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McREL Standards Activity


Chemical Cycles


Purpose:As a result of this activity, students will be able to identify different ways that chemical elements are recombined as they are transferred among living and nonliving components of ecosystems.
Related Standard & Benchmarks:
Science
 Standard 6.Understands relationships among organisms and their physical environment
   Level IV [Grade 9-12]
   Benchmark 3. Knows that as matter and energy flow through different levels of organization in living systems and between living systems and the physical environment, chemical elements (e.g., carbon, nitrogen) are recombined in different ways
Science
 Standard 2.Understands Earth's composition and structure
   Level IV [Grade 9-12]
   Benchmark 3. Knows that elements exist in fixed amounts and move through the solid Earth, oceans, atmosphere, and living things as part of geochemical cycles (e.g., carbon cycle, nitrogen cycle)
Student Product:Diagram and discussion
Material & Resources:Materials for diagrams (e.g., paper, markers)
Teacher's Note:This activity is intended to follow a lesson on biogeochemical cycles; it provides the opportunity for students to relate what they’ve learned to a specific, real-world setting.
Activity
Provide students with pictures or posters of various ecosystems that students may be familiar with (e.g., forest, prairie, desert, alpine, wetland, ocean, river, urban area). Students should create a diagram in the manner of a flow chart that traces a possible path (or paths) of a specific atom (e.g., carbon, nitrogen) in an ecosystem; they should focus on the different forms the atom takes as it recombines with other elements. Encourage students to be specific in their diagram; they should consider the specific roles of various organisms (including animals, fungi, plants and algae, protozoa, and bacteria), biological processes (e.g., photosynthesis, respiration, digestion, decomposition), and physical processes (e.g., erosion, combustion, chemical interactions) in biogeochemical cycling. [For example, a carbon atom is present in organic matter in a forest; a forest fire releases the carbon atom into the air as carbon dioxide; the carbon dioxide is taken up by a plant leaf and converted to a sugar molecule via photosynthesis; the sugar is then converted to a starch molecule in the root; an animal eats the root and an intestinal bacterium breaks down the sugar, releasing carbon dioxide or methane as a respiration product; the carbon molecule then continues in another cycle.] Discuss similarities and differences among the students’ diagrams, emphasizing the shared processes. Further discussion might focus on the links between ecosystems, as well as the cycling of pollutants such as petroluem products or heavy metals (e.g., lead, mercury).