SE4 Identify cycles, change, and stability in ecosystems

Suggested time: 3-5 hours

Learning Objectives

1. illustrate the cycling of nutrients and matter through biotic and abiotic components of an ecosystem by tracking carbon, nitrogen, and oxygen.
   
2. Select and use appropriate vocabulary and modes of representation to communicate scientific ideas. (COM)
   
3. Identify and respect various cultural perspectives on the cycling of nutrients and matter through the environment. (CCT)
   
4. State a prediction and a hypothesis based on available evidence and background information.
   

Enrichment Learning Objectives

1. illustrate the cycling of nutrients and matter through biotic and abiotic components of an ecosystem by tracking phosphorus.
   

Key Questions

1. How does the concept of cycles help humans understand the workings of a complex entity such as an ecosystem?
   
2. How do various cultures explain and value environmental interactions using concepts of cycles and equilibrium?
   
3. How do carbon, nitrogen, and oxygen cycle through an ecosystem?
   
4. How do human actions affect nutrient cycles in an ecosystem?
   

Key Concepts

• A nutrient is any substance needed by an organism for proper growth, repair, and function such as nitrogen, oxygen, carbon, water, phosphorus, sulphur, hydrogen.
• A biogeochemical cycle or nutrient cycle is the path of a nutrient through an ecosystem.
• Cellular respiration is the process by which most living things generate useful energy by combining oxygen and sugars to produce carbon dioxide and water.
• Photosynthesis is the process by which green plants and other producers use energy from the sun, and carbon dioxide and water to produce sugars and oxygen.
• Nitrogen fixation is the conversion of atmospheric nitrogen gas into compounds that are usable by plants, typically nitrate ions or ammonia.
  

Pre-Instructional Questions

1. Are students able to identify biotic and abiotic factors within an ecosystem?
   
2. Do students understand what a nutrient is?
   
3. Do students understand the processes of cellular respiration and photosynthesis?
   

Suggested Teaching Strategies and Activities

1. Students should create visual representations identifying biotic and abiotic pathways through which carbon, nitrogen, and oxygen cycle through a specific terrestrial or aquatic ecosystem. Representations could identify each cycle separately or show a combination of two or all three of the cycles. Students should discuss how their representations represent simplified versions of reality given that there is considerable overlap in the nutrient cycles. Scientists often choose to study complex systems by reducing them to simpler, more understandable entities. Students should discuss the benefits and drawbacks to this approach.
   
   
2. Students should explain how the components of each nutrient cycle support the stability of the ecosystem. Student explanations should identify the key processes of each cycle, where each process occurs in the cycle, and which biotic or abiotic factors are involved in each process. Students should consider the impact of changes to one or more aspects of each nutrient cycle by considering questions such as: What happens to the bodies of dead organisms? What would happen if nutrients (or one nutrient) quit cycling? What would happen if animals produced a substance other than carbon dioxide during respiration?
   
   
3. Students could investigate one or more aspects of the carbon cycle. For example, students might demonstrate that plants absorb carbon dioxide, an activity that could be integrated with the study of acids and bases in the Chemical Reactions unit. Alternatively, students might conduct an experiment to determine the effects of different carbon dioxide levels on plant growth.
   
   
4. Students should provide explanations of the processes of photosynthesis and cellular respiration, and explain how these processes relate to the carbon and oxygen cycles. Student explanations should identify which organisms at each trophic level in a specific ecosystem carry out photosynthesis and cellular respiration. This activity could be integrated with the Chemical Reactions unit by having students write balanced chemical equations for the processes of photosynthesis and cellular respiration, and identifying the sources of the reactants and how organisms use the products. A common misconception is that plants do not use O₂ or carry out cellular respiration but the reality is that they do; they just happen to produce more O₂ than they use.
   
   
5. Students could conduct an experiment to investigate one or more aspects of the nitrogen cycle. For example, students might determine how varying the role or type of fertilizers affects plant growth.
   
   
6. Students could create a closed system (e.g., terrarium, aquarium) containing biotic and abiotic components and identify the nutrient cycles in that system and relate them to the Earth's nutrient cycles.
   
   
7. Students could compare scientific perspectives of the cyclical nature of matter and the interconnectedness of the biotic and abiotic factors in an ecosystem with Indigenous or other cultural worldviews. Such a comparison helps to validate multiple perspectives or worldviews, and helps students understand how their personal beliefs may contradict scientific perspectives.