only one arrow going down. This is photosynthesis, plants taking in carbon dioxide.
  • Eating passes the carbon from plants into animals.
  • Both plants and animals respire, releasing carbon dioxide into the air.
  • When plants and animals die they are broke down by microorganisms that release carbon dioxide into the atomsphere.
  • The combustion of fossil fuels also release carbon dioxide into the air.
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The nitrogen cycle

  • The atomsphere contains 78% nitrogen gas (N2). This very unreactive and so can't be used directly by plants and animals.
  • Nitrogen is needed for making proteins for growth.
  • Nitrogen fixation is the process of turning nitrogen in the air into nitrogen compounds (e.g. nitrates)  in the soil which plants can use.
  • There is two main ways nitrogen fixation takes place; Lightning, it contains enough energy to make nitrogen react with oxygen. And nitrogen-fixing bacteria in roots and soil.
  • Decomposers break down proteins in dead plants and animals.
  • Urea is excreted in animal wasted and then broke down by decomposers into ammonia. Ammonia is turned into nitrates by nitrifying bacteria.
  • There are four tyoes of microorganisms involved in the cycle; decomposers, nitrifying bacteria, nitrogen-fixing bacteria, and denitrying bacteria.
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