Ecosystems Flashcards
Define ‘Ecosystem’
All the living organisms and all the non-living components in a specific habitat, and their interactions. They are dynamic systems.
Define ‘Abiotic Factor’, giving examples
Abiotic factors describe the effects of the non-living components of an ecosystem, e.g. pH, temperature, soil type etc.
Define ‘Biotic Factor’, giving examples
The ways living organisms can effect each other in an ecosystem, e.g. food supply, predation, disease etc.
Define ‘Producer’
Organisms that supply chemical energy to all other organisms by way of photo/chemisynthesis.
Define ‘Consumer’
Organisms that feed on other organisms (they could be animals or fungi, feeding off plants or animals)
Define ‘Decomposer’
Organisms that feed on waste material or dead organisms
Define ‘Trophic Level’
The level at which and organism feeds in a food chain.
How is energy transferred through ecosystems?
Some energy is lost at each trophic level for the organism to carry out life processes: respiration releases chemical energy that could be converted to heat. Energy in dead organisms and waste material (material that can’t be digested) can only be released by decomposers.
What does the energy loss at each trophic level result in?
If all species in a food chain are the same size, there will be less consumers at the top than there are producers, as there will be less energy to sustain them. We can draw a pyramid of numbers to represent this.
How can we measure the efficiency of energy transfer?
- Draw a pyramid of biomass, where the area of the bar is proportional to the dry mass of all the organisms at that trophic level. However, this is destructive, so can take wet mass and calculate dry mass
- Draw pyramid of energy (as different organisms release different energy per unit mass, so biomass pyramid not ideal). Would have to burn organisms in a calorimeter for this: very destructive and time consuming!
What are the limitations of a) pyramids of number; b) pyramids of biomass; c) pyramids of energy
a) Doesn’t provide an accurate picture of how much living tissue there is at each level
b) Measuring dry mass is very destructive; different species may release different amounts of energy per unit mass
c) Measuring energy is very destructive; they only take a snapshot of an ecosystem in time; population size fluctuates, providing a distorted idea of the efficiency of energy transfer
What is ‘Productivity’?
The rate of flow of energy through each trophic level - can draw a pyramid of energy flow. Gives an idea of how much energy is available to the organisms at a particular trophic level in a given time. Measured in kJ or MJ.
Define ‘Gross Primary Productivity’
The rate at which plants convert light energy into chemical energy.
Define ‘Net Primary Productivity’
As not all the light energy plants convert to chemical energy (GPP) is available to consumers (some used in respiration), the rest is the NPP.
How can humans increase the energy we get from plants (NPP)?
- Light intensity limits photosynthesis, and therefore NPP: more light
- Increase water availability/breed drought resistant crops
- Temperature limits speed of chemical reactions: increase temperature to optimum temperature
- Increase availability of nutrients (would otherwise limit photosynthesis and growth
- Pesticides to stop insects etc. eating our yield!
- Prevent fungal diseases of crop plants by spraying with fungicides/breeding resistant crops
- Kill weeds with herbicides to reduce competition for light, water and nutrients
How can humans manipulate the transfer of energy from producers to consumers?
- More energy goes to growth when young rather in adulthood: harvest animals just before adulthood
- Could treat with steroids to increase growth, but against law in EU
- Selectively breed for faster growth rates, increased egg production and increased milk production
- Give antibiotics to avoid energy loss to pathogens and parasites
- Keep environmental temperature constant and preventing animals from having to walk around to find food: zero grazing
Define ‘Succession’
A directional change in a community of organisms over time
How does primary succession work?
- Algae and lichens begin to live on bare rock: the pioneer community
- Erosion of rock and build up of dead and rotting organisms produces soil for larger plants such as mosses and ferns, replacing the algae and lichens
- Larger plants succeed smaller plants until a final, stable community is reached: the climax community (for UK would be a woodland)
Describe primary succession on sand dunes
- Pioneer plants such as sea rocket colonise sand above high water mark
- Sand builds up around these plants, causing a mini-sand dune
- Plants die, so nutrients accumulate and sand dune grows, allowing bigger plants to settle, e.g. sea coach grass
- More stability and more nutrients results in plants such as marram grass beginning to grow (marram grass traps wind blown sand)
- As sand dune grows, other plants colonise the sand, such as Hare’s-foot clover. Bacteria in root nodules help stabilise dunes by providing nitrates etc, so more plants come in.
What is a line transect?
At regular intervals along a stretched out tape measure, make a note of what species are touching the tape
What is a belt transect?
Interrupted: at regular intervals along a tape, place a quadrat and count
Continuous: Move a quadrat along the tape, counting
How to estimate population size from random sampling data
Population size = Mean number of individuals in each quadrat/Fraction of total habitat area covered by one quadrat
What is the role of decomposers in decomposition?
Bacteria and fungi (decomposers) feed saprotrophically: they excrete enzymes onto dead/waste material which break it down into smaller molecules that the organism then absorbs to store/respire.
-Essential, or energy would remain trapped in dead organisms. Nutrients are recycled too!
Summarise the nitrogen cycle
- Nitrogen in the air, N(2)
- Fixed by nitrogen fixing bacteria to organic nitrogen
- Organic nitrogen (ammonium ions) is absorbed by plants; goes along food chain
- Organic nitrogen is excreted/released on death
- Converted to ammonium by decomposition and ammonification
- Ammonium can be absorbed by plants too
- Ammonium oxidised by bacteria in nitrification to nitrites
- Nitrites oxidised by bacteria to nitrates
- Nitrates run into rivers and streams/absorbed by plants
- Denitrifying bacteria convert nitrates to nitrogen gas and nitrous oxide (N(2)O), as when in anaerobic conditions, can obtain oxygen this way for respiration
- Nitrogen in air can be fixed by lightning, forming nitrogen oxide, which becomes nitrate
- Nitrogen in air can be fixed in Haber process, becoming ammonium ions or nitrate
- Nitrogen in air can be fixed by bacteria in soil, forming organic nitrogen in soil
What are Nitrosomonas?
Chemoautotrophic bacteria that get energy from oxidising ammonium ions to nitrites: only happens in well aerated soils as needs oxygen. (in nitrogen cycle)
What are Nitrobacter?
Chemoautotrophic bacteria that get energy from oxidising nitrites to nitrates: only happens in well aerated soils as needs oxygen. Nitrates can be absorbed by plants
What are Rhizobium?
Nitrogen fixing bacteria which live inside root nodules of leguminous plants. Have a mutualistic relationship: bacteria fix nitrogen for plant; plant provides bacteria with carbon compounds such as glucose. Proteins such as leghaemoglobin keep conditions anaerobic, causing bacteria to use nitrogen reductase to reduce N(2) to ammonium ions
