Organisation of an Ecosystem

• Population


  A species that occupy the same habitat
• Habitat


  The place in which an organism lives
• Community


  Populations of different species interacting
• Ecosystem


  The interactions between the biotic and abiotic factors in an area
• Food chains


  • Show the feeding relationships of different organisms and the flow of energy between the organisms

  
• Biomass


  The total mass of living material
• Trophic levels


  The stages in a food chain

  
• Arrows in a food chain

  Represent the direction of biomass transfer

  
• Simple food chain


  • producer → primary consumer → secondary consumer → tertiary consumer
• Producer


  An organism that makes its own food
• Primary producers


  • Photosynthetic organisms like green plants and algae that trap energy from the sun
• Primary consumer


  An organism that feeds on producers
• Secondary consumer


  An organism that feeds on primary consumers
• Tertiary consumer


  An organism that feeds on secondary consumers
• Predator


  A consumer that kills and eats other animals
• Prey


  An animal that is killed and eaten by another animal
• In a stable community


  The numbers of predators and prey rise and fall in cycles
• Producers are the first trophic level because they provide all biomass for the food chain through photosynthesis, and the rest of the food chain involves the transfer of this biomass

  
• Quadrat


  Piece of apparatus used to measure the abundance and distribution of organisms in an area
• Belt transect


  Piece of apparatus used to study the distribution of organisms across a gradient
• Mean


  The average number of organisms
• Calculating arithmetic mean


  Sum of each number of each organism/the total number of each type of organism
• Mode


  The most populous organism
• Median


  The organism that represents the middle value when the numbers of each organism are arranged from lowest to highest
• How materials cycle through an ecosystem

  Organisms take in elements from their surroundings, convert them to complex molecules which become biomass, transfer elements along food chains, and return elements to the environment during excretion and decomposition
• Molecules cycled through ecosystems

  • Oxygen
  • Carbon dioxide
  • Water
• The carbon cycle


  Plants fix carbon dioxide into organic molecules during photosynthesis, the organic carbon-containing molecules are passed onto organisms that eat the plants, carbon dioxide is released back into the atmosphere by respiration from animals and plants, and burning fossil fuels also releases carbon dioxide into the atmosphere
• Importance of the carbon cycle

  Carbon-containing molecules such as glucose are important for living organisms to grow and provide energy for vital functions within cells
• The water cycle


  Water from lakes and oceans evaporates, the evaporated water condenses into clouds and returns to earth as precipitation, the water from precipitation is useful for life on land, and the water then returns to rivers and oceans through surface runoff
• Importance of the water cycle

  Living organisms require water and the water cycle provides organisms on land with a continuous supply of water
• Microorganisms (bacteria and fungi) are important for the cycling of materials through an ecosystem because they return carbon to the environment by releasing carbon dioxide through respiration while they decompose dead matter, and the decomposition of dead matter in soil returns mineral ions to the environment for other organisms to use
• Decomposition


  The breakdown of dead materials into simpler organic matter
• How decomposers break down dead matter

  Decomposers release enzymes which catalyse the breakdown of dead material into smaller molecules
• Types of decomposition


  • Aerobic
  • Anaerobic
• Decomposition


  Breakdown of dead materials into simpler organic matter
• Decomposers


  Organisms that break down dead material into smaller molecules
• Types of decomposition


  • Aerobic decomposition (with oxygen)
  • Anaerobic decomposition (without oxygen)
• Factors affecting rate of decomposition

  • Oxygen availability
  • Temperature
  • Water content
• Why oxygen is required for decomposition


  Most decomposers require oxygen for aerobic respiration
• Oxygen availability


  As oxygen levels increase, the rate of decomposition increases. As oxygen levels decrease, the rate of decomposition decreases.