Energy Flow in Ecosystems
Background: Ecologists represent energy budgets/flow in ecosystems, for instance, with the familiar box and arrow diagrams and energy pyramids seen in all textbooks. The many complex concepts and thinking (FRAMEWORK) embodied in these representations include: "energy" exists in different forms (sunlight, chemical bonds, reserves within organisms) and is therefore transformed within ecosystems; energy is degraded during these transformation?s and lost from the ecosystem (but conserved); although energy and matter are different entities, at the atomic scale chemical energy is due to associations (electronic forces) of atoms in molecules; energy release and uptake necessarily involve transformations of matter (carbon) from one form to another. Faculty assume students understand these quite sophisticated ideas and others below, but research shows that they often do not. This is the hidden curriculum?.
HIDDEN CURRICULUM • Principled Thinking? Addressed
- Principles? - Conservation of Energy? (the biosphere is open with respect to energy - sunlight is the ultimate source of energy in the biosphere); energy and matter are related (energy can cycle through ecosystems in conjunction with matter as chemical bond energy; energy and matter are not interchangeable).
- Processes? Generation? (photosynthesis); Transformation (building of biomolecules within an organism, consumption of one organism by another); Oxidation? (autotrophic respiration, heterotrophic respiration, decomposition)
- Scale & Time: Students - comprehend the molecular and cellular processes that take place in photosynthesis and cellular respiration; where these occur within organisms such as plants, bacteria and animals; and how these molecular/cellular/organismal processes collectively contribute to ecosystem processes.
- Forms & Representations: Ecosystems Matter & Energy Flow (Students can interpret Energy pyramids; Box-and-arrow diagrams, including what they are and the principles they illustrate; recognize that glucose (and other organic) molecules are a form of potential chemical energy; recognize the different forms energy can assume in ecosystems.
USING THE DQCs: 4 STEPS
The following 4 steps bring you through the process of selecting and using Diagnostic Question Clusters, interpreting student responses so you can focus on the concepts and thinking students appear to find most challenging, using active-teaching methods to help students make progress on these challenges, and finally gauging student improvement.
2. Administer DQC and make a Diagnosis. First give students the Diagnostic Questions you chose (e.g. in class, as homework - see DQC pages). Then look at their responses and try to figure out what these responses mean (diagnosis). In other words, identify students' unprincipled thinking concerning Energy & Ecosystems. See diagnostic interpretations for Energy Pyramid and Rainforest DQC's.
3. Use student active approaches to help students improve their understanding of the concepts and principled thinking. Once you figure out what your students need help with, you can use a variety of student-active approaches in class/as homework that should help them make progress. Below is a list of outcomes concerning Energy & Ecosystems and associated active teaching approaches. These are examples you can use and modify as you wish.
Outcome: Students Better Understand
Active Teaching Approach
1. That energy flow is unidirectional; energy loss in trophic transfer
2. Energy loss between trophic levels
3. Cellular respiration: atomic/molecular and organismal scales
4. Cellular respiration results in heat loss