Photosynthesis

This model places students inside a chloroplast where light reactions in the thylakoid stacks and the Calvin cycle in the stroma turn light, carbon dioxide and water into sugar and oxygen. Two sliders set light intensity and CO2 concentration, and the rate follows whichever input is scarcer, so the readout names the limiting factor. Counters tally molecules used and made, settling at the 6 : 6 : 1 : 6 ratio of the equation. It works well for teaching limiting factors, reading rate graphs and linking the balanced equation to what actually happens.

• Set Light intensity to 200 and raise it step by step until Sugar made stops rising.
• Keep light high and drag CO2 concentration down to 100 ppm to see the limiting factor switch.
• Read the Limiting factor readout each time you change a slider and explain why it changed.
• Watch the Used and Made counters and compare the ratio with 6CO2 + 6H2O to C6H12O6 + 6O2.
• Set light to 0 and observe that the rate falls to zero even when CO2 is plentiful.

1. 1Write and interpret the balanced equation for photosynthesis.
2. 2Identify light and carbon dioxide as factors that can limit the rate.
3. 3Explain why raising one factor stops helping once another becomes scarce.
4. 4Describe where the light reactions and the Calvin cycle take place in a chloroplast.

Questions teachers ask