6.3.1 - Ecosystems Flashcards
What is an ecosystem?
a defined area made up of living organisms that interact with eachother and factors present
- range in size
- are dynamic
eg. rockpool, field, tree
What are abiotic factors?
non-living factors
What are biotic factors?
living factors (interactions between organisms)
What biotic factors affect ecosystems?
competition
- food
- territory
- mates
What abiotic factors affect ecosystems?
- light
- temperature
- water availability
- oxygen availability
- edaphic (soil) factors
How does light affect ecosystems?
-needed for photosynthesis
How does temperature affect ecosystems?
- affects enzymes and ∴ metabolic reactions
- plants and ecothermic animals develop quicker in warmer temps
- temp changes trigger migration and hibernation
How does water availability affect ecosystems?
- lack of water leads to water stress
- lack of water causes plants to wilt (water is needed to keep cells turgid and plant upright) except xerophytes
- needed for photosynthesis
How does oxygen availability affect ecosystems?
- in aquatic ecosystems fast-flowing cold water is beneficial as it contains a high O2 conc
- in water logged soil, air spaces are filled with water instead of oxygen
- needed for aerobic respiration
How do edaphic (soil) factors affect ecosystems?
different soil types have different particle sizes (which effects which organisms can survive there)
- clay - fine particles, easily waterlogged, clumps when wet
- loam - diff particle sizes, retains water, not easily waterlogged
- sandy - coarse/well separated particles, free draining, water not retained, easily eroded
What is biomass?
the mass of living material present in an organism
How is biomass transfer represented?
in food chains, food webs and pyramids of biomass
biomass at trophic level =
biomass in each organism x total no. organisms in trophic level
Why are producers not 100% efficient?
not all sunlight is converted into biomass
- some light energy is reflected or transmitted through the leaf so isn’t all used for photosynthesis
- other factors limit photosynthesis
Why isn’t all the biomass transferred between trophic levels?
- not all biomass is eaten (eg, bones, roots, etc)
- energy is lost to surroundings (as metabolic heat from movement and respiration)
- some parts of food eaten are indigestible so are egested as faeces
- some energy is lost as excretory materials (eg. urine)
ecological efficiency =
biomass transferred
_________________________ x 100
biomass before transfer (intake)
What is ecological efficiency?
efficiency which biomass is transferred from one trophic level to the next
How do human activities manipulate the transfer of biomass through ecosystems?
agriculture (environment is manipulated to favour crops being grown and animals being reared)
- plants and animals are provided with abiotic conditions they need (eg. water, warmth)
- competition from other species is removed (eg. using pesticides, fences to prevent predators)
- agriculture shortens food chains (only 2/3 trophic levels) so less energy is lost
What is decomposition?
chemical process where a compound is broken down into smaller molecules so that they are more usable and can be returned to the environment
What is a decomposer?
an organism that feeds on and breaks down dead plant/animal matter
- are saprotrophs (obtain energy from dead/waste materials)
- digest food externally by secreting enzymes so that they can then absorb it
eg. fungi, bacteria
What is a detritivore?
an organism that speeds up decay by feeding on detritus (dead, decaying matter) which breaks it into smaller pieces
- digest internally
- increases SA for decomposers to work on
eg. woodlice, earthworms
What is the difference between decomposers and detritivores?
- decomposers digest the dead matter externally (using enzymes) and then absorb it but detritivores digest it internally
- decomposers are fungi and bacteria but detritivores are animals
- detritivores break down the organic material into smaller pieces of organic material (increasing SA for decomposers) whereas decomposers break the organic material into inorganic material.
What is nitrogen fixation?
process where atmospheric nitrogen gas is combined with hydrogen to produce ammonia
N2 + H2 → NH3
-nitrogenase enzyme involved
How is nitrogen fixed by living organisms?
- by nitrogen fixing bacteria in root nodules
eg. Rhizobium - by nitrogen fixing bacteria in soil
eg. Azotobacter
How is nitrogen fixed by non-living processes?
- by Haber process
- by lightning
What is nitrification?
process where ammonium compounds are converted into nitrites and nitrates
NH3 → NO2 - → NO3 -
-oxidation rxn (only occurs in well-aerated soil)
-uses nitrifying bacteria
two steps:
1) nitrifying bacteria (eg. Nitrosomonas) oxidise ammonium compounds into nitrites
2) nitrifying bacteria (eg. Nitrobacter) oxidise nitrites into nitrates
What are the two steps of nitrification?
1) nitrifying bacteria (eg. Nitrosomonas) oxidise ammonium compounds into nitrites
2) nitrifying bacteria (eg. Nitrobacter) oxidise nitrites into nitrates
What is denitrification?
process where nitrates in soil are converted into nitrogen gas in the absence of oxygen
- only occurs in anaerobic conditions
- denitrifying bacteria involved (use nitrates as energy source for respiration)
What is ammonification?
process where nitrogen compounds in waste and dead organisms are converted into ammonium compounds
-by decomposers (eg. fungi, bacteria)
Why is nitrogen important for living organisms?
is needed to make proteins and nucleic acids
What stages occur in the nitrogen cycle?
- nitrogen fixation (of nitrogen gas into ammonia)
- nitrification (of ammonium compounds into nitrites and nitrates)
- uptake and assimilation (of nitrates into plants)
- transfer of nitrogen in food chain (from plants to animals)
- death of plants/animals + ammonification (converted into ammonium compounds by decomposers)
- denitrification (nitrates converted back into nitrogen gas)
What stage of the nitrogen cycle is Nitrosomonas involved in?
nitrification
What stage of the nitrogen cycle is Nitrobacter involved in?
nitrification
What stage of the nitrogen cycle is Azotobacter involved in?
nitrogen fixation
free living in soil
What stage of the nitrogen cycle is Rhizobium involved in?
nitrogen fixation
living in root nodules
How do carbon dioxide levels increase in the atmosphere?
- combustion of fossil fuels (releases CO2 that had been trapped in the Earth)
- deforestation (less photosynthesis ∴ less CO2 taken in from atmosphere)
- global warming (reduces carbon bank in oceans -higher temp = less gas dissolved in seas ∴ more CO2 released into atmosphere)
What stages occur in the carbon cycle?
- decomposition (releases CO2 into atmosphere)
- photosynthesis (CO2 is used by plants)
- plants are eaten by animals (carbon-containing compounds are eaten and made)
- respiration (releases CO2 into atmosphere)
- death and decay of plants and animals
- combustion of fossil fuels (releases CO2 into atmosphere)
What is succession?
the transition of an ecosystem over time
What is a seral stage?
a step in succession
What is primary succession?
the development of an ecosystem when plants grow where nothing has before (eg. on rock)
What is secondary succession?
the development of an ecosystem when plants grow where soil is present but no species currently are
-ecosystem has previously been destroyed
What are the stages of primary succession?
- barren land (inhospitable environment)
- pioneer community (land colonised by pioneer species)
- intermediate community (secondary colonisers, tertiary colonisers + shrublands)
- climax community reached (stable state)
How do pioneer species colonise barren land (in primary succession)?
- arrive as seeds/spores
- produce a lot of seeds/spores
- germinate rapidly
- photosynthesise and fix nitrogen
- are very tolerant to extreme living conditions
Name an example of an organism in a pioneer community
lichen
How does a pioneer community change to an intermediate community?
- rock is weathered, producing particles that are a basis of soil
- death/decomposition of pioneer species creates humus
- this then supports new plant species that arrive as seeds/spores (secondary colonisers)
- other plant species arrive (tertiary colonisers)
- as rock is eroded more and more and soil becomes deeper and richer in nutrients, larger plants can grow
Name an example of secondary colonisers
mosses
Name two examples of tertiary colonisers
ferns
grasses
How is a climax community reached (in primary succession)?
-community reaches a stable state where there is very little change and a few dominant plant species present
Name an example of a climax community
woodland
What happens in secondary succession?
- land (in an intermediate or climax community) is altered (eg. by fire, disease, agriculture)
- land is recolonised
- succession occurs until a climax community is reached
What is deflected succession?
succession where a climax community is stopped artificially, forming a plagioclimax
eg. for agriculture or conservation
What is a plagioclimax?
the final stage of deflected succession
eg. farm field
Why is animal succession slower than plant succession?
animals must move in from neighbouring areas
What is distribution?
where organisms are located in an ecosystem
How is the distribution of an organism within an ecosystem measured?
quadrats placed along a line/belt transect
What is abundance?
the number of individuals of a species present in an area in a given time
How is the abundance of plants in an ecosystem measured?
using quadrats
estimated population of plants =
no. individuals
____________
area of sample
How is the abundance of animals in an ecosystem measured?
using capture-mark-release-capture
- capture and mark as many organisms as possible
- release
- allow time to distribute
- recapture as many organisms as possible
- record marked and unmarked organisms
- use Lincoln index to find estimated population
estimated population of animals =
Lincoln’s index
no. individuals in 1st sample x no. individuals in 2nd sample
____________________________
no. recaptured marked individuals
