Ecosystems Lesson 1 Background Information

Three-dimensional Learning Progression

In previous Carbon TIME units, students learned to explain macroscopic processes (plant growth, combustion, decay, etc.) in terms of atomic molecular processes. In this unit, they must connect the macroscopic and atomic molecular scales to matter cycling and energy flow at the larger ecosystem scale. Here are some questions to think about as you read your students’ pretest responses and listen to their ideas:

  • Are they distinguishing between individual plants and animals and populations or trophic levels? Students will need to learn that food chains and food webs tell about relationships between populations and flows of matter and energy, not just “who eats who.”
  • Are they distinguishing matter from energy? Matter and energy move together through food chains and food webs, so students can confuse organic matter with the chemical energy in organic matter and still answer a lot of questions correctly, but matter and energy “go their separate ways” at the beginning and end of food chains and food webs:
    • Producers get matter ONLY from CO2, water, and minerals, and energy ONLY from sunlight.
    • When organisms use organic matter for cellular respiration, ALL the matter goes back into CO2, water, and minerals, while ALL the energy leaves the ecosystem as heat (which is ultimately radiated out into space). So, matter cycles and energy flows through ecosystems.
  • Are they connecting scales? Students will need to apply what they learned about transformations of matter and energy in individual organisms to ecosystem-scale processes—to see how matter cycling and energy flow in ecosystems result from the atomic-molecular processes of photosynthesis, biosynthesis, digestion, and cellular respiration. Many students find this a hard connection to make. This lesson will help students begin thinking about these ideas and will give you a chance to see where your students are starting.