Module: Transfer of Energy in Ecosystems
DCI: LS2.B (B) Plants or algae form the lowest level of the food
web. At each link upward in a food web, only a small fraction of the matter
consumed at the lower level is transferred upward to produce growth and release
energy in cellular respiration at the higher level. Given this inefficiency,
there are generally fewer organisms at higher levels of a food web. Some matter
reacts to release energy for life functions, some matter is stored in newly
made structures, and much is discarded. The chemical elements that make up the
molecules of organisms pass through food webs and into and out of the
atmosphere and soil, and they are combined and recombined in different ways. At
each link in an ecosystem, matter and energy are conserved.
PE: HS-LS2-4 Use mathematical representations to support claims for
the cycling of matter and flow of energy among organisms in an ecosystem.
[Clarification
Statement: Emphasis is on using a mathematical model of stored energy in
biomass to describe the transfer of energy from one trophic level to another
and that matter and energy are conserved as matter cycles and energy flows
through ecosystems. Emphasis is on atoms and molecules such as carbon, oxygen,
hydrogen and nitrogen being conserved as they move through an ecosystem.]
[Assessment Boundary: Assessment is limited to proportional reasoning to
describe the cycling of matter and flow of energy.]
The ideas in this standard are:
- the lowest level of the food web is made up of plants and algae (Producers)
- As you move up the food web, only a small amount of the matter consumed at the lower level is transferred upward to produce growth and release energy (through cellular respiration) at the higher level.
- Because the transfer of matter and energy is somewhat inefficient, there need to be fewer organisms at the top of a food web.
- some of the matter from lower levels of the food web reacts to release energy for life functions
- some of the matter is stored in the newly made structures
- much of the matter is discarded
- the chemical elements that make up an organisms molecules pass through food webs and out into the atmosphere and soil
- these elements are combined and recombined in different ways
- at each link in an ecosystem, matter and energy are conserved
We need to keep to a minimum the number of questions which relate directly back to reading a food web diagram. I will provide one here, but really, we should be moving past that and into conceptualizations of the flow of energy from one level of a food web to the next, and the processes by which that transfer of energy takes place.
We can also ask what happens to the matter that is not cycled, or the energy which is not used, etc, and get to the fact that matter and energy are conserved. When they say mathematical model, my guess is that they mean the 10% rule, but since they don't say that, we can't use it exactly like that. We will have to use the idea in a vague, general sense. We can concentrate too, on the atoms of carbon, hydrogen, or oxygen that get moved between organisms and how they are the same atoms, just changing forms as they move from one level to the next.
We can also ask what happens to the matter that is not cycled, or the energy which is not used, etc, and get to the fact that matter and energy are conserved. When they say mathematical model, my guess is that they mean the 10% rule, but since they don't say that, we can't use it exactly like that. We will have to use the idea in a vague, general sense. We can concentrate too, on the atoms of carbon, hydrogen, or oxygen that get moved between organisms and how they are the same atoms, just changing forms as they move from one level to the next.
Possible Questions:
"A food web diagram is provided.
The trophic level which represents the greatest amount of stored energy in the food web includes which of the following organisms?"
correct answer - red oat grass
incorrect answer - wildebeast
"The energy animals need to carry out their life functions is made available to them when which of the following processes takes place?"
correct answer - glucose molecules are broken down and recombined into carbon dioxide and water
incorrect answer - nitrogen gas from the atmosphere is taken in and carried to all of the cells of the body
A question relating the inefficiency of energy transfer to energy conservation might work. Something like...
"As energy is transferred between trophic levels, from producers to primary consumers, to secondary consumers, each level only a small fraction of the available energy is transferred. How can this be reconciled with the concept of conservation of energy?"
* the remaining energy is lost to heat through metabolic processes
- organic systems do not demonstrate the conservation of energy
?
If we want to do some math, we could have a diagram similar to this one.
http://media.web.britannica.com/eb-media/00/95200-004-52061B80.gif
We could leave out some numbers and ask the kids about the missing data.
A question relating the inefficiency of energy transfer to energy conservation might work. Something like...
"As energy is transferred between trophic levels, from producers to primary consumers, to secondary consumers, each level only a small fraction of the available energy is transferred. How can this be reconciled with the concept of conservation of energy?"
* the remaining energy is lost to heat through metabolic processes
- organic systems do not demonstrate the conservation of energy
?
If we want to do some math, we could have a diagram similar to this one.
http://media.web.britannica.com/eb-media/00/95200-004-52061B80.gif
We could leave out some numbers and ask the kids about the missing data.
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