AQA unit 4 biology notes

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  • Created by: Ryan
  • Created on: 15-01-12 15:48


  • Population - A group of organisms from the same species who are living together at the same time in the same place that if reproducing sexually can interbreed.
  • Community - All the populations of different species living together in one area at the same time.
  • Habitat - The place where a organism species, population or community is living.
  • Ecosystem - All the communities as well as non-living parts of an area together make up an ecosystem.
  • Biosphere - All of earth’s ecosystems together make one large ecosystem known as the biosphere.
  • Producers - Plants and some photosynthetic bacteria who transfer energy from the sunlight into organic compounds which in most cases take the form of carbohydrates.
  • Consumers - All organisms who consume the energy created by the producers either directly or indirectly.
  • Productivity - The amount of energy in each organism in each trophic level over a set period of time.

Food Webs/Chains

Food webs and food chains are a method of diagrammatically showing how energy flows within and ecosystem. Food webs can be divided into trophic levels, the first trophic level contains the producers, the second has the herbivores and the third has the carnivores. Animals can belong in different trophic levels. The forth group of organisms are called decomposers, these feed on dead bodies from the other organisms in the ecosystem.

Pyramids of biomass, numbers and energy

These pyramids are graphical representations of either the number of organisms, the amount of biomass or energy within and ecosystem and how they flow. This is done by dividing the organism into different trophic levels. Drawing an energy pyramid shows how energy is lost as you pass up the trophic levels as a result of energy used in movement, digestion, metabolic processes, also inefficient digestion means that much of the potential energy that is ingested gets excreted. Respiration There are two forms of Respiration; Aerobic and Anaerobic. Aerobic Respiration needs Oxygen and produces Carbon Dioxide, Water and ATP. 32 molecules of ATP are produced per Glucose molecule. Anaerobic Respiration (also known as fermentation) takes place when Oxygen is absent. In this case Oxygen, Lactate (animals) or Ethanol (plants) and very few molecules of ATP are produced.   2.     Stages of Respiration 1)    Glycolysis – the splitting of a 6-carbon glucose molecule into 2 x 3-carbon pyruvate molecules. (Proteins, Lipids and other Carbohydrates can also be used) (Anaerobic Stage) 2)    Link Reaction – the conversion of the 3-carbon pyruvate molecule into CO2 and a 2-carbon molecule called acetylcoenzyme A. 3)    Kreb’s Cycle – the introduction of acetylcoenzyme A into a cycle of oxidation-reduction reactions that yield some ATP and a large number of Electrons. 4)    Oxidative Phosphorylation – The Final stage of Respiration, when the majority of ATP molecules are produced.   3.     Anaerobic Respiration In plants, during Glycolysis, if there is no oxygen present then once Pyruvate is formed a Carbon is lost as Co2 and a Hydrogen and electron are used


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