C3, C4 and CAM Photosynthesis and Photorespiration
BiologyPlant PhysiologyAges 16–17
Use it with your class: students open it from a link or a QR code, with no account needed.
Next in Plant Physiology
Compare the net photosynthesis of wheat (C3) and maize (C4) as you change light, CO₂ and temperature, and watch photorespiration rise in hot air or at low CO₂. Look inside the leaf at Kranz anatomy and the Hatch–Slack steps, count Rubisco reactions with CO₂ and O₂, then run a day of a pineapple (CAM) that opens its stomata at night.
Lesson: Photosynthesis in C3, C4 and CAM plants; photorespiration
What it shows
Rubisco, the enzyme that fixes CO₂ in the Calvin cycle, can also react with O₂. The plant then loses part of the carbon it has fixed: this is photorespiration, and it rises in hot weather and when CO₂ around the enzyme is low. C4 plants such as maize first fix CO₂ with PEP carboxylase in mesophyll cells and release it around Rubisco in bundle-sheath cells, so they hardly photorespire. CAM plants such as pineapple open their stomata at night and store CO₂ as malic acid, which saves water. The numbers come from a teaching model, not from measurements of one variety.
How to use
On Compare C3 and C4, drag Light, CO₂ and Temperature, choose the graph's x-axis and press Record. On Inside the leaf, choose the Maize (C4) or Wheat (C3) leaf, follow the steps and press Count 200 reactions. On CAM plant, set the day and night temperatures and press Run one day.
Parameters you can change
- Screen Compare C3 and C4, Inside the leaf, CAM plant
- Light (share of full sunlight) 0–100 %
- CO₂ concentration in the air 0–1000 ppm
- Leaf temperature 0–50 °C
- Graph x-axis CO₂, Light, Temperature
- Leaf shown inside Maize (C4), Wheat (C3)
- Highest day temperature 20–45 °C
- Lowest night temperature 5–30 °C
Questions to explore
- Above what temperature does maize fix CO₂ faster than wheat, and why?
- Why is the CO₂ compensation point of maize so much lower than that of wheat?
- When does the pineapple open its stomata to save water, and what does it pay for this?
