Content Benchmark L.12.C.3
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Students know 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

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 2. An example of simple food chains. From http://www.geneseo.edu/ ~saw3/food%20chain.html

(Click Image to Enlarge) 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

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 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

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 5). 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.

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 5). 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.

Nutrient Cycles

Figure 6: The Water Cycle From: http://ga.water.usgs.gov/edu/watercycle.html

Water Cycles

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, entering the water table, with the 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

Figure 7: The Carbon Cycle From: http://www.windows.ucar.edu/earth/Water/co2_cycle.html

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.

Nitrogen Cycle

Figure 8: The Nitrogen Cycle From: http://www.epa.gov/maia/html/nitrogen.html

Nitrogen comprises approximately 80% of the atmosphere but is not accessible to most life forms. It must be “fixed” before it can be absorbed. Nitrogen-fixing 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.

Oxygen Cycle

Figure 9: Oxygen Cycle From: http://telstar.ote.cmu.edu/environ/m3/s4/cycleOxygen.shtml

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.

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Content 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://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.

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Content Benchmark L.12.C.3

Students know 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^st Item Specification: Explain that different environments have different carrying capacities.

Depth of Knowledge Level 1

1. The following graph shows growth patterns of population over time.

Which line represents a population that reaches a carrying capacity?

1. Line 1
2. Line 2
3. Line 3
4. Line 4

2. Which type of graph represents a population in an environment with limited resources
1. Exponential curve
2. Bell curve
3. Logistic curve
4. Predator/Prey curve

Depth of Knowledge Level 2

3. The following table shows the primary productivity of several biomes. The accompanying graph shows the temperature/precipitation relationship of major biomes.

Biome Productivity Kcal/m2/year Tundra 600 Grassland 2000 Desert 200 Seasonal Forest 6000 Rainforest 9000 Scrubland 1000

(Click Image to Enlarge)

(Graph from:http://www.geology.iastate.edu/gcp/datasets/images/ecosystems.gif)

Based on the data given in the graph and table, which environmental factor contributes to greater biodiversity?

1. Average temperature
2. Available water
3. Plant biomass per meter
4. Average latitude

4. The following table describes data collected on herbivores living in the same habitat.  All four species eat the same food.

Based on the data given, rank the carrying capacity for the herbivore species from lowest to highest.

1. 1–2–3–4
2. 2–3–4–1
3. 3–4–2–1
4. 4–2–1–3

2^nd Item Specification: Identify the factors that affect carrying capacity.

Depth of Knowledge Level 1

5. Which of the following factors is a density independent limiting factor?
1. Competition
2. Disease
3. Drought
4. Predation

6. What happens to a population that exceeds the environmental carrying capacity?
1. Death rate and birth rate remain constant.
2. Birth rate and death rate decrease.
3. Death rate decreases and birth rate increases.
4. Birth rate decreases and death rate increases.

Depth of Knowledge Level 2

7. Graph A shows the increase in sewage waste and a decrease in oxygen content of a lake.  Graph B shows population changes of four species of fish in the lake over the same time period.

(Modified from Examgen 4.3)

Which of the following is a plausible conclusion drawn from the above data?

1. The carp were tolerant of the water quality changes. Therefore, the population was able to grow due to decreased competition.
2. The walleye were more tolerant of the water quality changes and the population increased from lowered competition from the carp.
3. The trout are intolerant of water quality changes but the population remained stable.
4. The whitefish were intolerant of water quality changes and the population grew.

8. Which of the following would NOT be a limiting factor to the size of a large, dense population?
1. Competition for food, water, space, and sunlight.
2. Predation by abundant predators in the area.
3. Surviving a natural disaster such as a hurricane.
4. Spreading of parasites and other disease agents

3^rd Item Specification: Predict the result of changing a factor on the carrying capacity of an ecosystem.

Depth of Knowledge Level 1

9. The moose and wolf populations of Isle Royal National Park are one of the most studied predator/prey relationships. What would be a long term effect of removing the wolves from the park? The moose population will
1. increase dramatically due to the lack of predators.
2. die off due to disease because the wolves are not removing the sick individuals
3. decrease initially due to disease and then increase dramatically because of lack of predators.
4. increase initially due to lack of predators then decrease due to overgrazing.

10. When Rapa Nui (Easter Island) was colonized by a small number of humans it was covered with trees and abundant food types.   Within a thousand years the Rapa Nui population disappeared and the island was grassy. Which of the following is the MOST plausible cause of the population crash?  As the population increased,
1. the different groups warred with each other reducing the overall population.
2. the people cut down the trees for shelter and overused the food available faster than the resources were replenished.
3. the people used the island as a resting place before moving onto other islands.
4. new immigrants brought a disease with them that caused a fatal epidemic.

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Content Benchmark L.12.C.3

Students know 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. C, DOK Level 1
2. C, DOK Level 1
3. B, DOK Level 2
4. B, DOK Level 2
5. C, DOK Level 1
6. D, DOK Level 1
7. A, DOK Level 2
8. C, DOK Level 2
9. D, DOK Level 1
10. B, DOK Level 1

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Content 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 is a list of intervention strategies and resources that 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. 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:
h ttp://library.thinkquest.org/C007506/cycles.html

3. 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

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

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