Ecosystems Flashcards
what is an ecosystem
all the interacting living organisms and non-living factors within an area
what is a key characteristic of an ecosystem
it is dynamic
what is a habitat
place where an organism lives
what is biomass
the mass of living material
why is not all the energy transferred through trophic levels
- plants don’t use all the light energy that reaches their leaves
- some light is the wrong wavelength so is reflected or passes straight through the leaves
- some light energy can’t be used as it hits parts of the plant that aren’t photosynthetic
- not all parts are eaten/digested (plants contain lots of undigestible parts eg. cellulose cell walls)
what is the net productivity
the amount of energy that is available to the next trophic level
how can percentage efficiency of energy transfer be calculated
net productivity of trophic level / net productivity of previous trophic level
x100
how can you calculate how efficient organisms in one trophic level are at converting what they eat into energy for the next trophic level
energy transferred/energy intake x 100
Farmers try to reduce the amount of energy lost from the food chain in order to increase productivity, what do these methods include and why are they done?
(6 methods)
- herbicides, kill weeds that compete reducing competition
- fungicides, kill fungal infections that damage crops so more energy used for growing than fighting infection
- insecticides, kill insects that eat crops, less biomass lost
- introduce natural predators, these eat the pests so less biomass lost
- fertilisers, chemicals provide crop with minerals
- rearing livestock intensively, controls conditions so more energy used for growth
how might a farmer rear animals intensively
animals kept in thermostatically controlled room - less energy used maintaining body temp
given feed that is higher in energy
kept in small cages to reduce energy lost through movement
(these have ethical concerns)
how is carbon returned to the atmosphere ( 6 ways)
- respiration
- combustion, burning of fossil fuels
- release from volcanoes, limestone and chalk drawn into earths crust undergo chemical changes that release CO2
- weathering, rocks are broken down by chemicals in rainwater (Acid rain) this causes mineral ions and bicarbonate ions to be released from the rock into grounwater
- release from and absorbtion into ocean - CO2 dissolves directly into oceans, transported by currents and later released.
why can plants not obtain nitrogen from the atmosphere
N2 is unreactive and is a stable compound as contains a triple bond
what are the 2 types of bacteria that convert nitrogen gas to ammonia during nitrogen fixation, where are these 2 types found
Rhizobium - found inside root nodules of legumious plants (mutualistic relationship)
Azotobacter- found free living in the soil
outline the process of ammonification
Nitrogen compounds from dead plants and animals are broken down by decomposers into ammonia which is returned to the soil.
outline the process of nitrification, what are the 2 types of bacteria involved
ammonium ions (NH3) converted into nitrites (NO2 - ) by Nitrosomonas
nitrates are converted to nitrates by nitrobacter (NO3-)
nitrates are taken up by plants via assimilation
outline the process of dentrification
nitrates (NO3-) are converted back into nitrogen gas via dentrifying bacteria that use nitrates to carry out respiration.
happens under ANAEROBIC CONDITIONS eg. waterlogged soil
apart from bacteria, what 2 other ways nitrogen fixation can occur
naturally - lightning fixed atmospheric nitrogen
artificially - Haber process
how much nitrogen and oxygen is there in the atmosphere
nitrogen - 78%
oxygen - 20%
what is succession
process by which an ecosystem changes over time, occures in stages, at each stage a new species changes the environment so it is less suitable for the previous species therefore each existing species is outcompeted by the new species
when does primary succession occur
occurs on land that has been newly formed or exposed resulting in no soil or organic material to start with
outline the pioneer stage of succession
- seeds and spored are blown in by the wind and begin to grow.
- first species to colonise are called the pioneer species.
- Abiotic conditions are hostile + recquire specialised species eg Marram grass
these species die and decompose to form a basic soil making conditions less hostile.
New organisms come in, which die and decompose adding more organic material to soil.
Nitrogen fixing bacteria makes ammonia which is used by plants
larger plants grow and retain water and nutrients
outline the later stages of succession
plants and animals that are better adapted move in and create competition to become the dominant species. This changes the abiotic environment.
ecosystem becomes complex resulting in a climax community
what is a climax community
the ecosystem is supporting the largest and most complex community of organisms - steady state.
what is secondary succession
occurs on land that has been cleared of all plants but soil remains. This succession occurs at a later stage, the pioneer species are larger plants.
usually occurs as a result of natural disaster or drastic change to environment.
what is prevention and what is the name of the climax communtiy that occurs as a result of it
human activity prevents succession preventing the normal climax community developing.
plagioclimax
what is deflected succession
when succession is prevented by human activity, but the plagioclimax is different to any of the natural stages of the ecosystem.
eg - regularly mown grassy field wont develop woody plants even if climate could support
what is meant by the term population
group of organisms of the same species living in the same area
what is meant by the term community
all the populations of different species in the same area at the same time
what is a niche
an organisms role within the ecosystem eg. position in food web
what is gross primary production
the total energy entering a food chain as a result of photosynthesis
what is net primary production
what energy is left over to. create new biomass in the plant, and so is the amount of biomass that can be passed on to next level
what are the units for production
KJ H -1 year -1
what are the biomass units for land mammals
g m -2
what are the biomass units for marine animals
g m -3
