Ecosystems

Cards (48)

  • Ecosystem - All the living organisms that interact with one another in a defined area and all the physical factors present in that area
  • Biotic factors:
    • interactions between living organisms
    • e.g. competition over food, space, breeding partners
  • Abiotic factors:
    • non-living/physical factors within an ecosystem
    • Light
    • Temperature
    • Water Availability
    • Oxygen Availability
    • Edaphic (soil) factors
  • Light:
    • plants are directly affected by light levels
    • in low light, certain plants have adapted to cope e.g. larger leaves, photosynthetic pigments that require less light
  • Temperature:
    • effects enzyme controlled reactions
    • can cause migration and hibernation in animals, and leaf-drop, dormancy and flowering in plants
  • Water Availability:
    • lack of water can lead to stress
    • stress can lead to death
  • Oxygen Availability:
    • Aquatic Environments:
    • fast flowing cold water has high concentrations of oxygen
    • Water logged soil:
    • air spaces in the soil are not full of water therefore less oxygen available for the plantsn
  • Edaphic factors:
    • different soils have different particle sizes. this affects what lives in them:
    • clay - fine particles, easily waterlogged, forms clumps when wet
    • loam - different-sized particles, retains water but does not become water logged
    • sandy - coarse, well-separated particles that allow free draining, does not retain water and is easily eroded
  • the sun is the source of energy for nearly all ecosystems on earth due to photosynthesis
  • Trophic level - each stage in a food chain
  • producer - first trophic level (organism converts sunlight into energy by photosynthesis)
  • consumers - found in the subsequent trophic levels after producers, they feed on other organisms
  • decomposers - break down dead organisms releasing nutrients back into the ecosystem
  • Biomass:
    • the mass of living material present in a particular place or in a particular organism
    • it can be equated to the energy content of a trophic level
    • can be represented by a pyramid of biomass
    • biomass is calculated by working out the dry mass of the organism (organism is killed and placed in an 80 degree oven to remove all water)
    • measured in grams per square meter for areas of land and grams per cubic metre for areas of water
  • as trophic level increases, biomass and energy content decrease (mostly)
  • ecological efficiency - the efficiency with which biomass or energy is transferred from one trophic level to the next
  • producers only convert 1-3% of the sunlight they receive into chemical energy because:
    • 90% of solar energy is reflected, some is transmitted through the leaf, some is an unusable wavelength
    • photosynthesis limited by other factors
    • some energy is used to drive photosynthetic reactions
  • Gross production - the total solar energy that plants convert to organic matter. 20-50% of this is used in respiration, the rest is converted to biomass
  • net production = gross production - respiratory losses
  • primary production - net production in a producer
  • secondary production - net production in a consumer
  • consumers at each trophic level convert 10% at most of the biomass in their food to their own organic tissue because:
    • not all biomass is eaten (bones)
    • some energy is transferred as metabolic heat
    • some parts of the organism aren't digested
    • some is lost in excretory products e.g. urine
  • only 0.001% of the total energy present in the incident sunlight will become biomass in the tertiary consumer
  • ecological efficiency = energy or biomass available after the transfer/ energy or biomass available before the transfer x100
  • farming involves manipulating environments so that plants and animals can thrive and high yields can be achieved:
    • competition is removed e.g. kill weeds
    • protect organisms from predators e.g. fences
    • watering plants
    • provide warmth e.g. sheds/stables
  • Farming creates short food chains which reduces energy loss:
    • producing crops for humans only involves two trophic levels
  • decomposition - a chemical process where a compound in broken down into smaller molecules or its constituent elements
  • decomposer - organism that feeds on and breaks down dead organic matter. they turn organic compounds into inorganic compounds that are then available to photosynthetic organisms
  • Saprobiotic nutrition - an organism that obtains their energy from dead or waste organic matter
  • saprotrophic nutrition - food is digested externally by the secretion of enzymes
  • detritivores - speed up the decaying process by feeding on dead and decaying matter. this process breaks down the material into smaller pieces, increasing the SA for decomposers
  • Nitrogen - essential for making amino acids; 78% of the air is nitrogen
  • nitrogen fixation:
    • performed by nitrogen fixing bacteria e.g. Azotobacter (free-living) and Rhizobium (root nodules, symbiotic with plant)
    • the enzyme nitrogenase combines atmospheric nitrogen with hydrogen to produce ammonia
  • Nitrification:
    • performed by nitrifying bacteria
    • ammonium compounds are converted into nitrites then nitrates
    • oxidation reaction; only occurs in well-aerated soils
    Nitrosomonas + ammonium --> nitrites
    Nitrobacter + nitrites --> nitrates
  • Denitrification:
    • lack of oxygen
    • Denitrifying bacteria (pseudomonas aeruginosa) convert nitrates in the soil back into nitrogen gas
    • the bacteria use the nitrates as a source of energy for respiration causing nitrogen gas to be released
  • Ammonification:
    • decomposers convert nitrogen-containing molecules in dead organisms, faeces and urine into ammonium compounds
  • Carbon:
    • 0.04% of the atmosphere is carbon
    • levels of CO2 fluctuate between day and night and seasons due to the availability of light and leaf loss
    • CO2 levels have increased significantly due to increased burning of fossil fuels
    • deforestation results in fewer trees to perform photosynthesis and take in CO2
    • the increase in sea temperatures means that less CO2 is dissolved in the sea water thus more CO2 is released in a positive feedback loop
  • Succesion - the progressive replacement of one dominant type of species or community by another in an ecosytem until a stable climax community is reached
  • primary succession - occurs in an area that is newly formed or exposed such as bare rock. there is no soil/organic matter to begin with:
    • volcanoes erupt, depositing lava which cools into igneous rock
    • sand is blown by wind or deposited in the sea to create dunes/banks
    • silt and mud are deposited at river estuaries
    • glaciers retreat depositing rubble and exposing rock