1.6

• Sunlight


  Source of all energy in biological systems
• Photosynthesis


  1. Sunlight absorbed by photosynthetic organisms (producers)

  2. Converted to chemical energy (biomass)
• Biomass


  • Transferred between organisms during feeding, used for growth, repair, etc.
  • Eventually returns to soil when decomposers break down dead material and waste
• Food chain


  Describes the feeding relationships between organisms and the resultant stages of energy and biomass transfer
• Trophic levels


  • Producer
  • Primary consumer
  • Secondary consumer
  • Tertiary consumer
• Producers


  • Provide all energy for the food chain via photosynthesis
  • The rest of the food chain involves the transfer of this energy
• Primary consumers


  Normally herbivores
• Decomposers


  Can obtain energy from dead organisms at any point in a food chain
• Food web


  Shows how different food chains are interlinked and how members of an ecosystem are interdependent
• Energy transfer is inefficient
• Reasons for energy loss in a food chain

  • 90% of the sun's energy is reflected
  • Respiration to generate heat energy, energy for movement etc. in animals
  • Some parts of organisms are indigestible
  • Egestion, excretion
• There are rarely more than four or five trophic levels in a food chain; above this, there is insufficient energy to support another breeding population
• Pyramid of numbers


  Represents the number of organisms per unit area at each trophic level
• Pyramid of biomass


  Shows the dry mass of living material per unit area at each trophic level
• Pyramids of biomass generally take a 'true pyramid' form (as energy is lost at each trophic level)
• Pyramids of numbers are often not pyramid shaped as they don't take size and mass of organisms into account
• Decomposition


  Breakdown of dead materials into simpler organic matter
• Decomposers


  • Important in the recycling of organic matter, returning vital nutrients to the soil
  • Release enzymes which catalyse the breakdown of dead material into smaller molecules such as nitrates, phosphates etc.
  • Ensure a balance in ecosystems: the processes that remove materials from the soil are balanced by the processes that return them
• Nutrient cycles


  • Processes by which materials cycle through the living and non-living components of an ecosystem
  • Fixed amount of nutrients on Earth which must be constantly recycled
• Carbon cycle


  1. Photosynthesising plants remove CO2 from the atmosphere

  2. Eating passes carbon compounds along a food chain

  3. Respiration in plants and animals returns CO2 to the atmosphere

  4. Organisms die and decompose, decomposers break down dead material and release CO2 via respiration

  5. Combustion of materials (e.g. wood, fossil fuels) releases CO2
• Nitrogen cycle


  1. Organisms die and decompose, decomposers break down proteins and urea into ammonia

  2. Bacteria in the soil convert ammonia into nitrates which are taken up by plants and used to build proteins

  3. Nitrogen-fixing bacteria convert nitrogen gas into nitrates which are taken up by plants

  4. Feeding passes nitrogen through the food chain

  5. Denitrifying bacteria convert nitrates in the soil back to nitrogen gas
• The needs of the human population sometimes conflict with the conservation of the environment
• It is important to balance the need for resources with the need to preserve the biodiversity of ecosystems
• Intensive farming


  Agricultural system characterised by the use of machinery, chemicals (fertilisers, pesticides etc.) and battery methods to maximise space and produce high crop yields
• Advantages of intensive farming

  • Maximum crop yields - cheaper to produce and greater profits
  • Maximises space for crops and machinery
  • Enables more food to be grown to meet the demands of the growing population
• Disadvantages of intensive farming

  • Reduces biodiversity
  • Excess fertiliser can wash into water sources causing eutrophication and death of many species
  • Chemicals may enter the human food chain or cause damage to other wildlife
  • Hedgerows (food source and shelter to many species) removed
  • Battery farming may be seen as unethical
  • Use of antibiotics to minimise risk of disease leads to antibiotic resistance
  • High input cost
• Eutrophication


  1. Excess fertiliser or untreated sewage enters rivers and lakes

  2. Nutrient build-up in water

  3. Algal bloom blocks sunlight

  4. Aquatic plants cannot photosynthesise, less oxygen produced

  5. They die and decompose

  6. Decomposers further deplete oxygen levels

  7. Animals can no longer respire aerobically so die
• Some chemicals that do not break down rapidly (e.g. heavy metals) can enter food chains and accumulate in organisms
• At higher trophic levels, pollutants become very concentrated and may become toxic to larger animals such as whales
• Electronic meters


  Used to detect water pollution by measuring changes in pH or oxygen levels
• Indicator species


  Species whose presence or absence in an environment provides indication of environmental conditions e.g. pollution levels
• Indicator species are less accurate than non-living indicators and do not provide a definitive figure for pollution levels