5th Grade Science Unit 7

Vermilion Parish Schools "Connecting Students, Home and Schools"

Activity 5: Nature’s Cycles In Action: The Carbon Cycle and the Nitrogen Cycle (SI GLEs: 3, 4, 5, 20, 21, 22, 40; SE GLEs: 49, 50, 51)

Materials List: Internet access, diagrams of nitrogen and carbon cycles, poster board, markers,  soil, water, decomposing plant matter, sterilized manure, disposable gloves, legumes, topsoil, fertilizer, soil and/or water test kit, containers for soil and/or water

Be sure that students discuss safety concerns about working with soil, manure, decomposing plant material, soil and water testing chemicals, etc. before beginning the first activity and determine proper safety procedures to follow to conduct the experiment.

To further investigate the carbon cycle and the nitrogen cycle, have students perform the following:

Part A: Carbon Cycle—(1-2 class periods)

Provide students with a diagram of the carbon cycle, such as the one found at the following website: Carbon: the Element of Surprise or an animated diagram, such as the one that can be found at the following website: EPA Climate Change Kids Page: The Carbon Cycle Movie,. Students should view the movie to learn about the carbon sinks on land, in the air, and in water. Students should use the diagrams to determine where the carbon sinks on Earth can be found. (A carbon sink is a place on Earth where carbon is stored in large quantities.) List the places on the board; then ask students to explain how each sink was created. Students may draw on material previously read at the beginning of the activity to form their explanations or use information found at one of the new websites.  Instruct pairs of students to choose one carbon sink to research further. They should find out how it was formed, how carbon cycles through it and how fast it cycles. Student pairs should identify key vocabulary words for their carbon sink and use the vocabulary card strategy (view literacy strategy descriptions) to create vocabulary cards (refer to Unit 4, Activity 3 for an example of a card). Students should create cards for words such as slow-track carbon recycling, fast-track carbon recycling, carbon sink, atmosphere, fossil fuel, deforestation, transpiration, respiration, etc. Using the word “carbon sink,” for example, students would write the word in the middle of the card. In the left top corner of the card, students would write the definition of a carbon sink (an area which traps and stores carbon). On the top right of the card, students should describe characteristics of a carbon sink (contains a large amount of carbon in the form of carbon dioxide or elemental carbon). On the bottom left of the card, students can write examples of carbon sinks (oceans, forests, and the atmosphere). Finally, on the bottom right of the card, students can draw an illustration of a carbon sink (an ocean, forest, or the atmosphere). 

Explain to students that carbon cycles through each sink and moves from one sink into another as part of the carbon cycle. Students should draw their carbon sink and share it with the rest of the class. Their sink should be the main emphasis in the drawing; however, it may be necessary to include one or more aspect of another sink to show how carbon enters a carbon sink or how it is released from it. (For example, when illustrating the atmosphere, students may need to include a drawing of how carbon from a factory is being released into the air, in addition to showing molecules of CO2 floating in the atmosphere, along with oxygen molecules, nitrogen molecules, and other atmospheric components.)  Have students explain how long carbon remains in each sink and identify if it is an example of fast track carbon cycling or slow track carbon cycling. Students should use the vocabulary words identified for their carbon sink in their explanation.  Hang all drawings on the wall in front of the class. Once all students have shared their carbon sinks, have students use large poster board arrows to make connections between each other’s sinks to illustrate how carbon cycles through different sinks. Vocabulary cards can be attached to the diagram to help other students understand the terms. Be sure that students identify whether each cycling process is a slow track or fast track cycle.

Additional information on the carbon cycle can be obtained from the video, Carbon: Element of Surprise, available through Louisiana Public Broadcasting’s Instructional Television broadcast (viewing and taping dates can be found at video streaming from United Streaming, provided by LPB. Accompanying lessons can be found. (EnviroTackleBox)

Part B: Nitrogen Cycle (1 class period)

Students should review a diagram showing the nitrogen cycle and discuss how nitrogen moves through the atmosphere into the soil, how bacteria fix nitrogen for plant use, how plants utilize nitrogen, and how it is released back into the atmosphere and soil. Ask students to list different natural materials that provide nitrogen to the soil and water. Elicit from students sources from which nitrogen can be obtained, including decomposing plant material, animal waste, legumes, and fertilizers (man-made). Guide students to design an experiment that would help them determine which source provides the most nitrogen to the soil or water. Students could set up containers of equal amounts of soil or water and then use equal amounts of the nitrogen sources. If an actual experiment is performed, starting and ending levels of nitrogen in the soil or water should be determined using a soil or water testing kit that tests for nitrogen.  Students should identify independent and dependent variables and controls needed to perform a viable experiment. Students need to write the steps that should be followed to test their hypothesis correctly. Students should perform the experiment, record results, and discuss outcomes. This activity will take at least two weeks to determine the outcomes. Ask students

  • How have scientists used knowledge about the nitrogen cycle to improve crop production? (Understanding the chemistry of nitrogen in soils and how nitrogen is “fixed” for plant use can help farmers supply sufficient nitrogen for crop needs.)

  • Which method of increasing nitrogen was most effective in the shortest amount of time? What observations were used to determine which soil or water sample had the greatest increase in nitrogen? (Measurements of increases in nitrogen were observations.) How can these results be used to help farmers improve crop production? Explain.

  • What evidence in the water samples indicates an increase in nitrogen? (increases in algae growth) Students should understand that they are making an inference about increased nitrogen from the increase in algae. Actual measurements of the nitrogen levels are quantifiable observations.

  • What effect does excess nitrogen have on algae growth in waterways? How have scientists used this knowledge to decrease pollution in waterways?  (Excess nitrogen increases algae growth in waterways, causing depleted oxygen supply for organisms with gills when the algae die and decompose. Increased algae blooms cloud the water and cause temperature increases which allow less oxygen to remain dissolved in water and decrease water quality. Scientists have created best management practices to be used to control excess nitrogen from entering water bodies.)

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