Biogeochemical Cycles

Transcription

1 Darlene Roche Clarkston Schools Biogeochemical Cycles Content Statement: E2.3 The Earth is a system containing essentially a fixed amount of each stable chemical atom or element. Most elements can exist in several different states and chemical forms; they move within and between the geosphere, atmosphere, hydrosphere, and biosphere as part of the Earth system. The movements can be slow or rapid. Elements and compounds have significant impacts on the biosphere and have important impacts on human 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 Earth System and how those forms can be beneficial or harmful to humans. E2.3b Explain why small amounts of some chemical forms may be beneficial for life 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 the geosphere) 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 how does their movement effect living things? Background Information: CARBON CYCLE Carbon 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, carbon dioxide 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 eat them. 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

2 carbon into the ground. Some becomes buried miles underground and will become fossil fuels in millions and millions of years. Carbon moves from living things to the atmosphere. Each time you exhale, you are releasing carbon dioxide gas (CO2) into the atmosphere. Animals and plants get rid of carbon dioxide gas through a process called respiration. Carbon moves from fossil fuels to the atmosphere when fuels are burned. When humans burn fossil fuels to power factories, power plants, cars and trucks, most of the carbon quickly enters the atmosphere as carbon dioxide gas. Each year, five and a half billion tons of carbon is released by burning fossil fuels. That s the weight of 100 million adult African elephants! Of the huge amount of carbon that is released from fuels, 3.3 billion tons enters the atmosphere and most of the rest becomes dissolved in seawater. 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 and other greenhouse gases, Earth would be a frozen world. But humans have burned so much fuel that there is about 30% more carbon dioxide in the air today than there was about 150 years ago. The atmosphere has not held this much carbon for at least 420,000 years according to data from ice cores. More greenhouse gasses such as carbon dioxide in our atmosphere are causing our planet to become warmer. Carbon moves through our planet over longer time scales as well. For example, over millions of years weathering of rocks on land may add carbon to surface water which eventually 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, over long time scales, carbon is removed from seawater when the shells and bones of marine animals and plankton collect on the sea floor. These shells and bones are made of limestone, which contains carbon. When they are deposited on the sea floor, carbon is stored from the rest of the carbon cycle for some amount of time. The amount of 2

3 limestone deposited in the ocean depends somewhat on the amount of warm, tropical, shallow oceans on the planet because this is where prolific limestone-producing organisms such as corals live. The carbon can be released back to the atmosphere if the limestone melts or is metamorphosed in a subduction zone Windows to the Universe, at at the University Corporation for Atmospheric Research (UCAR) , 2000 NITROGEN CYCLE Nitrogen 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 biogeochemical cycles and is very important for ecosystems. Nitrogen moves slowly through the cycle and is stored in reservoirs such as the atmosphere, living organisms, soils, and oceans along its way. Most of the nitrogen on Earth is in the atmosphere. Approximately 80% of the molecules in Earth s atmosphere are made of two nitrogen atoms bonded together (N2). All plants and animals need nitrogen to make amino acids, proteins and DNA, but the nitrogen in the atmosphere is not in a form that they can use. The molecules of nitrogen in the atmosphere can become usable for living things when they are broken apart during lightning strikes or fires, by certain types of bacteria, or by bacteria associated with legume plants. Other plants get the nitrogen they need from the soils or water in which they live mostly in the form of inorganic nitrate (NO3-). Nitrogen is a limiting factor for plant growth. Animals get the nitrogen they need by consuming plants or other animals that contain organic molecules composed partially of nitrogen. When organisms die, their bodies decompose bringing the 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 process called mineralization. The ammonium salts are absorbed onto clay in the soil and then chemically altered by bacteria into nitrite (NO2- ) and then nitrate (NO3- ). Nitrate is the form commonly used by plants. It is easily dissolved in water and leached from the soil 3

4 system. Dissolved nitrate can be returned to the atmosphere by certain bacteria in a process called denitrification. Certain actions of humans are causing changes to the nitrogen cycle and the amount of nitrogen that is stored in reservoirs. The use of nitrogen-rich fertilizers can cause nutrient leaching in nearby waterways as nitrates from the fertilizer wash into streams and ponds. The increased nitrate levels cause plants to grow rapidly until they use up the nitrate supply and die. The number of herbivores will increase when the plant supply increases and then the herbivores are left without a food source when the plants die. 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 releases various solid forms of nitrogen. Farming also affects the nitrogen cycle. The waste associated 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." University Corporation for Atmospheric Research. 20 Jun 2007 at Windows to the Universe: The Nitrogen Cycle 4

5 ACTIVITY 1: Introducing the Global Carbon Cycle Adapted from Utah State Office of Education, Curriculum Section, Salt Lake City, Utah, Summary: This activity could be used to introduce the carbon cycle. It is an inquiry lesson 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 location Flux- a change Teaching and Learning Strategies: Ensure inquiry: Students will develop independent group charts illustrating the carbon cycle. Teachers should not feel the need to answer all their questions, let the students discover their own answers. Teachers can use student feedback to assess prior knowledge and misconceptions. When helping students, teachers can stimulate the thought process by answering student questions with questions. Problem: Speculate on possible pathways a carbon atom might follow over a short and long 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 materials listed. 2. Students should label each card with a possible reservoir where they think a large amount of carbon would be found in the Earth system. 3. After index cards are labeled and filled in, have students decide which of the reservoirs represents the largest and smallest reservoir of carbon atoms on a global 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 the cards 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 5

6 and writing down the process that moved the carbon atom. Students should now draw in their arrows and label the arrows indicating the process that the carbon atom might have to go through in order to move from one of their reservoirs to the other. 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 charts rather than just differences. Important answers to include are as follows: Table 1: Some carbon-containing substances and their global locations Common carbon-containing substances carbon dioxide carbon dioxide (dissolved) plants animals Rocks/minerals/soil Fossil fuels Major Global Locations atmosphere hydrosphere biosphere biosphere geosphere geosphere 7. Use these similar answers to begin to create a large flow diagram on the board or overhead projector. 8. Now, have the class identify and discuss different carbon fluxes and add those arrows and processes to the diagram on the board. Some likely examples include: fossil fuels (burning) atmosphere atmosphere (photosynthesis) plants plants & animals (respiration) atmosphere land- (acid rain attack on carbonates)- atmosphere dead plants & animals (decomposition) soil atmosphere (dissolving) ocean 6

7 plants (digestion) animals animals (create waste) soil decomposed 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 of carbon. 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 to create the diagram) REINFORCEMENT: Students who require extra review can go to the following website to play the Carbon Cycle Game. 7

8 ACTIVITY 2: Carbon Sources and Sinks Lab Adapted from "Climate Discovery Teacher's Guide." University Corporation for Atmospheric Research. 20 Jun 2007 at Summary: Students will use a chemical indicator (Bromothymol blue) to detect the presence of carbon dioxide and investigate ways that carbon dioxide moves into and out of 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 min Teaching: 40 min Discussion: 30 min Materials for Teacher Balloon filled with automobile exhaust (see Advanced Preparation) Beaker Bromothymol blue (BTB) Cotton ball Straw Materials for Student Teams: Test tube rack Six test tubes One hole stopper with tubing attached Vinegar Bottle of BTB working solution Sprig of Elodea (available in pet stores) Marker Masking tape Aluminum foil Baking soda Cotton balls Straws 8

9 Safety goggles for protection in case of splash or glass breakage 9

10 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 automobile exhaust 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 students the day before. Directions for the set-up are in the Part 3 section on the following page. 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 balloons with 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 make them easier to fill with the relatively low-pressure exhaust. 3. Prepare a cone to collect the car exhaust by rolling up a manila folder lengthwise. One end must be larger than the opening for the car s tail pipe and the 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 cone fairly airtight. Note: the paper funnel will work for several fillings without burning. DO NOT use a plastic funnel. As the exhaust pipe heats up, the plastic may melt. You may use a metal funnel, but be VERY careful to avoid any skin contact 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 seal between the cone and the exhaust pipe. DO NOT BREATHE THE EXHAUST. The balloon should fill quickly; if not, have your assistant step lightly on the accelerator. 8. When the balloon is filled, have an assistant use a twist tie or two to tightly seal the balloon. Do this by twisting the neck several times and doubling it over once, 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 to prepare a few extra filled balloons. Background Information Carbon 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, called carbonic acid. The chemical bromothymol blue (BTB) is a sensitive indicator of the presence of acid. When gas containing CO2 is bubbled through a BTB solution, carbonic acid forms and the indicator turns from dark blue to green, yellow, or very pale yellow depending on the CO2 concentration (lighter colors mean higher concentrations). 10

11 Carbon dioxide (CO2) provides the bubble in your soda pop and the rise in your baked goods. But it is also a very significant greenhouse gas. CO2 is important in maintaining the earth s average temperature of about 15 C (59 F). The CO2 traps infrared energy emitted from the earth s surface and warms the atmosphere. Without water vapor, CO2, and methane (the three most important naturally produced greenhouse gases), the earth s surface would be about -18 C (0 F). At this temperature, it is doubtful that complex life as we know it would ever have evolved. 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 (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, providing evidence 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 BTB 2. 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 and pinch 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 of the balloon up to the twisted portion. Seal the opening of the balloon tightly to one side by pinching it off with fingers. (You may need to practice this a few times 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 and Conclusion questions. Extension: Ask students to devise their own experiment to test other sources and sinks of carbon dioxide (e.g. carbonated beverages, lime based chalk) 11

12 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 baked goods. But it is also a very significant greenhouse gas. CO2 is important in maintaining the earth s average temperature of about 15 C (59 F). The CO2 traps infrared energy emitted from the earth s surface and warms the atmosphere. Currently, the amount of carbon dioxide and other greenhouses gasses in the atmosphere is increasing causing global warming. In this activity you will discover some of the ways that carbon dioxide gets into and out of the atmosphere. What you ll need: Six test tubes and a rack One hole stopper with tubing attached Baking soda Vinegar Aluminum foil Safety goggles Cotton balls Straws Bottle of BTB working solution Sprig of Elodea (a water plant) Masking tape and a marker Part 1: Detecting CO2 Gas 1. 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 the BTB solution. (Tube A will be the control, tube B will be the treatment.) Place the 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 the stopper and tubing. 5. Place the free end of the tubing into tube B. Make sure that the end of the tubing 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 sideto-side. Don t shake it upside down! Gas bubbles will begin to bubble rapidly out 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? 12

13 Part 2: Are animals a source of CO2? 1. Fill a test tube C approximately 1/3 full of BTB 2. 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 BTB 2. 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? 13

14 ANALYSIS & CONCLUSIONS: 1. After finishing all five parts of this activity, compare the colors in all the tubes. 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, which source would be most important to control? Explain why. 4. Would there be problems with such controls? If so, what might they be? 14

15 ACTIVITY 3: Introducing the Nitrogen Cycle Climate Discovery Teacher's Guide." University Corporation for Atmospheric Research. 20 Jun 2007 at Traveling Nitrogen Learning Goals Students will Learn that nitrogen cycles indefinitely through the Earth system and will understand 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 Lesson Students play the role of nitrogen atoms traveling through the nitrogen cycle to gain understanding of the varied pathways through the cycle and the relevance of nitrogen to living 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 min Teaching: 30 min Assessment: 20 min Materials for Class 11 Dice Dice Codes (see website or printed materials) Signs with station names (see Advanced Preparation) 11 small rubber stamps 11 ink pads Materials for Students: Passport Student Page (see website or printed materials) Pen or pencil Lined paper 15

16 Advanced Preparation **If you do not have the printed materials for this content expectation, the Dice Codes and Passport Student Page can be found at the following website: 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, plants and animals and that the class is going to discover how nitrogen travels. You may want to have students read the Windows to the Universe page entitled The Nitrogen Cycle either prior to or following the lesson 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 stations around the room) based on rolling dice. Tell students that they will each carry a nitrogen passport with them and stamp it each time they get to a nitrogen reservoir station. Then toss the die at the reservoir to find out what your next destination will be. Write a note in the passport to indicate how you are getting 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 to start traveling with their Passport Student Page by rolling the die at their stations. 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. Assessment Have students write a paragraph about their trip through the nitrogen cycle. Include information about (1) where they went, and (2) how they got to each destination. 16

17 ACTIVITY 4: Nitrogen Fixation Investigation Adapted from Errington, Barbara. "Nitrogen Fixation, OR What a Gas!." Access Excellence Activities Exchange The National Health Museum. 20 Jun Summary: This is a long term project designed to illustrate nitrogen fixation and the symbiotic relationship of organisms. Students gain skill in the design, implementation and reporting of a scientific research project using the scientific method. Specifically, students will set up an experiment to determine what effect adding Rhizobium bacteria to legume 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 symbiotic relationship with legumes--these types of plants are very useful because the nitrogen fixation enriches the soil and acts as a 'natural' fertilizer. The nitrogen-fixing bacteria form nitrates out of the atmospheric nitrogen which can be taken up and dissolved in soil water by the roots of plants. Then, the nitrates are incorporated by the plants to form proteins, which can then be spread through the food chain. When organisms excrete wastes, nitrogen is released into the environment. Also, whenever an organism dies, decomposers break down the corpse into nitrogen in the form of ammonia. This nitrogen can 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-up 6-8 weeks for plant growth One 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 pots 3. Vermiculite, enough to fill the pots 4. 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 from any biological supply house.) 6. Plastic wrap 7. Nitrogen-free nutrients (see teacher instructions) 8. Distilled water 17

18 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 critical for plants and animals, but is found mainly in the atmosphere in a form that they cannot use. You may want to model the strong triple covalent bond that makes an N2 molecule so difficult to break apart. Try using 3 identical springs and showing the difference in strength it takes to pull on the opposite ends of one spring, two springs and then 3 springs. (You may need to dramatize the efforts needed, depending on the elastic strength of your springs.). Follow up with a discussion about 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 or pets, but will cause legume roots to form nodules. Tell the students: "The purpose of our investigation will be to find out what effect bacterial interactions have on plants of the bean family." 4. Ask students: "How can we see if a plant is affected by the nodules?" Answers will vary, but get to factors such as height and weight of a plant as it grows compared 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 plant growth. 6. After lab setup, students are to state their hypothesis, procedures, data table, etc. Post-lab 1. Place average data from each lab team on board and determine overall class results. Discuss significant deviations, review scientific error, use of larger sample size, 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. Have students observe under the microscope. Directions for Nitrogen-free nutrients 0.2g dihydrogen phosphate 0.8g potassium monohydrogen phosphate 0.2g magnesium sulfate 0.1g calcium sulfate 0.01g ferric sulfate Combine the above minerals and store in a covered container. Instruct students to add 1.3 grams to one liter of distilled water. 18

19 Background: Student Instructions Nitrogen Fixation, OR What a Gas! The environment of plant roots is composed of many types of organisms including bacteria, fungi, and invertebrates. To survive, plants have evolved ways to interact with these organisms ranging from defense mechanisms against pathogens to symbiotic relationships that are mutually beneficial. Objectives: To describe and explain the importance of nitrogen fixation To investigate the symbiotic relationship between bacteria and plant roots To gain skill in using the scientific method Problem: What is the effect of nitrogen fixation via a symbiotic relationship with bacteria on the length and weight of a selected legume plant? Materials and Equipment: 1. Two 12.5 cm plastic pots 2. Vermiculite, enough to fill the pots 3. Six legume seeds 4. CommercialRhizobium 5. Nitrogen-free nutrients 6. Masking tape or permanent marker for labeling pots 7. 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 pot 5. 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 19

20 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 equal the 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 situations that are created by an imbalance of chemical elements within the Earth System. Each group 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): 20

21 The Dead Zone in the Gulf of Mexico Lake Nyos in Africa Flouride in Drinking Water The Dead Zone in Lake Erie Mercury in the Amazon River Acid Rain and dead lakes 2. Students will conduct research using databases and good internet sites. They should include maps, charts, graphs and illustrations. 3. The PowerPoint presentation should include the following information What 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 living organisms? What does the effect depend on? For your specific environmental issue, what are the sources of the chemical element? 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 in nature. Plans for a game to learn about the carbon cycle Another lesson for introducing the carbon cycle 21

22 Carbon cycle and Global warming good data tables and graphs, lesson uses higher level reflection and analysis Nitrogen cycle, human impacts and water testing pdf Lesson plan using bottle biology to study ecosystems with a special emphasis on nutrient cycling and energy flows. Uses Vernier probes and digital camera ***For a similar activity without the probes: Interactive website on the Gulf of Mexico dead zone: 22