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What does 'fixation' mean?
It means changing energy into a form that can be used by organisms
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How is energy fixed?
Energy is fixed by autotrophs
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What is a photoautotroph? Give examples
- A photoautotroph is an organism that uses photosynthesis to convert light energy and inorganic molecules (H2O and CO2) into complex organic molecules eg glucose, starch, cellulose, etc.
- Examples of photoautotrophs are green plants eg daisy
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What is a chemoautotroph? Give examples
- A chemoautotroph is an organism that uses the energy released from the breakdown of inorganic molecules to synthesise complex molecules
- Examples of chemoautotrophs are bacteria eg Nitrosomonas and Nitrobacter
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What is primary productivity? How can it be measured?
- Primary productivity is the amount of material made by an autotroph in an ecosystem in a given time.
- It can be measure by the biomass of vegetation added to an ecosytem per unit area in a given time eg km2/m/year
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Explain the difference between Gross Primary Productivity and Net Primary Productivity
- Gross Primary productivity is the total primary productivity. Whereas, Net Primary Productivity is the gross primary productivity minus the energy used by the autotrophs during respiration.
- NPP = GPP - energy used in respiration
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What is a producer?
A producer is an organism that can synthesise it's own energy - they are autotrophs
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What is a consumer?
A consumer is an organism that must eat other organisms to obtain their energy and nutrients - they are also called heterotrophs
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What is a primary consumer?
An organism on the trophic level of an ecosystem where herbivores eat plants
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What is a secondary consumer?
An organism on the trophic level of an ecosystem where carnivores eat herbivores
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What is a tertiary consumer?
An organism on the trophic level of an ecosystem where larger carnivores eat smaller carnivores
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What is a herbivore?
A herbivore is an organism that eats plants eg a sheep
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What is a carnivore?
A carnivore is an organism that eats other animals eg lion
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What is an omnivore?
An omnivore is an organism that eats both plants and animals eg humans
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What is a detrivore?
A detrivore is an organism that lives in or on the soil and feeds and gains nutrients from detritus eg worms
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What is a decomposer?
A decomposer is an organism that absorbs nutrients from dead organisms and waste from living organisms, converting them into inorganic molecules eg bacteria and fungi
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What is a trophic level in a food web?
A trophic level is any leve in a food chain or web which energy passes through as it goes through an ecosystem
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What are the roles of producers, consumers and decomposers in the flow of energy in an ecosystem?
- Producers convert light energy into chemical energy via photosynthesis. They are the organisms that introduce the inital amount of energy that will pass through the ecosystem.
- Consumers pass this energy on through up the trophic levels of an ecosystem by eating animals. Only ~10% of the energy is passed on to the next consumer as most is lost through heat.
- Decomposers break down the remains of dead plants and animals, releasing the leftover energy and nutrients back into the ecosytem so they can be used again.
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Approximately how much energy is converted from the sun falling on a plant to energy stored by the plant?
~1%
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How much energy is generally passed on from one trophic level to the next?
~10%
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What type of energy is passed between trophic levels?
Chemical energy
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What energy is lost between the trophic levels (how is it 'lost' from the food chain)?
- Respiration (ultimately lost as heat)
- Movement
- Not all materials being consumed (bones)
- Not all materials being digested (poo)
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How is most energy ultimately lost from the food chain?
As heat
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What is a pyramid of numbers?
In a pyramid of numbers each rectangle represents the number of organisms at each trophic level
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What is a pyramid of biomass?
In a pyramid of biomass each rectangle represents the (dry) mass of the organims at each trophic level
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What is a pyramid of productivity?
A pyramid of productivity shows the flow of energy through the food chain and the production or turnover of biomass at each trophic level
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What units are used in each of these pyramids?
- Numbers - n/a
- Biomass - g/m2Producivity - g/m2/year or J/m2/year
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Explain why pyramids of numbers and biomass can be inverted but pyramids of productivity cannot be inverted if the ecosystem is sustainable
- Pyramids of numbers can be inverted as one autotroph could provide enough energy to support numerous heterotrophs eg one tree can provide for many caterpillars
- Pyramids of biomass can be inverted as well as one autotroph, which can provide enough energy to support many heterotrophs, may have a smaller biomass than all the combined heterotrophs on the next trophic level eg one tree, many bugs
- However, a pyramid of productivity cannot be inverted as if the autotroph has a very small productivity it will not be making enough energy to support the heterotrophs on the following trophic levels
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What are the advantages of using these pyramids in representing energy flow through a food chain or web?
- Numbers - 'numbers' of organisms can be relatively easy to count
- Biomass - shows how much material is present which is a more accurate measure of energy than numbers
- Productivity - Takes account of the rate of production over a period of time (rather than a snapshot like biomass)
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What are the disadvantages of using these pyramids in representing energy flow through a food chain or web?
- Numbers - numbers do not represent all energy available eg one large producer
- Biomass - Does not take account of uneaten body parts, biomass is harder to measure than numbers, does not take into account fast reproducing producers which can sustain many primary consumers
- Productivity - Still need biomass and therefore need dry mass which destroys ecosystem
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