Fossils

• All known living organisms on Earth are descended from a common ancestor
• DNA and fossils

  • Can be used to evidence common ancestry
  • The more similar an organism's DNA to another organism the more 'related' they are and the more recently they shared a common ancestor
  • Fossils are impressions of ancient organisms naturally preserved in stone and are formed over millions of years
  • Fossils help us understand the evolution of species and the development of biodiversity over time
• Radioactive decay

  The process where unstable nuclear isotopes break down into smaller nuclei
• Radioactive decay is random (we cannot say exactly when a nuclei will decay) and spontaneous (there is no event that prompts the nuclei to decay)
• Half-life

  The average time taken for half of the unstable nuclei in a sample to decay
• Half lives can range from fractions of a second to millions of years
• Activity


  The number of decays per second, measured in Becquerels (Bq)
• Plotting activity against time

  1. Gives a characteristic decay curve

  2. Initially the amount of radioactive isotopes decreases rapidly, before the rate of decrease slows
• Finding half-life from a decay curve

  1. Draw a horizontal line from the y-axis, originating at the point corresponding to half the initial activity

  2. Where the horizontal line meets the decay curve, draw a vertical line down to the x-axis

  3. The point where this line reaches the x-axis is the half-life
• Each half-life, the activity halves
• what can dna and fossils be used for?

  Used to evidence how all living organisms on earth descend from a common ancestor
• what is the carrying capacity affected by?(population curve)

  number of different things including access to resources such as food, space, predation and disease
• what is a carrying capacity?

  maximum amount of individuals the earth can support
• what happens when we get further from a star?

  space becomes colder
• how do plants make their own food?

  photosynthesis
• how does photosynthesis work?

  by transferring light and chemical energy into chemical energy.
• how many food chains rely on photosynthesis?

  nearly all
• is photosynthesis endothermic?


  yes
• photosynthesis word equation

  carbon dioxide + water -> glucose + oxygen