Question

All plants use the Calvin Cycle to incorporate CO₂ into simple sugars. C₃ plants (typical plants) obtain their CO₂ directly from the atmosphere but not without a cost. Explain this trade-off. What do C₄ plants and CAM plants do differently (in general) and why do they do it? Where do these species typically live? Why don’t all species use the C₄ or CAM photosynthetic process? In other words, what is the cost of doing C₄ or CAM photosynthesis?

Answer 1

Question

Plants use carbon-dioxide and convert this carbon-dioxide into simple sugar that is glucose with the help of Calvin cycle. The energy require for carbon-fixation is 18 ATP that were generated during light reaction. This amount of ATP generated effectively in minimal light reaction. So, very less cost is required to run the Calvin-cycle.

C4 and CAM plants are more effective than C3 plants because they do not undergo the process of photorespiration. They inhibit the oxygenase activity of Rubisco enzyme. The C4 and CAM plants have different anatomy , to inhibit the activity of oxygenase activity of Rubisco. In order to perform this activity, C4 and CAM plants , have to spend large amount of ATP that is equal to 30 ATP, that is much higher than C3 plants. These plants live in less water in soil condition . All plants do not use CAM or C4 pathway because these pathways do use more ATP as compare to Calvin cycle pathway. The cost of performing CAM and C4 is 30 ATP , that is approximate double of the cost of performing Calvin cycle which is 18 ATP.