Performance Benchmark L.12.C.3
Students know how the amount of living matter an environment can support is limited by the
availability of matter, energy, and the ability of the ecosystem to recycle materials. E/S
Energy
All of life’s processes require energy to complete. The energy for these life processes is mostly
derived from the sun. The radiant energy from the sun is captured by plants and converted to
chemical energy (glucose) through photosynthesis. This chemical energy is now available to
other organisms.
Figure 1. From http://www.eia.doe.gov/kids/energyfacts/sources/renewable/biomass.html
Every organism in an ecosystem has a role as either a producer, a consumer or a decomposer.
Primary producers (also called autotrophs) are responsible for converting energy from an
unusable form (radiant energy) to a usable form (chemical energy). Green plants on land and
algae in aquatic environments are the major types of primary producers. A small class of
autotrophic organisms, called chemotrophs, obtains energy by the oxidization of molecules in the
environment. Non-autotrophic organisms are consumers or heterotrophs. Consumers are
organism that must obtain nutrients and energy from other living organisms. The often
overlooked participants in an ecosystem are the decomposers. Decomposers obtain energy from
the remains of dead plants and animals in the process they release the nutrients trapped in the
dead tissues so that they can be then be reused by other members of the ecosystem.
The flow of energy from one organism to another can be modeled with a simple food chain.
Figure 2 shows a simple terrestrial and aquatic food chain. A food chain always begins with the
producer and follows the flow of energy through several levels of consumers. The first order
consumers are herbivores who consume producers. The second order consumer feed on the first
order consumers, etc. However, energy flow through an ecosystem is never as simple as
represented by a food chain because consumers rarely have only one food source. A food web
incorporates many interconnected food chains and provides a better picture of the true flow of
energy in an ecosystem. A food web would also include decomposers as a link in energy
transfer. Figure 3 is a good example of a complex food web. For more information about food
chains and webs see http://www.vtaide.com/png/foodchains.htm.
Figure 3. A more complex food web. Notice that all
organisms have arrows connecting to the decomposers.
From
http://weedeco.msu.montana.edu/class/LRES443/Lectures/
Lecture20/FoodWeb.JPG
Figure 2. An example of simple food chains. From
http://www.anselm.edu/homepage/jpitocch/genbios/53
-10-FoodChains-L.jpg
Another model, of energy flow through an ecosystem is the trophic pyramid. The purpose of a
trophic pyramid is to graphically represent the distribution of biomass or energy among the
different trophic levels of the ecosystem. A trophic level is the position of an organism in an
ecosystem (producer, first order consumer, etc). A pyramid is used as the model because it
shows the decrease in energy available as you go through a food web. The availability of energy
decreases as you travel up the pyramid because only 10% of energy absorbed becomes stored
energy (available to transfer). The other 90% of energy is mostly lost as heat from metabolic
processes and maintenance of daily life functions.
Figure 4. A generic trophic pyramid.
From:
http://en.wikipedia.org/wiki/Energy_
pyramid
Figure 5. A typical trophic pyramid showing the decrease
in energy available as move from one level to the next.
From: http://www.bio.miami.edu/dana/106/106F05_8.html
Matter
Energy flows through an ecosystem
and is ultimately lost to the
environment. Matter, on the other
hand, is recycled. Matter is finite. If
matter was not cycled through the
ecosystem, the supply would have
been exhausted a long time ago. A
simple matter cycle consists of an
exchange of matter between living and
non-living components of an
ecosystem (Figure 6). Organisms
incorporate various elements
(compounds) from the environment
into their bodies. When these
organisms die, their bodies are broken
down by decomposers and the
compounds are released back into the
environment.
Organic
Compounds
Usable as
nutrients
Fossilization
Living
organisms
and organic
matter
Photosynthesis
Organic
Compounds
Usable as
Nutrients
Fossil Fuels
Respiration
Decomposition
Erosion and
Burning of
Fossil
Fuels
InOrganic
Compounds
Usable as
Nutrients
Inorganic
Compounds
Usable as
Nutrients
Weathering
Atmosphere
Soil
Water
The flow of matter through the ecosystem will follow
one of nutrient cycles outlined below.
Minerals in
Rocks
Rock Formation
Figure 6: A generic matter cycle
Nutrient Cycles
Water Cycle
The water cycle, also called the
hydrologic cycle, follows the
continuous path of water. Water
enters the vapor phase through
evaporation and transpiration (the
release of water vapor from plants
and animals). The sun is the main
source of energy that allows the
water to under go a phase change.
The water vapor rises, cools, and
condenses forming clouds. The
water droplets become heavier and
eventually fall as precipitation. A
small portion of the precipitation
will be taken up by the plants and
animals, more will infiltrate the soil,
Figure 7: The water Cycle
entering the water table, with the
From: http://ga.water.usgs.gov/edu/watercycle.html
largest portion of the precipitation
forming runoff on the surface of the
land to drain into streams, rivers, lakes, and ultimately the ocean. The hydrologic cycle is a
continuous process that recycles all the water on the planet.
Carbon Cycle
Carbon dioxide makes up only 0.03% of the
atmosphere but is the major source of carbon for
additional biomass. Carbon dioxide is converted
to organic carbon by photosynthesis in green
plants. Organic carbon is then available to travel
through the food web to eventually be released
back to the atmosphere by cellular respiration and
decomposition. Fossil Fuels are another link in
the carbon cycle. Organic carbon has been trapped
underground for millions of years in the form of
coal, oil, and natural gas. This carbon, in the form
of carbon dioxide, is released back to the
atmosphere by the burning of fossil fuels. Carbon
dioxide that is dissolved in the ocean can be
absorb by animals and temporarily trapped in their
skeletons and shells. It should be noted that
humans are altering the carbon cycle with the
increased use of fossil fuels.
Figure 8: The Carbon Cycle From:
http://www.windows.ucar.edu/earth/Water/co2_cycle.html
Nitrogen Cycle
Nitrogen comprises
approximately 80% of the
atmosphere but is not
accessible to most life forms.
It must be “fixed” before it
can be absorbed. Nitrogenfixing bacteria are responsible
for converting atmospheric
nitrogen into its ionic form,
ammonium. Ammonium is
converted to nitrites and
nitrates. Plants can access
this nitrate. However,
animals must get their
nitrogen from the food that
they eat. Thus, nitrogen flows
through the food web much
like carbon. Nitrogen is
returned back to the
atmosphere through
decomposers and then
denitrifying bacteria.
Figure 9: The Nitrogen Cycle From:
http://en.wikipedia.org/wiki/Nitrogen_cycle
Oxygen Cycle
The oxygen cycle is very similar to the
carbon cycle, but in reverse. Oxygen
comprises approximately 20% of the
atmosphere. Oxygen is removed from the
atmosphere through cellular respiration and
returned to the atmosphere by
photosynthesis. Large amounts of oxygen
are dissolved in large bodies of water.
Figure 10: Oxygen Cycle
From: http://telstar.ote.cmu.edu/environ/m3/s4/cycleOxygen.shtml
Performance Benchmark L.12.C.3
Students know how the amount of living matter an environment can support is limited by the
availability of matter, energy, and the ability of the ecosystem to recycle materials. E/S
Common misconceptions associated with this benchmark:
1. Students incorrectly think plants take in food from the outside environment, and/or
plants get their food from the soil via roots.
Plants internally produce their food through the process of photosynthesis.
Photosynthesis captures light energy, converts and stores that energy in the form of
chemical bonds in glucose. This stored energy is used to carry out metabolic activity
in the plant like the breaking down and the making of biomolecules.
2. Students incorrectly believe individuals higher in the food web have more energy
because energy accumulates up the trophic level.
Trophic pyramids can represent biomass or energy among different trophic levels.
Energy is used by organisms to live and grow. By the time you reach the top of the
pyramid, most of the original energy has been used up by being converted into other
forms of energy. Energy is also lost in the form of heat. Each trophic level only
contributes approximately 10% of original energy obtained to the next trophic level.
For more information access the following websites:
http://www.wsu.edu/DrUniverse/plants.html
http://en.wikipedia.org/wiki/Jan_Baptist_van_Helmont
http://www.eduweb.com/portfolio/earthsystems/food/images/energy_pyramid.gif
3. Students incorrectly believe that there is a starting and ending point for food chains
and webs.
Food chains and food webs should always include decomposers so that the model of
energy and nutrient flow is cyclic rather than linear. In other words, energy and
nutrients are not lock indefinitely in a food web being studied. When organisms die,
defecate, or urinate the material is broken down by decomposers utilize the energy
and return nutrients to the system.
Performance Benchmark L.12.C.3
Students know how the amount of living matter an environment can support is limited by the
availability of matter, energy, and the ability of the ecosystem to recycle materials. E/S
Sample Test Questions
1. Of the energy gained by any trophic level (i.e. producer, primary consumer, secondary
consumer, etc.), what percentage is typically transferred to the next trophic level?
a. 90- 100%
b. 60-70%
c. 30-40%
d. 10-20%
2. Organisms in a higher trophic level in a food web:
a. eat everything that is lower on the food web.
b. have more energy available to them than those lower in the food chain.
c. have less energy available to them than those lower in the food chain.
d. accumulate all of the energy that exists in the organisms that are lower in the food
chain.
3. The diagram above is a food web that shows the relationship among organisms in and
around a pond. One additional biotic factor is needed to make this ecosystem stable is
the presences of
a. producers.
b. herbivores.
c. decomposers.
d. consumers.
4. Which ecological principle is best illustrated by the above diagram?
a. An ecosystem requires a constant source of energy.
b. In an ecosystem, material is constantly cycled among organisms and the
environment.
c. Competition within species results in the strongest organisms surviving.
d. In an ecosystem, then number of producers and consumers are equal.
5. Most food and oxygen in the environment is produced by primary producers through a
process referred to as
a. Respiration
b. Competition
c. Biomass
d. photosynthesis
Performance Benchmark L.12.C.3
Students know how the amount of living matter an environment can support is limited by the
availability of matter, energy, and the ability of the ecosystem to recycle materials. E/S
Answers to Sample Test Questions
1.
2.
3.
4.
5.
(d)
(c)
(c)
(b)
(d)
Performance Benchmark L.12.C.3
Students know how the amount of living matter an environment can support is limited by the
availability of matter, energy, and the ability of the ecosystem to recycle materials. E/S
Intervention Strategies and Resources
The following list of intervention strategies and resources will facilitate student understanding of
this benchmark.
1. Trophic / Food Web Activity
This website allows students to practice placing animals in appropriate trophic levels and
then seeing the completed food web. It includes decomposers and scavengers which are often
overlooked by students.
To access these activities: http://www.gould.edu.au/foodwebs/kids_web.htm
2. Water Cycle Animation
This is a cute animation that illustrates the water cycle. It is lower level but includes
definitions of aquifer, condensation, precipitation, and evaporation.
To access this animation: http://www.epa.gov/safewater/kids/flash/flash_watercycle.html
3. Graphics and text related to the nutrient cycles
This website can be assigned to increase content area literacy. It is appropriate for
average readers. It also has “Enhanced Flash Versions” of its nutrient cycle diagrams. These
animations step through each component of the cycle. This animation may assist visual learners
see the process.
To access these graphics of the nutrient cycle diagrapms:
http://library.thinkquest.org/C007506/cycles.html
4. Lesson Plans for the water cycle and energy transfer.
The lesson titled “Water Hunt” is a classroom simulation. The author states that the
activity uses “everyday objects so students will create a tangible method to investigate world
water distribution.” The learning objective for this activity is for students to “be able to
demonstrate that fresh water is a limited resource.”
The lesson titled Energy Quest is described as a “variation of "Duck, Duck, Goose" that
demonstrates the transfer of energy through trophic levels and emphasizes the interconnection of
organisms within a food web. “ The leaning objective is for students to “be capable of
illustrating the transfer of energy within an ecosystem”
To access this web site: http://www.discoverycreek.org/teachers/curriculum/water_lesson.php