E2.3 Darlene RocheClarkston Schools

Biogeochemical Cycles

Content Statement:E2.3 The Earth is a system containing essentially a fixed amount of each stable chemicalatom or element. Most elements can exist in several different states and chemical forms;they move within and between the geosphere, atmosphere, hydrosphere, and biosphere aspart of the Earth system. The movements can be slow or rapid. Elements andcompounds have significant impacts on the biosphere and have important impacts onhuman health.

E2.3A Explain how carbon exists in different forms such as limestone (rock),carbon dioxide (gas), carbonic acid (water), and animals (life) within the EarthSystem and how those forms can be beneficial or harmful to humans.

E2.3b Explain why small amounts of some chemical forms may be beneficial forlife but are poisonous in large quantities (e.g., dead zone in the Gulf of Mexico,Lake Nyos in Africa, fluoride in drinking water).

E2.3c Explain how the nitrogen cycle is part of the Earth system

E2.3d Explain how carbon moves through the Earth system (including thegeosphere) and how it may benefit (e.g.,improve soils for agriculture) or harm(e.g., act as a pollutant) society

Question To Be Investigated:What are some important chemical elements that move within the Earth system and howdoes their movement effect living things?

Background Information:

CARBON CYCLECarbon is an element. It is part of oceans, air, rocks, soil and all living things. Carbon

doesn’t stay is one place. It is always on the move!

Carbon moves from the atmosphere to plants.In the atmosphere, carbon is attached to oxygen in a gas called carbon dioxide(CO2). With the help of the Sun, through the process of photosynthesis, carbondioxide is pulled from the air to make plant food from carbon.

Carbon moves from plants to animals.Through food chains, the carbon that is in plants moves to the animals that eatthem. Animals that eat other animals get the carbon from their food too.

Carbon moves from plants and animals to the ground.When plants and animals die, their bodies, wood and leaves decay bringing the

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carbon into the ground. Some becomes buried miles underground and willbecome fossil fuels in millions and millions of years.

Carbon moves fromliving things to theatmosphere.Each time you exhale,you are releasing carbondioxide gas (CO2) intothe atmosphere. Animalsand plants get rid ofcarbon dioxide gasthrough a process calledrespiration.

Carbon moves fromfossil fuels to theatmosphere when fuelsare burned.When humans burnfossil fuels to powerfactories, power plants,cars and trucks, most ofthe carbon quickly enters

the atmosphere as carbon dioxide gas. Each year, five and a half billion tons ofcarbon is released by burning fossil fuels. That’s the weight of 100 million adultAfrican elephants! Of the huge amount of carbon that is released from fuels, 3.3billion tons enters the atmosphere and most of the rest becomes dissolved inseawater.

Carbon moves from the atmosphere to the oceans.The oceans, and other bodies of water, soak up some carbon from the atmosphere.Animals that live in the ocean use the carbon to build their skeletons and shells.

Carbon dioxide is a greenhouse gas and traps heat in the atmosphere. Without it andother greenhouse gases, Earth would be a frozen world. But humans have burned somuch fuel that there is about 30% more carbon dioxide in the air today than there wasabout 150 years ago. The atmosphere has not held this much carbon for at least 420,000years according to data from ice cores. More greenhouse gasses such as carbon dioxide inour atmosphere are causing our planet to become warmer.

Carbon moves through our planet over longer time scales as well. For example, overmillions of years weathering of rocks on land may add carbon to surface water whicheventually runs off to the ocean. Chemical weathering of silicate minerals, in particular,can have an effect on the amount of carbon dioxide in the atmosphere. Additionally, overlong time scales, carbon is removed from seawater when the shells and bones of marineanimals and plankton collect on the sea floor. These shells and bones are made oflimestone, which contains carbon. When they are deposited on the sea floor, carbon isstored from the rest of the carbon cycle for some amount of time. The amount of

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limestone deposited in the ocean depends somewhat on the amount of warm, tropical,shallow oceans on the planet because this is where prolific limestone-producingorganisms such as corals live. The carbon can be released back to the atmosphere if thelimestone melts or is metamorphosed in a subduction zone

Windows to the Universe, at http://www.windows.ucar.edu/ at the University Corporationfor Atmospheric Research (UCAR). ©1995-1999, 2000

NITROGEN CYCLENitrogen is an element that is found in both the living portion of our planet and

the inorganic parts of the Earth system. The nitrogen cycle is one of the biogeochemicalcycles and is very important for ecosystems. Nitrogen moves slowly through the cycleand is stored in reservoirs such as the atmosphere, living organisms, soils, and oceansalong its way.

Most of the nitrogen on Earth is in the atmosphere. Approximately 80% of themolecules in Earth’s atmosphere are made of two nitrogen atoms bonded together (N2).

All plants and animals neednitrogen to make amino acids,proteins and DNA, but thenitrogen in the atmosphere is notin a form that they can use. Themolecules of nitrogen in theatmosphere can become usablefor living things when they arebroken apart during lightningstrikes or fires, by certain typesof bacteria, or by bacteriaassociated with legume plants.Other plants get the nitrogen theyneed from the soils or water inwhich they live mostly in theform of inorganic nitrate (NO3-).Nitrogen is a limiting factor forplant growth. Animals get thenitrogen they need by consumingplants or other animals thatcontain organic molecules

composed partially of nitrogen. When organisms die, their bodies decompose bringingthe nitrogen into soil on land or into the oceans. As dead plants and animals decompose,nitrogen is converted into inorganic forms such as ammonium salts (NH4+ ) by a processcalled mineralization. The ammonium salts are absorbed onto clay in the soil and thenchemically altered by bacteria into nitrite (NO2- ) and then nitrate (NO3- ). Nitrate is theform commonly used by plants. It is easily dissolved in water and leached from the soil

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system. Dissolved nitrate can be returned to the atmosphere by certain bacteria in aprocess called denitrification.

Certain actions of humans are causing changes to the nitrogen cycle and theamount of nitrogen that is stored in reservoirs. The use of nitrogen-rich fertilizers cancause nutrient leaching in nearby waterways as nitrates from the fertilizer wash intostreams and ponds. The increased nitrate levels cause plants to grow rapidly until theyuse up the nitrate supply and die. The number of herbivores will increase when the plantsupply increases and then the herbivores are left without a food source when the plantsdie. In this way, changes in nutrient supply will affect the entire food chain. Additionally,humans are altering the nitrogen cycle by burning fossil fuels and forests, which releasesvarious solid forms of nitrogen. Farming also affects the nitrogen cycle. The wasteassociated with livestock farming releases a large amount of nitrogen into soil and water.In the same way, sewage waste adds nitrogen to soils and water.

"Climate Discovery Teacher's Guide." 2005. University Corporation for AtmosphericResearch. 20 Jun 2007 at http://www.eo.ucar.edu/educators/ClimateDiscovery/ESS.htm

Windows to the Universe: The Nitrogen Cyclehttp://www.windows.ucar.edu/tour/link=/earth/Atmosphere/overview.html

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ACTIVITY 1: Introducing the Global Carbon CycleAdapted from Utah State Office of Education, Curriculum Section, Salt Lake City, Utah,84111.http://www.wested.org/werc/earthsystems/biology/globalcarbon.html

Summary: This activity could be used to introduce the carbon cycle. It is an inquirylesson designed to model the flow of a carbon atom as it travels through the carbon cycle.

Duration: One class period.

Category: Inquiry

Materials, equipment and/or facilities:large sheet of paper, colored markers, white 4 x 6 index cards (3 per group).

Prerequisite Instruction:Before this activity, introduce the concepts of flux and reservoir.Reservoir- global locationFlux- a change

Teaching and Learning Strategies:Ensure inquiry: Students will develop independent group charts illustrating the carboncycle. Teachers should not feel the need to answer all their questions, let the studentsdiscover their own answers. Teachers can use student feedback to assess prior knowledgeand misconceptions. When helping students, teachers can stimulate the thought processby answering student questions with questions.

Problem: Speculate on possible pathways a carbon atom might follow over a short andlong time and possible reservoirs where the carbon atom might be found.

Procedure:

1. Divide students into groups of 3, and provide them with a set of the materialslisted.

2. Students should label each card with a possible “reservoir” where they think a largeamount of carbon would be found in the Earth system.

3. After index cards are labeled and filled in, have students decide which of thereservoirs represents the largest and smallest reservoir of carbon atoms on aglobal scale. Write the phrase 'most carbon', and 'least carbon' on that card.

4. Next, have the students attach the three cards to a large piece of paper. Arrange thecards so they are roughly equally spaced from the sides of the paper.

5. Students should realize that a carbon atom can move from one reservoir to another.A carbon flux can be indicated by drawing an arrow from one reservoir to another

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and writing down the process that moved the carbon atom. Students should nowdraw in their arrows and label the arrows indicating the process that the carbonatom might have to go through in order to move from one of their reservoirs to theother.

Summary of Learning:

6. Have students share their observations by taping their group chart on the board.Compare the different charts. Emphasize the similarities among the chartsrather than just differences. Important answers to include are as follows:

Table 1: Some carbon-containing substances and their global locations

Common carbon-containing substancesMajor GlobalLocations

carbon dioxide atmosphere

carbon dioxide (dissolved) hydrosphere

plants biosphere

animals biosphere

Rocks/minerals/soil geosphere

Fossil fuels geosphere

7. Use these similar answers to begin to create a large flow diagram on the board oroverhead projector.

8. Now, have the class identify and discuss different carbon fluxes and add thosearrows and processes to the diagram on the board. Some likely examples include:

fossil fuels(burning) atmosphereatmosphere (photosynthesis) plantsplants & animals (respiration) atmosphereland- (acid rain attack on carbonates)- atmospheredead plants & animals(decomposition)soilatmosphere (dissolving) ocean

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plants(digestion) animalsanimals (create waste) soildecomposed organic materials (heat, pressure, time) fossil fuels

Be sure to point out the relationships between the different earth spheres.

9. Next have students identify the reservoir with the most and least amount ofcarbon. The actual ranking is:

1. oceans (including mid and deep waters)

2. land (soil/rocks/fossil fuels)

3. atmosphere

ASSESSMENT:

Students create their own diagram showing the carbon cycle.

(Technology option: students use the Inspiration computer program or Microsoft word tocreate the diagram)

REINFORCEMENT: Students who require extra review can go to the followingwebsite to play the Carbon Cycle Game.

http://www.windows.ucar.edu/earth/climate/carbon_cycle.html

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ACTIVITY 2: Carbon Sources and Sinks LabAdapted from "Climate Discovery Teacher's Guide." 2005. University Corporation for AtmosphericResearch. 20 Jun 2007 at http://www.eo.ucar.edu/educators/ClimateDiscovery/ESS.htm

Summary: Students will use a chemical indicator (Bromothymol blue) to detect thepresence of carbon dioxide and investigate ways that carbon dioxide moves into and outof the atmosphere.

Key Concepts When dissolved in water, carbon dioxide forms a weak acid, called carbonic

acid, which can be detected by the chemical bromothymol blue (BTB). Carbon dioxide is an important greenhouse gas. Because carbon cycles through the Earth system, carbon dioxide is constantly

moving into and out of the atmosphere. Anything that releases CO2 into the atmosphere (living, dead, or non-living) is

considered a source. Anything that absorbs and holds CO2 from the air or water is considered a

sink. Currently, more carbon dioxide is moving into the atmosphere than out of the

atmosphere.

Time:Preparation: 40 minTeaching: 40 minDiscussion: 30 min

Materials for TeacherBalloon filled with automobile exhaust (see Advanced Preparation)BeakerBromothymol blue (BTB)Cotton ballStraw

Materials for Student Teams:Test tube rack Masking tapeSix test tubes Aluminum foilOne hole stopper with tubing attached Baking sodaVinegar Cotton ballsBottle of BTB working solution StrawsSprig of Elodea (available in pet stores)Marker

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Safety goggles for protection in case of splash or glass breakage

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Advanced Preparation This activity has significant set up time. Part 3 will require set up the previous day.

Part 5 (fossil fuels) will be done as a demonstration as it involves automobileexhaust which contains carbon monoxide (CO).

Make BTB working solution at concentration according to product directions. Preparation of Part 3 Since the set-up for Part 3 will need to sit overnight, either students can put it together

during class and note results the next day, or you can prepare this portion for studentsthe day before. Directions for the set-up are in the Part 3 section on the followingpage.

Procedure for collecting automobile exhaust (for Part 5):1. Important note: Carbon monoxide is an odorless, moderately toxic, poisonous,

and flammable gas. DO NOT have students participate in filling the balloonswith car exhaust. An adult assistant (or two) is necessary, however.

2. Blow up and allow the balloons to deflate. This will stretch the rubber and makethem easier to fill with the relatively low-pressure exhaust.

3. Prepare a cone to collect the car exhaust by rolling up a manila folderlengthwise. One end must be larger than the opening for the car’s tail pipe andthe other end must be small enough for the balloon to fit over it.

4. Use plenty of tape to hold the cone in shape and to make the sides of the conefairly airtight. Note: the paper funnel will work for several fillings withoutburning. DO NOT use a plastic funnel. As the exhaust pipe heats up, the plasticmay melt. You may use a metal funnel, but be VERY careful to avoid any skincontact with the hot metal.

5. Have an assistant turn on the car (make sure brake is on).6. Put the balloon on the small end of the cone.7. Using the heat resistant mitts, approach the exhaust pipe from the side. Place the

large end of the cone over the tail pipe. Use the gloved hand to help form a sealbetween the cone and the exhaust pipe. DO NOT BREATHE THE EXHAUST.The balloon should fill quickly; if not, have your assistant step lightly on theaccelerator.

8. When the balloon is filled, have an assistant use a twist tie or two to tightly sealthe balloon. Do this by twisting the neck several times and doubling it overonce, then place the twist tie around the constricted area.

9. You will want to have at least one balloon for each demonstration. It is useful toprepare a few extra filled balloons.

Background InformationCarbon dioxide (CO2) has a characteristic that enables students to detect it in a

classroom setting. When dissolved in water, carbon dioxide forms a weak acid, calledcarbonic acid. The chemical bromothymol blue (BTB) is a sensitive indicator of thepresence of acid. When gas containing CO2 is bubbled through a BTB solution, carbonicacid forms and the indicator turns from dark blue to green, yellow, or very pale yellowdepending on the CO2 concentration (lighter colors mean higher concentrations).

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Carbon dioxide (CO2) provides the bubble in your soda pop and the “rise” in yourbaked goods. But it is also a very significant greenhouse gas. CO2 is important inmaintaining the earth’s average temperature of about 15°C (59°F). The CO2 trapsinfrared energy emitted from the earth’s surface and warms the atmosphere. Withoutwater vapor, CO2, and methane (the three most important naturally produced greenhousegases), the earth’s surface would be about -18°C (0°F). At this temperature, it is doubtfulthat complex life as we know it would ever have evolved.

Anything that releases CO2 into the atmosphere (living, dead, or non-living) isconsidered a source. Anything that absorbs and holds CO2 from the air or water isconsidered a sink (because, like a sink in your home, it acts as a “holding reservoir”)Over geologic time, CO2 sources and sinks generally balance. In today’s atmosphere,however, CO2 levels are climbing in a dramatic and easily measurable fashion, providingevidence that there are now more CO2 sources than sinks.

Teacher directions for Part 5: Are Fossil Fuels a Source of CO2?(Teacher demonstration)

1. Instructor fills the beaker approximately 1/3 full of BTB2. Instructor takes the exhaust filled balloon, carefully untwist the tie while

holding the neck of the balloon so that the gas does not escape. Twist andpinch the neck of the balloon to prevent air from escaping, but don’t tie it.

3. While still preventing the gas from escaping, insert a straw into the neck ofthe balloon up to the twisted portion. Seal the opening of the balloon tightly toone side by pinching it off with fingers. (You may need to practice this a fewtimes with a regular air-filled balloon.)

4. Insert the straw into beaker.5. Insert a cotton ball at the top of the beaker to help hold the straw steady.6. Gently release air from the balloon by slowly untwisting the neck. Allow the

gas to bubble out at a steady rate until the balloon is empty.7. Provide each group with a sample of BTB from the beaker in their test tube

marked ‘E’ for comparison with the other test tubes.8. Discuss what happened.

Summarizing and Reflecting:Use the Key Concepts to summarize and lead students into the Analysis andConclusion questions.

Extension:Ask students to devise their own experiment to test other sources and sinks of carbondioxide (e.g. carbonated beverages, lime based chalk)

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Student Record Form Name_____________________Date________________

Carbon Dioxide Sources and Sinks

What’s carbon dioxide?Carbon dioxide (CO2) provides the bubble in your soda pop and the “rise” in your bakedgoods. But it is also a very significant greenhouse gas. CO2 is important in maintainingthe earth’s average temperature of about 15°C (59°F). The CO2 traps infrared energyemitted from the earth’s surface and warms the atmosphere. Currently, the amount ofcarbon dioxide and other greenhouses gasses in the atmosphere is increasing causingglobal warming. In this activity you will discover some of the ways that carbon dioxidegets into and out of the atmosphere.

What you’ll need:Six test tubes and a rack Cotton ballsOne hole stopper with tubing attached StrawsBaking soda Bottle of BTB working solutionVinegar Sprig of Elodea (a water plant)Aluminum foil Masking tape and a markerSafety goggles

Part 1: Detecting CO2 Gas1. Use a small piece of masking tape to label two of the test tubes A and B (a

third will be unlabeled). Fill tubes A and B approximately 1/3 full with theBTB solution. (Tube A will be the control, tube B will be the treatment.) Placethe tubes in the rack.

2. Fill an unlabeled tube approximately 1/4 full of vinegar.3. Using the foil, make a small “boat” (small enough to easily fit into the test

tube and float on the vinegar) and fill it 1/2 full of baking soda.4. Carefully slide the foil boat inside the unlabeled vinegar test tube (it is useful

to tilt the tube at an angle to do this) and plug the vinegar tube with thestopper and tubing.

5. Place the free end of the tubing into tube B. Make sure that the end of thetubing reaches the bottom.

6. Place a cotton ball into the neck of tube B.7. Mix the vinegar and soda together by GENTLY swirling the tube from side-

to-side. Don’t shake it upside down! Gas bubbles will begin to bubble rapidlyout of the tubing into the BTB solution in tube B.

8. After a minute or so, compare the color of tubes A and B.

What happened?__________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

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Part 2: Are animals a source of CO2?1. Fill a test tube C approximately 1/3 full of BTB2. Place a straw in the test tube and place a cotton ball in the test tube opening.3. Gently BLOW in the straw. DO NOT draw fluid up into straw!4. Note the color change.

What happened?________________________________________________________________________________________________________________________________________________________________________________________

Part 3: Are plants a source of CO2?1. Fill test tube D approximately 1/3 full of BTB2. Place a sprig of Elodea into the test tube (Use a pencil to push it all the way

into the bottom of the tube)3. Wrap the tube in foil so that no light can get in.4. Place in test tube rack and leave for at least 24 hours.5. Unwrap the foil and note the color change.

What happened?________________________________________________________________________________________________________________________________________________________________________________________

Part 4: Are plants a sink for CO2?1. Using the now-unwrapped test tube with Elodea from Part 3, leave in the light

and observe the BTB color change.

What happened?________________________________________________________________________________________________________________________________________________________________________________________

Part 5: Are Fossil Fuels a Source of CO2? (Teacher demonstration)1. Observe the teacher’s procedure using the balloon filled with car exhaust.2. Obtain a sample from the beaker for your test tube marked “E”3. Compare your test tube “E” with the other test tubes.

What happened?________________________________________________________________________________________________________________________________________________________________________________________

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ANALYSIS & CONCLUSIONS:

1. After finishing all five parts of this activity, compare the colors in all thetubes. Are they different? If so, why?____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

2. Discuss the test results. What are some sources and sinks of carbon dioxide?____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

3. If you wished to reduce the amount of increase in the atmosphere, whichsource would be most important to control? Explain why.____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

4. Would there be problems with such controls? If so, what might they be?____________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________

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ACTIVITY 3: Introducing the Nitrogen CycleClimate Discovery Teacher's Guide." 2005. University Corporation for Atmospheric Research. 20 Jun 2007at http://www.eo.ucar.edu/educators/ClimateDiscovery/ESS_lesson2_10.19.05.pdf

Traveling NitrogenLearning GoalsStudents will

Learn that nitrogen cycles indefinitely through the Earth system and willunderstand the places that it is found on Earth.

Understand that nitrogen is essential for living things. Learn that the cycle is complex and nonlinear traveling between organisms

and the physical environment.

What Students Do in this LessonStudents play the role of nitrogen atoms traveling through the nitrogen cycle to gainunderstanding of the varied pathways through the cycle and the relevance of nitrogen toliving things.

Key Concepts Nitrogen is an element that is found in both the living portion of our planet

and the inorganic parts of the Earth system. Nitrogen cycles ceaselessly through the Earth system. Nitrogen atoms do not always take the same path through the system. There

are many potential routes. There are many ways that humans cause modifications to the nitrogen cycle

(including use of fertilizers, burning of fossil fuels, and livestock farming)Time:

Preparation: 15 minTeaching: 30 minAssessment: 20 min

Materials for Class11 DiceDice Codes (see website or printed materials)Signs with station names (see Advanced Preparation)11 small rubber stamps11 ink pads

Materials for Students:Passport Student Page (see website or printed materials)Pen or pencilLined paper

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Advanced Preparation**If you do not have the printed materials for this content expectation, the Dice Codesand Passport Student Page can be found at the following website:http://www.eo.ucar.edu/educators/ClimateDiscovery/ESS_lesson2_10.19.05.pdf

Make large reservoir signs for: atmosphere, surface water, rainwater,groundwater, fertilizers, soils, ocean, animal waste, dead plants and animals,live plants, live animals.

Print Dice Codes for reservoir stations and cut apart. Set up stations around the classroom (or outside). For each station, supply the

appropriate reservoir sign, dice codes, a die, inkpad, and stamp. Go around the room with the Key to Stamps sheet and stamp each reservoir so

that you know which stamp corresponds with which reservoir. Copy Passport Student Page for all students.

Introducing the Lesson Introduce nitrogen. Survey student knowledge. Where is nitrogen found on

Earth? Does it move from place to place or stay still? Why is it important?Explain that nitrogen travels with the help of bacteria, water, lightning, plantsand animals and that the class is going to discover how nitrogen travels.

You may want to have students read the Windows to the Universe pageentitled The Nitrogen Cycle either prior to or following the lessonhttp://www.windows.ucar.edu/tour/link=/earth/Life/nitrogen_cycle.html

Facilitating the Lesson Show the nitrogen reservoir signs around the room and explain that these are

the places to which nitrogen can travel. These places are called reservoirs. Tell students that for this activity they are each playing the role of a nitrogen

atom. They will travel through the nitrogen cycle (i.e., to different stationsaround the room) based on rolling dice. Tell students that they will each carrya nitrogen passport with them and stamp it each time they get to a nitrogenreservoir station. Then toss the die at the reservoir to find out what your nextdestination will be. Write a note in the passport to indicate how you aregetting from one place to another based on what the die says.

Spread students so that there are 2 or three at each station and allow them tostart traveling with their Passport Student Page by rolling the die at theirstations.

Summarizing and Reflecting Once all student shave traveled enough times to fill in their entire Student

Page, facilitate a group discussion of where they went and how they got there. Create a class diagram or chart to describe the Nitrogen cycle.

AssessmentHave students write a paragraph about their trip through the nitrogen cycle. Includeinformation about (1) where they went, and (2) how they got to each destination.

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ACTIVITY 4: Nitrogen Fixation InvestigationAdapted from Errington, Barbara. "Nitrogen Fixation, OR What a Gas!." Access Excellence ActivitiesExchange. 1995. The National Health Museum. 20 Jun 2007http://www.accessexcellence.org/AE/AEPC/WWC/1995/nitrogen.html

Summary: This is a long term project designed to illustrate nitrogen fixation and thesymbiotic relationship of organisms. Students gain skill in the design, implementationand reporting of a scientific research project using the scientific method. Specifically,students will set up an experiment to determine what effect adding Rhizobium bacteria tolegume seeds would have on plant growth.

Background Information for teacher:Nitrogen is the major component of Earth's atmosphere. It enters the food chain by

means of nitrogen-fixing bacteria and algae in the soil. This nitrogen which has been'fixed' is now available for plants to absorb. These types of bacteria form a symbioticrelationship with legumes--these types of plants are very useful because the nitrogenfixation enriches the soil and acts as a 'natural' fertilizer. The nitrogen-fixing bacteriaform nitrates out of the atmospheric nitrogen which can be taken up and dissolved in soilwater by the roots of plants. Then, the nitrates are incorporated by the plants to formproteins, which can then be spread through the food chain. When organisms excretewastes, nitrogen is released into the environment. Also, whenever an organism dies,decomposers break down the corpse into nitrogen in the form of ammonia. This nitrogencan then be used again by nitrifying bacteria to fix nitrogen for the plants.

Prerequisite Instruction:Students should be familiar with the concepts of symbiosis and the nitrogen cycle.

Duration:One class period for set-up6-8 weeks for plant growthOne class period for recording and analyzing class data and completing lab report.

Materials and equipment (for each student group)1. Two 12.5 cm plastic pots (If the pots are not new, wash used ones with a 10% bleach

solution)2. Masking tape or permanent marker for labeling pots3. Vermiculite, enough to fill the pots4. Six legume seeds (a variety of legumes may be used: soybeans, bush-type lima, or

peas)5. Commercial Rhizobium (Check seed and feed stores or garden centers for a product

called Inoculum. If it is not available in your area, Rhizobium may be ordered fromany biological supply house.)

6. Plastic wrap7. Nitrogen-free nutrients (see teacher instructions)8. Distilled water

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Teacher Instructions:1. Start with a brief discussion on the types of symbiosis by showing visuals such as

transparencies or slides depicting the various relationships.

2. Review the Nitrogen cycle with students. Discuss the idea that Nitrogen is criticalfor plants and animals, but is found mainly in the atmosphere in a form that theycannot use. You may want to model the strong triple covalent bond that makes anN2 molecule so difficult to break apart. Try using 3 identical springs and showingthe difference in strength it takes to pull on the opposite ends of one spring, twosprings and then 3 springs. (You may need to dramatize the efforts needed,depending on the elastic strength of your springs.). Follow up with a discussionabout how plants might be able to get usable forms of nitrogen from the air.

3. Inform students that Rhizobium is a bacterium that is not harmful to humans orpets, but will cause legume roots to form nodules. Tell the students: "The purposeof our investigation will be to find out what effect bacterial interactions have onplants of the bean family."

4. Ask students: "How can we see if a plant is affected by the nodules?" Answerswill vary, but get to factors such as height and weight of a plant as it growscompared to the growth of plants that do not have the nodules.

5. Elicit from students a probable hypothesis as to the effect of the nodules on plantgrowth.

6. After lab setup, students are to state their hypothesis, procedures, data table, etc.

Post-lab1. Place average data from each lab team on board and determine overall class

results. Discuss significant deviations, review scientific error, use of larger samplesize, and other important scientific aspects of the experiment.

2. Have students suggest answers to the questions and discuss.

Optional follow up:Remove the nodules from the plant roots and prepare a Gram stain on the bacteria. Havestudents observe under the microscope.

Directions for Nitrogen-free nutrients0.2g dihydrogen phosphate0.8g potassium monohydrogen phosphate0.2g magnesium sulfate0.1g calcium sulfate0.01g ferric sulfate

Combine the above minerals and store in a covered container. Instruct students to add 1.3grams to one liter of distilled water.

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Student InstructionsNitrogen Fixation, OR What a Gas!

Background:

The environment of plant roots is composed of many types of organisms includingbacteria, fungi, and invertebrates. To survive, plants have evolved ways to interact withthese organisms ranging from defense mechanisms against pathogens to symbioticrelationships that are mutually beneficial.

Objectives:

To describe and explain the importance of nitrogen fixationTo investigate the symbiotic relationship between bacteria and plant rootsTo gain skill in using the scientific method

Problem:

What is the effect of nitrogen fixation via a symbiotic relationship with bacteria on thelength and weight of a selected legume plant?

Materials and Equipment:

1. Two 12.5 cm plastic pots2. Vermiculite, enough to fill the pots3. Six legume seeds4. CommercialRhizobium5. Nitrogen-free nutrients6. Masking tape or permanent marker for labeling pots7. Distilled water (8-12 liters)8. Plastic wrap

Procedure:

1. Label one of your pots "with" and the other pot "without".2. Fill each pot with equal amounts of vermiculite.3. Plant three seeds 2 cm deep in "without" pot.4. Sprinkle a small amount of Rhizobium on three seeds and plant 2 cm deep in the

“with” pot5. Water both pots with distilled water and cover with plastic wrap.6. Leave covered and do not remove plastic until seeds germinate.7. After the first leaves appear, uncover and water with a solution containing 1.3 grams

of nitrogen-free nutrients to one liter of distilled water.8. After six to eight weeks, remove plants from pots, taking care not to disturb nodules,

and measure both the height and weight of each plant.

Nitrogen Fixation Data Sheet

Name Date Hour

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Hypothesis

Data Table

Conclusions:

Questions(answer on separate sheet of paper):

1. What possible error sources were there in this experiment?

2. How does Rhizobium enter the root system?

3. How could we determine how much nitrogen-based fertilizer would be needed to equalthe effect of the bacterium?

Activity 5: Researching how Human Interactions can Influence Chemical Cycles

Summary: Students will work in groups to research real-world environmental situationsthat are created by an imbalance of chemical elements within the Earth System. Eachgroup will present their results in a PowerPoint presentation.

Materials: Students will need to have access to computers.

Procedure:

1. Assign each group a topic from the list below (or your own additional topics):

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The Dead Zone in the Gulf of MexicoLake Nyos in AfricaFlouride in Drinking WaterThe Dead Zone in Lake ErieMercury in the Amazon RiverAcid Rain and dead lakes

2. Students will conduct research using databases and good internet sites. They shouldinclude maps, charts, graphs and illustrations.

3. The PowerPoint presentation should include the following informationWhat is the environmental issue?

What is the primary chemical element that is causing the problem?Describe that element.

Does this element have always positive or always negative effects on livingorganisms? What does the effect depend on?

For your specific environmental issue, what are the sources of the chemicalelement?

What factors should be considered when addressing this issue?

Should this issue be a concern to us? What do you think should be done?

4. Students will present to the rest of the class with follow up discussion and questions.

Additional Resources

Text and various diagrams to describe four biogeochemical cycles that operate innature.http://www.marietta.edu/~biol/102/ecosystem.html#BioGeoChemicalCycles8

Plans for a game to learn about the carbon cyclehttp://gk12.asu.edu/curriculum/life_science/CarbonAdventures/carb_ad.htm

Another lesson for introducing the carbon cyclehttp://www.ucar.edu/learn/1_4_2_15t.htm

E2.3

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Carbon cycle and Global warming –good data tables and graphs, lesson uses higherlevel reflection and analysiswww.kbs.msu.edu/k12/resources/documents/GlobalClimateChange-LessonPlan.doc

Nitrogen cycle, human impacts and water testinghttp://extension.usu.edu/files/publications/publication/pub__3588118.pdf

Lesson plan using bottle biology to study ecosystems with a special emphasis onnutrient cycling and energy flows. Uses Vernier probes and digital camerahttp://techplan.edzone.net/ci2006/BottleBiology.doc***For a similar activity without the probes:http://www.uen.org/Lessonplan/preview.cgi?LPid=1797

Interactive website on the Gulf of Mexico dead zone:http://www.smm.org/deadzone/top.html