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 organictissue 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 digestedexternally 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 barerock. there is no soil/organic matter to begin with:
volcanoeserupt, 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