Define ecosystem
a community of animals. plants and bacteria interrelated with the physical and chemical environment,involving abiotic and biotic factors
Define habitat
place where an organism lives
Define population
all organisms of one species who live in the same place at the same time
Define community
all populations of diff species who interact with eachother and live at the same place at the same time
Define niche
role of a species in an ecosystem
impossible for 2 species to occupy exactly the same niche in the same ecosystem
What are the main types of organisms found in a food web?
- producers: plants and some photosynthetic organisms supply chemical energy to all others
- primary consumer = herbivores, eaten by carnivorous secondary consumers
- decomposers : feed on dead animals and wastes
What are some abiotic factors? What can they be influenced by?
What are some examples of factors lethal at both extremes vs one extreme?
- pH, humidity, temperature, pollutant conc
- can be influenced by biotic components e.g. in a rainforest the forest canopy influences temp and humidity
BOTH: pH
ONE: pollutant levels
Why are ecosystems dynamic? What 3 types of changes can occur?
- non living elements change and the living elements grow and die
- CYCLIC: repeat themselves in a rhythm e.g movement of tide or predator + prey fluctuation
- DIRECTIONAL: one direction, tend to last longer than lifetime of the organisms in that ecosystem. e.g. coast erosion
- ERRATIC: no rhythm or constant direction. e.g. lightning and hurricanes
What does biomass consist of? What is recycled, what isnt?
organic components e.g glucose, and inorganic components e.g. ions, but NOT water
materials recycled, energy isn’t
What is each level of a food chain called? What is transferred between these?
trophic level
biomass is transferred
How is biomass lost at each level?
used up in metabolic processes such as respiration, so some is also transferred as heat and materials are lost as carbon dioxide and water
biomass lost as dead organisms and waste products that only become available to decomposers such as fungi and bacteria
many parts are not digestible/consumed for growth e.g. bones, hair, feathers
what is a pyramid of numbers vs a pyramid of biomass?
NUMBERS: used when organisms in a food chain are roughly the same size, and so the area is proportional to the no. of individuals at that level, as an approx for total biomass
BIOMASS: better approach. where area is proportional to DRY MASS of all organisms at that trophic level
What is the method for collecting dry mass? Why is this an issue?
put organisms in oven, periodically find mass. when mass stops reducing, take them out
destructive though, especially bad for endangered species, so ecologists often measure wet mass and calculate dry mass based on previously published data
How do you calculate ecological efficiency?
biomass at higher level / biomass at lower level
x 100
Define nitrogen fixation. What two types of bacteria do this?
Conversion of atmospheric nitrogen into nitrogen containing compounds
Rhizobium in leguminous plants e.g. root nodules = mutualistic
Azotobacter = free living in soil
Define nitrification - which 2 bacteria do this? What does it require?
What type of bacteria are they?
Conversion of ammonia/ammonium ions into nitrite/nitrate ions
NH4+ -> NO2- = done by Nitrosomonas in soil
NO2- -> NO3- = Nitrobacter in soil
Chemoautotrophic
Requires oxygen so only occurs in well aerated soil
What is denitrification? Where does it occur?
Conversion of nitrates into atmospheric nitrogen
Occurs in waterlogged soils where bacteria use nitrates in respiration
What is ammonification?
Decomposition to convert nitrogen containing matter (e.g. nitrogen in soil, or in urea or wastes) into ammonium ions
Bacteria involved in putrefaction of proteins in dead/waste matter
Bacteria and fungi involved in decomposition feed in a different way from animals. What is this called and what are the 3 steps?
Saprotrophically
- Saprotrophs secrete enzymes onto dead and waste material
- Enzymes digest the material into small molecules, which are then absorbed into the saprotrophs body
- Having been absorbed, the molecules are stored or respired to release energy
What are the key processes that add carbon dioxide to the atmosphere and remove it from the atmosphere?
ADD
Respiration in animals and plants
Decomposition of detritus, humus and wastes
Weathering of limestone and chalk adds it to water, which dissolves to form carbonic acid
Combustion of fossil fuels
REMOVE
Terrestrial plants use it in photosynthesis, and aquatic organisms use dissolved carbonates
What is productivity?
Rate of energy transfer through each trophic level in a food chain
What is GPP vs NPP?
GPP: rate at which plants convert light energy into chemical energy
- only some light energy enters LDR, some of this involved in glucose production, and some of this glucose used for growth
NPP: proportion of energy from the Sun available to enter the food chain - the chemical energy in plant biomass after respiratory losses have been taken into account
How do humans increase primary productivity? (7)
- plant crops early to provide a longer growing season, or in light banks
- drought resistant strains bred
- greenhouses provide warmer temps = inc rate of biomass production
- crop rotation stops reduction of inorganic ions in soil
- pest-resistant plants bred, GM, or use of pesticides
- herbicides to kill weeds and dec competition
- fungicides, or breeding or GM -> prevent fungal diseases
How do humans increase secondary productivity? (4)
- young animals invest more energy into growth, so harvesting animals before adulthood decreases energy loss
- selective breeding = improved breeds
- antibiotics = avoid energy loss to pathogens
- zero grazing/keeping indoors = stops movement and keeps constant temp
