Module 6.3.1 - Ecosystems

• Ecosystem


  All living organisms and nonliving components and their interactions

  • Made up of all the living organisms that interact with one another in a defined area, and also the physical factors present in that region (can vary dramatically in size)
• Biotic factors


  The living organisms that inhabit an environment e.g. animals which compete for food, space etc.

  
• Abiotic factors

  The non-living or physical factors

  
• Abiotic factors- Light


  light is generally needed for photosynthesis

  areas with less light may need to be adapted to these conditions e.g. have greater leaf surface area
• Abiotic factors- Temperature


  controls enzyme controlling metabolic reactions

  at higher temperatures: plants develop more rapidly, ectothermic animals

  changes in temperature: can lead to migration, hibernation, trigger leaf fall/dormancy/flowering in plants
• Abiotic factors- Water availability


  needed for photosynthesis lack of water causes plants to wilt (not turgid)
• Abiotic factors- Oxygen availability


  lack of oxygen can lead to suffocation of the organism especially in aquatic organisms where the water is warm (slow flow rate)
• Abiotic factors- Edaphic soil factors (3 types)


  clay- fine particles, easily waterlogged, clumps when wet

  loam- different-sized particles, retains water, not become waterlogged

  sandy- coarse, well separated particles that allow free draining, doesn't retain water and easily eroded
• Biomass


  the total mass of organisms in a given area or volume.
• Trophic level


  Each stage in a food chain or food web
• Producer


  organism that converts light energy into chemical energy by the process of photosynthesis (essentially making their own food)

  
  

  First trophic level
• Consumers


  An organism that obtains energy and nutrients by feeding on other organisms or their remains.

  
  

  Primary consumer- animal eats producer

  Secondary consumer- animal eats primary consumer

  and so on...
• Why do food chains rarely go above the tertiary consumer stage?

  There is not sufficient biomass and stored energy left to support any more organisms
• Decomposers


  Organisms that break down the dead remains of other organisms releasing nutrients back into the ecosystem
• To calculate biomass at each trophic level...


  ...you multiply the biomass present in each organism by the total number of organisms in that trophic level
• Measuring biomass


  scientists calculate dry mass by killing organism placing in oven until all water evaporates only small sample taken (to minimise destruction)
• Units for biomass (on


  land and water)land: g m^-2

  water: g m^-3
• Ecological efficiency


  the efficiency with which energy is transferred from one trophic level to the next

  
• Why does the biomass decrease at each stage of a food chain?


  When animals eat, only a small proportion of the food they ingest is converted into new tissue. It is only this part of the biomass (energy) which is available for the next trophic level to eat
• Efficiency at producer level

  Producers convert 1-3% of sunlight they receive into chemical energy and biomass:

  
  

  -not all solar energy is used for photosynthesis (most of its reflected)

  -other factors may limit photosynthesis e.g. water availability

  -proportion of energy is 'lost' as it is used for photosynthetic reactions

  
• Net production formula

  Gross production - respiratory losses (plant respiration)

  
• Efficiency at consumer levels

  Consumers convert at most 10% of the biomass in their food to their own organic tissue:

  
  

  -not all biomass of organism is eaten

  -some energy transferred to environment as heat

  -some parts of organism are indigestible

  -some energy lost in excretory material e.g. urine or faeces
• Ecological efficiency formula

  100 x (energy or biomass available after the transfer/energy or biomass available before the transfer)

  
• How do human activities manipulate biomass

  Agriculture-manipulating the environment to favour plant species, best abiotic conditions provided, competition removed etc.

  Agriculture creates simple food chains with thefewest trophic levels(this means more energy is transferred into biomass that can be eaten by humans and so only minimum energy is lost)
• Decomposers (saprophytes- obtain energy from dead or waste organic material)


  secrete enzymes that digest molecules in organic material and convert them to inorganic forms (e.g. nutrients)
• Detrivores/Detritus


  an animal that feeds on dead organic material, especially plant detritus(dead or decaying material).

  
• Nitrogen fixation

  Process of converting nitrogen gas (N2) into ammonia using nitrogen - fixing bacteria
• Name the two types of nitrogen-fixing bacteria and enzyme involved

  Azotobacter

  and

  Rhizobium

  (both contain enzyme nitrogenase)
• How do nitrogen-fixing bacteria function

  (Azotobacter and Rhizobium)Using the enzyme nitrogenase, they combine atmospheric Nitrogen (N2) with Hydrogen (H2) to form Ammonia (NH3)

  which is then absorbed by plants

  (symbiotic relationship: plant gains AA, then produces carbohydrates used by bacteria)
• Nitrification


  Process by which ammonium compounds in the soil are converted into nitrogen - containing molecules(e.g. NO3-)

  
• Nitrification process

  Nitrifying bacteria (Nitrosomonas)oxidises

  Ammonia (NH3)into Nitrites (NO2-)

  Nitrobacteroxidise Nitrites (NO2-)into Nitrates (NO3-)

  
• Denitrification


  process by which bacteria convert nitrates into nitrogen gas

  in anaerobic conditions only, since bacteria use nitrates as a source of energy for respiration

  
• Ammonification


  decomposers convert nitrogen-containing molecules into ammonia
• Nitrogen cycle diagram

  
• Carbon Cycle Steps

  1. Carbon enters the atmosphere as carbon dioxide from respiration and combustion.

  2. Carbon dioxide is absorbed by producers to make carbohydrates in photosynthesis.

  3. Animals feed on the plant passing the carbon compounds along the food chain. Most of the carbon they consume is exhaled as carbon dioxide formed during respiration. The animals and plants eventually die.

  4. The dead organisms are eaten by decomposers and the carbon in their bodies is returned to the atmosphere as carbon dioxide. In some conditions decomposition is blocked. The plant and animal material may then be available as fossil fuel in the future for combustion.
• Fluctuations in carbon dioxide

  -co2 levels fluctuate during the day and seasonally depending on rate of photosynthesis (highest during the night)

  
  

  -co2 levels has increased due to combustion of fossil fuels and deforestation

  
  

  -causes increase in greenhouse effect and contributes to global warming

  
  

  -positive feedback at high temps causes less gas to dissolve in the sea
• Succession


  (ecology) the gradual and orderly process of change in an ecosystem brought about by the progressive replacement of one community by another until a stable climax is established
• Two types of succession

  primary succession and secondary succession
• Primary succession


  this occurs on an area of land that has been newly formed or exposed such as bare rock. there is no soil or organic material present to begin with
• Secondary succession


  this occurs on areas of land where soil is present, but it contains no plant or animal species. An example would be the bare earth that remains after a forest fire