6.3.1 Ecosystems Flashcards
What is an ecosystem?
-all the living organisms living in a certain area and all the non-living physical factors(abiotic) that are present in that area—} includes biotic and abiotic factors
What are biotic factors and give examples
-biotic factors are the living features of an ecosystem and the interaction between organisms i.e food, space, territory, presence of predators, breeding partners
What is abiotic factors and give examples
-non living features of an ecosystem, such as:
-light(affects photosynthesis), -temp(affects enzyme controlled metabolic reactions—} changes can trigger migration/ hibernation & leaf-fall, dormancy, and flowering)
-rainfall/humidity(lack of water= water stress—} causes plants to wilt)
-soil nutrient availability
-wind speed= increases rate of water loss by evaporation + cooling rate
Abiotic factors- physiographic
-altitude/oxygen conc= affects animals that respire aerobically
-topography(shape of land)
-aspect(north or south facing)
-water supply
-salinity
Abiotic factors- Edophic(soil features)
-pH of water or soil(affected by enzyme activity + ion uptake)
-availability of inorganic ions(affects growth)
What is decomposition?
-chemical process in which a compound is broken down into smaller molecules–} normally because the compound cannot be directly used in its organic form
What is a decomposer?
-organism that feeds on + breaks down dead plant or animal matter–} turns organic compounds inorganic/into nutrients that are available to producers in ecosystems
Why are decomposers known as saprotrophs?
-because they obtain their energy from dead/waste organic material(saprobiotic nutrition)
-digest food externally by secreting enzymes onto dead organisms/organic waste matter–} enzymes break down complex organic molecules into simpler soluble molecules + the decomposers can absorb those molecules
What are detritivores?
-a class of organisms that help speed up decaying process by feeding on dead/decaying material-
-} break it down into smaller pieces of organic material which increases the SA for decomposition
What is the carbon cycle?
-how carbon moves through living organisms + the non-living environment—} needed to make essential compounds i.e plants use it in photosynthesis to make glucose
Carbon cycle: photosynthesis
-CO2 is absorbed by plants when they carry out photosynthesis–} converted into small carbon-containing molecules i.e glucose in plants + photosynthetic organisms
-carbon is also used in production of macromolecules i.e carbs, proteins in producers
(atmospheric CO2 and CO2 dissolved in oceans provides major source of inorganic carbon in plants)
Carbon cycle: Respiration
-carbon is returned to the air + water as all living organisms carry out respiration which produces CO2
Carbon cycle: consumption of organic molecules containing carbon
-carbon is passed onto primary consumers when they eat plants(then passed to secondary and tertiary consumers via the food chain)
Carbon cycle: decomposition
-all living organisms die + their carbon compounds re released via decomposers–} released into the atmosphere as CO2 when decomposers respire
Carbon cycle: combustion
-if dead organic matter accumulates in areas with no decomposers i.e ocean bed or bogs then the carbon can become ‘trapped’ and form fossil fuels over millions of years
-carbon is released when it is burned
Carbon cycle: release from volcanoes
-rock can be formed from dead organic matter deposited on the sea floor
-carbon can be returned to the atmosphere from these rocks via movement of tectonic plates–} undergo chemical changes + release CO2(returned to atmosphere by volcanoes)
Carbon cycle: weathering
-rocks can be eventually become land which is then weathered(broken down by exposure to the atmosphere)
-can happen chemically by rainwater(slightly acidic due to the CO2 dissolved in it) and physically i.e by plant roots, animals etc
-causes CO2 to be released back into the atmosphere
Carbon cycle: Release from + absorption into the oceans
-CO2 can also dissolve directly into the oceans from the atmosphere + be transported in the oceans by underwater currents
-CO2 can eventually return to surface and be released back into the atmosphere
How does energy enter an ecosystem?
-via photosynthesis, as plants convert energy from the sun into a form that can be used by other organisms i.e biomass
What is biomass?
-the mass of living material present in a particular place or in a particular organism
What are trophic levels and how can they be used to show energy transfer?
-trophic level= each stage in a food chain/web(diagrams that show the transfer of biomass + therefore energy through the organisms in an ecosystem)
-level 1= producer: converts light energy into chemical energy via photosynthesis
-subsequent levels= consumers: organisms that obtain their energy by feeding on other organisms
(food chains rarely go past quaternary as there is not sufficient biomass + stored energy left to support any further organism)
What is the role of decomposers in food webs?
-break down dead organisms, releasing nutrients back into the ecosystem–} recycle energy trapped in things that can’t be eaten i.e bones
How is biomass calculated?
-multiply the biomass present in each organism by the total no. of organisms in that trophic level
How is biomass represented?
-in a pyramid of biomass that shows the total dry mass (gm-2) of all organisms at each trophic level at a given time (doesn’t take into account seasonal changes)
-organisms gain biomass through the assimilation of digested compounds into organic molecules for storage + growth
Why must dry mass be recorded to calculate biomass?
-when using fresh material, water content must be discounted + the amount of water differs per organism so the technique is quite unreliable
How do scientists calculate the dry mass/biomass of organisms?
-record the mass of the sample originally
-sample must be killed and placed in an oven at 80°C until all water has evaporated(indicated by at least 2 identical mass readings)
-record mass a second time
-place back into oven for a further period of time and record mass again
-keep repeating the process until 2 consecutive weighing’s give the same reading
-multiply results from sample to get estimate of energy in 1 trophic level
-difference in energy between trophic levels is the amount of energy transferred
What are problems with measuring dry mass?
-consumer may have taken in energy from sources other than producer measured–} not accurate measure of energy transferred only between those 2 organisms
Measurements of biomass
-kgm-²(biomass of terrestrial/on land organism)
-gm-³ and kgm-³ (biomass of aquatic organisms)
-kjm-³ year-1 (used to measure energy)
pyramid of numbers
-numbers: shows the total no. of individual organisms at each level in the food chain of an ecosystem–} area of each bar represents the no. of species at that trophic level
-may be less representative than pyramid of biomass
pyramid of energy
shows the amount of biomass/energy is transferred from one trophic level to the next
-each bar represents the energy at that trophic level
-calorimeter: temp rise can be used to calculate the total energy measured from the burning biomass
Efficiency of biomass + energy transfer
-biomass is nearly always less than the trophic level below because not all the energy(i.e sunlight/food) available to the organisms in a trophic level is transferred to the next trophic level
-around 90% of the total available energy is lost in various ways
-60% is never taken in by the organisms in the first place
-rest of the available energy(40%) is absorbed = gross productivity
-to the next trophic level, 30% of the total energy available is lost to the next environment when organisms use energy produced from respiration for movement or body heat = respiratory loss
-only 10% of total available energy or 25% of gross productivity becomes biomass–} net productivity= amount of energy available to the next trophic level
-then flow of energy transfer continues at the next trophic level + process starts from beginning
What affects efficiency at producer level?
-producers only convert 1 to 3% of sunlight into chemical energy/biomass due to:
- around 90% of solar energy being reflected, some being transmitted through the leaf + some being an unusable wavelength
- limiting factors of photosynthesis i.e water availability
- energy being used up in photosynthetic reactions
-from the gross production, 20 to 50% is used for energy in respiration + the rest is converted to biomass(net production)
Formula for calculating energy available to the next trophic level
net production= gross production - respiratory loss
What affects efficiency at consumer level?
-convert at most 10% of the biomass in their food to their own organic tissue due to:
- not all biomass of an organism being eaten (passed to decomposers)
- some energy being transferred to the environment as metabolic heat(movement + respiration)
- some parts of food are indigestible so come out as faeces(decomposers)
- excretory materials i.e urine
-only around 0.001% of original total energy from sunlight is received by tertiary consumer
Formula to calculate efficiency of energy transfer between each trophic level
% ecological efficiency= biomass transferred/ biomass intake x100
What is the result of energy loss at each trophic level?
-limits the no. of organisms that can exist in a particular ecosystem
Why is efficiency of energy transfer lower for producer-consumer than consumer-consumer?
-plants contain a greater proportion of indigestible material i.e cellulose in plant cell walls than animals(large proportion of digestible meat)
Human methods to increase productivity of food chains
-herbicides(kill weeds, less competition so crops receive more energy)
-fungicides(kill fungal infections that damage crops, more energy for growth)
-insecticides(less biomass lost from crops)
-natural predators(eat the pest species, crops lose less energy + biomass)
-fertilisers(provide minerals for growth)
-rearing livestock intensely(more energy used for growth)
-controlled abiotic factors i.e watering, warmth
-less trophic level (producers + primary consumer/human)–} more energy transferred into biomass to be eaten by humans
Why is nitrogen essential for plants + animals?
-needed to make amino acids/proteins + nucleic acids(DNA/RNA) for growth
-although 78% of air is nitrogen gas(N2) it needs to be converted into nitrogen compounds by bacteria first to be useable
Nitrogen fixation
-N2 in the atmosphere is converted to ammonia (NH4) by nitrogen fixing bacteria: free-living azotobacter or bacteria in root nodules of legumes, rhizobium –} form a mutualistic relationship with the plants(plant gains AA produced by fixing nitrogen gas, bacteria gain carbohydrates produced by the plant in photosynthesis which is used as energy source)
-bacteria contain nitrogenase which combines N2 with hydrogen(H2) to produce ammonia which can be absorbed + used by plants
Ammonification
-nitrogen containing compounds in dead organisms/faeces and urine are digested by decomposers using saprotrophic external digestion + converted into ammonia which forms ammonium ions
Nitrification
-when ammonium ions are converted nitrogen-containing molecules that can be used by plants
-oxidative reaction that only occurs in well aerated soil
- ammonia dissolves into ammonium ions
- nitrosomonas oxidises ammonium ions into nitrites(NO2-)
- nitrobacter oxidises nitrites into nitrates(highly soluble so more nitrogen can enter plant)
*nitrosomonas + nitrobacter are nitrifying bacteria + chemautrophs(obtain energy from oxidation as electrons enter ETC and lead to ATP formation)
Denitrification
-in the absence of oxygen i.e waterlogged soil pseudomonas converts nitrates in the soil back to nitrogen gas
-bacteria use the nitrates as a source of energy for respiration + nitrogen gas is released, replenishing the atmosphere
-only happens under anaerobic conditions
Nitrogen fixation by non-living processes
-lightning: huge quantities of energy can cause nitrogen to react with oxygen = nitrogen oxide(dissolves in rain + carried to ground)
-Haber process: artificial fertilisers produced from atmospheric nitrogen on an industrial scale
What is succession?
-process by which an ecosystem changes over time as a result of abiotic factors/environmental conditions(lead to biotic changes)
Primary succession vs secondary succession
-primary= occurs on a newly formed/exposed area of land with no soil or organic material present to begin with i.e bare rock
-secondary= occurs on areas of land where soil is present but has no plants/animals i.e forest fire
Causes of primary succession
-volcanoes erupt + deposit lava–} solid igneous rock formed when it cools down
-sand is blown away by wind/deposited by sea = sand dunes
-silt + mud are deposited at river estuaries
-glaciers retreat depositing rubble + exposing rock
Stages of succession: pioneer species
-pioneer species colonise a new environment with hostile abiotic conditions i.e high light intensity + extreme wind, limited water availability as there’s no soil, few minerals or nutrients
-arrive as spores/seeds carried by wind from nearby land or animal droppings
-specialised to cope with harsh conditions:
- ability to produce large quantities of seeds/spores
- seeds that germinate rapidly
- ability to photosynthesise to produce their own energy
- nitrogen fixation to add to mineral content of soil
Examples of pioneer species
-Lichens(made up of fungus + an alga): secrete acid to erode rock and release minerals
-Marram grass: grows on sand dunes near the sea (deep roots, tolerate salty environment)
-moss
Stages of succession: intermediate community
-weathering of the bare rock forms basis of the soil
-when organisms of the pioneer species die and decompose small, organic products called humus –} forms basic soil which helps to retain water + contains minerals including nitrates(less hostile conditions)
-can support growth of new species, secondary colonisers i.e moss + smaller plants, arrive as spores/seeds and can survive + outcompete the pioneer species
-as conditions improve, tertiary colonisers arrive(waxy cuticle to prevent water loss)
-new organisms die + decompose–} adds more organic material and creating soil richer in minerals + retains more water(favourable for small, flowering plants)
Stages of succession: climax community
-relatively stable, long-lasting community that shows very little change over time
-the species that makes up climax community depends on climate
-lower biodiversity at this stage as there is one dominant species
Stages of succession: deflected succession
-succession that is affected by farming or other human activity i.e mowing, grazing, burning crops
-prevents ecosystem from reaching climax community
What is distribution of organisms and how is it measured?
-where individuals are found within an ecosystem(in favoured biotic/abiotic factors)
-measured with line/belt transect(systematic sampling)
What is abundance of organisms and how is that measured?
-no. of individuals in a species present in an area at any given time(affected by immigration/emigration and birth/death)
-measured using frame/point quadrats–} estimated no. in population = no. of individuals in sample/area of sample
-use random sampling with large sample size to increase accuracy
Measuring animal abundance
-animals move too fast for quadrats, must use capture-recapture to estimate population size
-Estimated population size = number of individuals in first sample x
number of individuals in second sample/ number of recaptured marked individuals
-can calculate biodiversity in a habitat using Simpson’s index
