Directions 1. Use the instructional model to show students where they are in the course of the unit. Show Slide 2 of the Fluxes Change and Photosynthesis Limits PPT. 2. Review the Constant Fluxes Model and introduce the Changing Fluxes Model. Show Slide 3. Pass out the 4.3 Computer Model for Changing Fluxes Handout to each student. In partners or as a whole class, have students read the handout. Discuss how the Constant Flux and Changing Fluxes Models are different. Review the idea of carrying capacity for Activity 2.4 and relate it to the photosynthesis flux. 3. Show students how to use the simulation. Show Slide 4 and open the simulation. Show students how to move the sliders and run an example. Point out the graphs and how they can slide the line of the graph to get data for a particular point in time. 4. Students run the simulation. Pass out the 4.3 Computer Model for Changing Fluxes Worksheet to each student. Have students follow the instructions to run the simulation. Students should record their data in the tables. (Optional) Use Slides 5-13 to discuss Run 1, 2, and 3 as a class. Students can complete the tables on Slides 5, 8, and 11 on their worksheets. Results from example runs are shown in both graph and table form. 5. Students consider patterns in their results. When students have completed the tables, have students work individually and then with a partner to answer the questions in Part B on 4.3 Computer Model for Changing Fluxes Worksheet . 6. Discuss the patterns. Show Slide 14. Have students share and discuss their answers to questions. 7. Have students complete an exit ticket Show slide 15 of the 4.3 How Fluxes Change and Photosynthesis Limits PPT. Conclusions: Why do ecosystems with unbalanced fluxes often stabilize? Predictions: What can cause stable ecosystems to become unstable? On a sheet of paper or a sticky note, have students individually answer the exit ticket questions. Depending on time, you may have students answer both questions, assign students to answer a particular question, or let students choose one question to answer. Collect and review the answers. The conclusions question will provide you with information about what your students are taking away from the activity. Student answers to the conclusions question can be used on the Driving Questions Board (if you are using one). The predictions question allows students to begin thinking about the next activity and allows you to assess their current ideas as you prepare for the next activity. Student answers to the predictions question can be used as a lead into the next activity.