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What does 'fixation' mean?
It means changing energy into a form that can be used by organisms
How is energy fixed?
Energy is fixed by autotrophs
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
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
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
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
What is a producer?
A producer is an organism that can synthesise it's own energy - they are autotrophs
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
What is a primary consumer?
An organism on the trophic level of an ecosystem where herbivores eat plants
What is a secondary consumer?
An organism on the trophic level of an ecosystem where carnivores eat herbivores
What is a tertiary consumer?
An organism on the trophic level of an ecosystem where larger carnivores eat smaller carnivores
What is a herbivore?
A herbivore is an organism that eats plants eg a sheep
What is a carnivore?
A carnivore is an organism that eats other animals eg lion
What is an omnivore?
An omnivore is an organism that eats both plants and animals eg humans
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
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
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
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.
Approximately how much energy is converted from the sun falling on a plant to energy stored by the plant?
How much energy is generally passed on from one trophic level to the next?
What type of energy is passed between trophic levels?
What energy is lost between the trophic levels (how is it 'lost' from the food chain)?
- Respiration (ultimately lost as heat)
- Not all materials being consumed (bones)
- Not all materials being digested (poo)
How is most energy ultimately lost from the food chain?
What is a pyramid of numbers?
In a pyramid of numbers each rectangle represents the number of organisms at each trophic level
What is a pyramid of biomass?
In a pyramid of biomass each rectangle represents the (dry) mass of the organims at each trophic level
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
What units are used in each of these pyramids?
- Numbers - n/a
- Biomass - g/m2Producivity - g/m2/year or J/m2/year
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
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)
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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