Ecosystems 6.3.1 Flashcards
Ecosystem
The interactions between all the living organisms and the non-living conditions found in an area (biotic and abiotic factors). Dynamic system.
Examples of biotic factors
- organisms present
- size of populations
- competition between or within a species
Examples of abiotic factors
- light availability
- temperature
- water availability
- oxygen availability
Equation for efficiency of biomass transfers between trophic levels
efficiency = biomass transferred / biomass intake x100
ie. energy after transfer / energy before transfer x 100
Biomass
the mass of living material present in a particular place of in particular organisms. Can be equated to energy content
How do you measure biomass?
Calculate the dry mass of organisms present by heating to 80°C. However this presents problems as organisms have to be killed to be dried
Reasons for energy loss between trophic levels
- plants can’t use all the light energy from the sun. Some is wrong wavelength, some passes straight through the leaves, some hits non-photosynthesising parts eg. bark
- some parts of food aren’t eaten by organisms eg. roots, bones so energy isn’t taken in and is passed to decomposers
- some parts of food are indigestible so come out as faeces. also passed to decomposers
- respiratory loss (energy used for movement/heat)
Net productivity
the amount of energy stored that becomes biomass (≈ 10%). This energy is available to the next trophic level
Equation for net productivity
net productivity = gross productivity - respiratory loss
Gross productivity
energy available - energy not taken in
ie. all the energy that an organism takes in. Not all of this is available to the next trophic level, due to respiratory losses
How do human activities manipulate the transfer of biomass through ecosystems?
- plants and animals are provided with the abiotic conditions they need to survive for agricultural purposes
- competition is removed
- threat of predators is removed
- use of herbicides/ insecticides
- minimise the no. trophic levels in the food chain to minimise loss of energy/biomass
Decomposer
- organism that feeds on/breaks down dead plant or animal matter, converting organic compounds into inorganic nutrients available to photosynthetic producers.
- Mostly microorganisms.
- saprotrophic
Detritivores
Speed up the decay process by feeding on detritus (dead and decaying material). Break it into smaller pieces of organic material, increasing the SA for decomposers to work on.
eg. woodlice and earthworms
Nitrogen fixation
- combines atmospheric nitrogen with hydrogen to make ammonia which can be used by plants
- N₂ + 3H₂ → 2NH₃
- by nitrogen-fixing bacteria
- -contain enzyme nitrogenase
- -eg. Azotobacter, Rhizobium
Azotobacter
Nitrogen-fixing bacteria
Free living soil bacteria
Rhizobium
Nitrogen-fixing bacteria
Lives inside root nodules
Have a symbiotic mutualistic relationship with the plant
- plant gains a.as from Rhizobium
- bacteria gains carbs from made plant during photo.
Nitrification
- ammonium compounds in soil are converted to nitrogen-containing molecules that can be used by plants (nitrites and nitrates)
- by nitrifying bacteria
- nitrification is an oxidation reactions so only occurs in well aerated soil
- Nitrosomonas oxidises NH₃ to nitrites NO₂⁻
- Nitrobacter oxidises nitrites NO₂⁻ to nitrates NO₃⁻
Nitrosomonas
oxidises NH₃ to nitrites NO₂⁻
Nitrobacter
oxidises nitrites NO₂⁻ to nitrates NO₃⁻
Denitrification
In the absence of O₂ eg. waterlogged soils
Denitrifying bacteria convert nitrates NO₃⁻ back to atmospheric N₂
The bacteria use the nitrates as a source of energy for resp.
Ammonification
decomposers convert N₂ containing molecules in dead organisms, faeces, and urine into NH₃ compounds
What are the names of the processes involved in the carbon cycle?
decomposition, photosynthesis, respiration, combustion, weathering
Why is it important to recycle carbon?
Present in all organic molecules eg. fats, carbs, proteins
succession
the process by which an ecosystem changes over time,
as a result of changes to the environment, causing the plant and animal species present to change
primary succession
area of land that is newly formed or exposed. No soil or organic material present initially
eg. bare rock
secondary succession
areas of land where soil is present , but there are no plant or animal species
eg. bare earth after a forest fire
examples of situations where primary succession takes place
- volcano erupts and creates a layer of new rock
- sand is blown by the wind or deposited by the sea to create new sand dunes
- silt and mud deposited at river estuaries
- glaciers retreat, depositing rubble and exposing rock
what are the stages in succession known as
seral stages
name the stages of primary succession
pioneer species
intermediate community
climax community
what are the adaptations of pioneer species that make them suitable to colonise inhospitable environments?
- can produce large quantities of seeds or spores which are blown by the wind and deposited onto new land
- seeds germinate rapidly
- can photosynthesise
- can tolerate extreme environments
- can fix nitrogen from the atmosphere (adding to the mineral content of soil)
humus
organic component of soil that is formed when organisms from the pioneer species die and decompose
contains minerals eg. nitrates and can retain some water
allows secondary colonisers to be supported
what are the 2 components of the new soil formed in the intermediate community?
weathering of bare rock
humus
what is the climax community
last seral stage of succession
community is in a stable state
a few dominant species
when is the highest biodiversity during succession?
mid-succession, not at the climax community
as later on dominant species outcompete pioneer and intermediate species
climatic climax
the climax community for a particular climate
plagioclimax
human activity causes deflected succession
the final stage (climax community) is known as a plagioclimax
how is succession deflected?
- grazing animals trample vegetation
- removal of vegetation to plant crop
- burning to clear forest
how to measure the distribution of organisms
- belt or line transect (systematic sampling)
systematic sampling
different areas within a habitat are identified and then sampled separately
allows scientists to see how abiotic factors affect the distribution of organisms
how to measure the abundance of a plant species
quadrats placed randomly
how to measure the abundance of an animal species
capture-mark-release-recapture
estimated pop. size = no. in 1st sample x no. in 2nd sample / no. recaptured marked individuals
