Summary
A pathway that concentrates CO2 in bundle sheath cells to reduce photorespiration in hot climates, as in maize.
In depth
Mesophyll cells fix CO2 with PEP carboxylase to form 4-carbon acids; these move to bundle sheath cells where CO2 is released near rubisco, reducing photorespiration. It uses extra ATP but is more efficient in heat and light.
The spatial separation of initial fixation and Calvin cycle reduces photorespiration. It has evolved independently over 60 times. It costs two extra ATP per CO2 but wins above about 30 °C.
Common mistake: C4 plants still use rubisco and the Calvin cycle.
C4 plants (maize, sugar cane, sorghum, many tropical grasses) have Kranz anatomy, with bundle sheath cells surrounding veins. PEP carboxylase has no affinity for oxygen, and the pump raises CO2 around rubisco about tenfold, almost eliminating photorespiration. The cost is extra ATP (about 2 per CO2), so C4 is advantageous in hot, bright, dry conditions but not in cool or shaded ones. Water use efficiency is also better, as stomata can be partly closed.
C4 evolved independently over 60 times, mostly in the last 30 million years as CO2 fell. About 3 percent of plant species are C4 but they account for around 25 percent of land productivity. Projects aim to engineer C4 traits into rice to raise yields.
Remember: the first stable product is a four-carbon acid (oxaloacetate), hence C4.
Frequently asked questions
What is C4 Photosynthesis?
A pathway that concentrates CO2 in bundle sheath cells to reduce photorespiration in hot climates, as in maize.
Which area of biology covers C4 Photosynthesis, and how advanced is it?
C4 Photosynthesis is one of the 56 topics in Plant Biology. It is rated Advanced, so it suits learners who want specialist depth. Related topics in this area include Rubisco, Photosynthesis Efficiency Engineering, Photosynthesis.
Can you give an example of C4 Photosynthesis?
Maize, sugarcane and sorghum.
What should I learn before C4 Photosynthesis?
Work through the Beginner topics in Plant Biology first, such as Plant Kingdom, Photosynthesis, Chlorophyll, then return to C4 Photosynthesis. Advanced topics assume the Intermediate vocabulary.
What topics are related to C4 Photosynthesis?
The closest topics to C4 Photosynthesis are Rubisco, Photosynthesis Efficiency Engineering, Photosynthesis, Plant Kingdom. Comparing them side by side is a good way to see how the ideas connect.
How can I check that I understand C4 Photosynthesis?
Read the summary and the in-depth section, then use the quick check on the interactive lesson for C4 Photosynthesis. To practise the whole of Plant Biology, use the Plant Biology quiz.
How is C4 Photosynthesis different from Rubisco?
C4 Photosynthesis: A pathway that concentrates CO2 in bundle sheath cells to reduce photorespiration in hot climates, as in maize. Rubisco: The enzyme that fixes carbon dioxide in the Calvin cycle and is likely the most abundant protein on Earth. Read both side by side and note what each one explains.
What is a common mistake about C4 Photosynthesis?
C4 plants still use rubisco and the Calvin cycle.
How should I study C4 Photosynthesis step by step?
First, read the summary and write the definition in your own words. Second, read the in-depth section and note any example. Third, compare it with Rubisco and explain the difference aloud. Finally, take the Plant Biology quiz and come back to this page for any question you miss.