Topic 19, 20, 21

• Producer


  An organism which converts light energy to chemical energy in order to produce its own nutrients
• Consumer


  An organism which gets energy from feeding on other animals or plants
• Food chain


  A diagram which shows the order of energy transfer through feeding in an ecosystem
• Food web


  A diagram showing how different food chains interact with each other
• Trophic level


  The trophic level of an organism refers to its position in the food chain, food web, pyramid of numbers or pyramid of biomass
• Pyramid of numbers


  Shows the number of organisms in each trophic level of a food chain
• Pyramid of biomass


  Shows the total mass of organisms in each trophic level of a food chain
• Biomass


  The total mass of living material
• Herbivore


  Organisms which feed on plants
• Carnivore


  Organisms which feed on animals
• Decomposer


  Organisms which break down decaying organic material
• Energy transfer in biological systems

  1. Light energy absorbed by plants

  2. Converted to chemical energy

  3. Passed to other organisms through feeding

  4. Nutrients returned to soil by decomposers
• Food chain


  • Shows the order of energy transfer between organisms
  • Starts with producers (plants)
  • Followed by consumers (herbivores and carnivores)
  • Each organism has its own trophic level
• Energy is passed between trophic levels, although this process is highly inefficient
• Reasons for energy inefficiency in food chains

  • Not all animal and plant material can be digested
  • Energy is lost through excretion and decay
  • Energy is used in other processes like movement and keeping warm
• There are usually not more than five trophic levels as too much energy would be lost to sustain another
• It is more efficient for humans to eat plants rather than animals, as there are more stages in the food chain if animals are present
• Pyramid of numbers


  Can be used to show the number of organisms in each trophic level
• Pyramid of biomass


  • Measures the total biomass of all the organisms at each trophic level
  • Tends to have a true pyramid shape as biomass is lost in each level
• A pyramid of biomass is more useful as it gives an indication of the amount of energy being passed on at each stage of the food chain
• Humans alter food webs through over-harvesting food species and introducing foreign species to habitats


  Damages food chains as other organisms do not have enough food to survive
• Carbon cycle


  Shows how carbon atoms move between the atmosphere and living organisms
• Carbon cycle


  1. Carbon dioxide in atmosphere

  2. Taken in by plants during photosynthesis

  3. Passed through food chain

  4. Returned to atmosphere during respiration and decomposition
• Carbon can be trapped in dead organisms when decomposition does not occur, forming fossil fuels
• Burning of fossil fuels and deforestation lead to increasing carbon dioxide in the atmosphere, causing global warming
• Water cycle


  1. Water evaporates from bodies of water and plants

  2. Water vapour rises and condenses to form clouds

  3. Precipitation falls as rain, snow, hail etc.

  4. Water taken up by plants and animals, or returns to bodies of water
• Nitrogen cycle


  Shows how nitrogen is converted to different forms so it can be used by living organisms
• Nitrogen cycle


  1. Nitrogen gas in air

  2. Fixed into nitrate ions by nitrogen-fixing bacteria

  3. Absorbed by plants and passed through food chain

  4. Returned to soil as ammonia or urea during decomposition
• Population


  A group of organisms of the same species living together in one habitat
• Community


  Populations of many different species living together in one ecosystem
• Ecosystem


  A system in a specific area which contains a variety of living organisms which work together within the environment
• Factors affecting rate of population growth

  • Food supply
  • Predation
  • Disease
• Over the last 250 years, the human population has risen from just over 1 billion to 7.6 billion
• Rapid human population growth leads to deforestation, increased fossil fuel use, global warming, habitat damage, and strain on services like healthcare and education, lowering quality of life