Flashcards in F215:03:02 Understanding energy transfer Deck (38):
What is a trophic level?
the level at which an organism feeds in a food chain
What do the arrows on a food chain show?
The direction of energy transfer (not who eats who)
What does a food chain show?
how energy is transferred from one organism to another
Why are food chains of just Producer->primary consumer->secondary consumer ->tertiary consumer usually inaccurate
As within ecosystems, living organisms are usually members of more than one food chain and often feed at different trophic levels in different chains
Better to draw them as a food web
What is lost at each trophic level from a food chain?
energy which is therefore unavailable to the organism at the next trophic level
Give two examples of ways energy is lost
goes to decomposers/ lost as heat
How is energy lost as heat?
At each trophic level, organisms need to carry out life processes e.g respiration which releases molecules like glucose which is eventually (partly) turned into heat
How is energy passed on to decomposers?
Energy remains stored in dead organisms and waste material which is only available to decomposers
What is waste material?
parts of animals and plants that cannot be digested by consumers
What is the effect of energy loss as it flows through the trophic levels?
As there is less energy to sustain living tissues at higher levels of the food chain and so less living tissue can be kept alive.
What happens if organisms are about the same size in a food chain?
It means there will be fewer consumers at higher levels
How do ecologists represent the idea of their being fewer consumers at the higher levels?
They draw a pyramid of numbers
Where the area of each bar in the pyramid is proportional to the number of individuals
What can pyramids be used to represent?
Either food chains or an ecosystem as a whole
Why is counting the number of organisms not always the best method for studying an ecosystem?
As it does not always provide an accurate picture about how much living tissue exists at each level
What is better than a pyramid of numbers when determining how much living tissue exists at each trophic level?
A pyramid of biomass where the area of the bar is proportional to the dry mass of all the organisms at that trophic level
How would an ecologist properly create a pyramid of biomass?
- Collect all the organisms at that trophic level
- put them in an oven at 80 degrees until all the water in them has been evaporated
Why is creating a proper pyramid of biomass often avoided?
As it is highly destructive of the ecosystem being studied
How do ecologists reduce the destructiveness of their studies when creating a pyramid of biomass on an ecosystem?
They measure the wet mass of the organisms and calculate the dry mass on the basis of previously published data
Why are pyramids of biomass not perfect for studying an ecosystem?
As different species may release different amounts of energy per unit mass
If ecologists are wanting to create a set of data to present the amount of energy released per unit mass?
a pyramid of energy
How would an ecologist create a pyramid of energy properly?
Burning the organisms in a calorimeter and working out how much heat energy is released per gram
How do you calculate how much heat energy is released per gram?
from the temperature rise of a known mass of water
Why do ecologists using revert to using pyramids of biomass rather than pyramids of energy?
As it is highly destructive and extremely time consuming
Give two examples of the limitations of pyramids of energy
They only take a snapshot of an ecosystem at one moment in time
Because populations flucuate over time, it may give a distorted idea of the efficiency of energy transfer
What is productivity?
The rate at which energy passes through each trophic level ina food chain
How is productivity represented?
as a pyramid of energy flow
What does productivity give us an idea of?
How much energy is available to the organisms at a particular trophic level, per unit area (usually square metre) in a given amount of time (usually a year)
How is productivity usually measured?
in kilojoules/megajoules of energy per square metre per year
What is the primary productivity?
The productivity of the plants at the base of the food chain
What is a megajoule?
one million joules/ one thousand kilojoules
What is the gross primary productivity?
The rate at which plants convert light energy into chemical energy
What is the net primary productivity?
The remaining energy that is available to the primary consumer after energy has been lost from respiration
What does NPP stand for?
net primary productivity
Explain why ecologists prefer to draw a food web instead of a food chain
To show energy flow through the whole ecosystem rather than through just one food chain
Explain why ecologists prefer to draw a pyramid of energy rather than a pyramid of biomass
Because a pyramid of energy provides a more accurate picture of energy at each trophic level. This is because the dry mass in differnt organisms may release different amounts of energy
Suggest why there are fewer individuals at higher trophic levels in a food chain
Because energy leaves the food chain at each trophic level, so there is less energy available at each successive trophic level meaning fewer and fewer organisms can survive at higher and higher trophic levels
Suggest why most food chains have no more than five stages
Because energy leaves the food chain at each level, and eventually there is not enough energy to sustain individuals at the highest trophic levels