Biology B4*

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Ecology in the Local Environment

Distribution of Organisms

  • An ecosystem is made up of all plants and animals living there and there surroundings
  • Where a plant or animal lives is called its habitat
  • All the plants and animals living in the garden make up the community
  • The number of a particular plant or animal living there is called its population
  • Natural ecosystem have a large variety of plants and animals living there - it has good biodiversity
  • Artificial ecosystems have poor biodiversity
  • The distribution of organisms can be mapped using a transect line
  • The data can be displayed as a kite diagram
  • In artificial ecosystems, humans deliberatley keep and protect one species and remove any other animals that would compete with it/lower the yeild
  • A trabsect line can show zonation on the distribution of organisms
  • Changes in abiotic (not biological) factors cause zonation
  • Food chains and food webs show that plants and animals are interdependant, with energy being transferred from one organism to another
  • The exchange of gases in photosynthesis and respiration ensures an overall balance of these gases
  • An ecosystem is self-supporting in all factors apart fom having to have the sun as an energy source

Population Size

  • Population size can be estimated by obtaining data from a small sample and scaling up
  • Population size = number in 1st sample x number in 2nd sample / number in 2nd sample previously marked


The chemistry of Photosynthesis

  • 6CO2 + 6H2O =  C6 H12 O6 + 6O2
  • The sugars in glucose can be: 1) used in respiration, releasing energy 2) converted into cellulose to make cell walls 3) converted into proteins for growth and repair 4) converted into starch, fats and oils for storage
  • Starch is used for storage because it is insoluble and does not move from storage areas. It does not affect water concentration and cause osmosis
  • Photosynthesis is a two stage process: 1) water is split up by light energy releasing oxygen gas and hydrogen ions. 2) carbon dioxide combines with the hydrogen ions producing glucose and water

Historical understanding of Photosynthesis

  • Greek scientists believed that plants took minerals out of the soil to grow and gain mass
  • Van Helmont concluded that plant growth could not be only due to the uptake of soil minerals
  • Priestly's experiment showed that plants produce oxygen
  • Modern experiments using an isotope of oxygen show that light energy is used to split water, not carbon dioxide

The Rate of Photosynthesis

  • It can be increased by the plant having : 1) more carbon dioxide. 2) more light. 3) a higher temperature which increases enzyme action
  • Photosynthesis will only take place in the daytime
  • Plants respire at all times by taking in oxygen and releasing carbon dioxide
  • During the day they also carry out photosynthesis, taking in carbon dioxide and releasing oxygen
  • The rate of photosynthesis is more that the rate of respiration
  • Photosynthesis depends on light, temperature and carbon dioxide, a lack of one of these factors will limit the rate of


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