Photorespiration does not occur in C4 plants because they have a special mechanism that raises the CO2 level around the enzyme RuBisCO. In bundle sheath cells, C4 acids break down and release a lot of CO2. This high CO2 forces RuBisCO to act as a carboxylase and stops it from binding O2, so there is no photorespiration. Memory hook: "C4 pumps CO2 into a small room (bundle sheath) so RuBisCO cannot smell the oxygen."
C4 plants pump CO2 from mesophyll cells into tightly sealed bundle sheath cells. The high CO2 there keeps RuBisCO acting as a carboxylase and stops O2 from binding, so photorespiration does not occur.
Your doubts, answered
Why does photorespiration not occur in C4 plants?
Because C4 plants have a mechanism that increases the concentration of CO2 at the enzyme site (RuBisCO). The C4 acid made in mesophyll cells travels to the bundle sheath cells and breaks down there to release CO2. This makes the CO2 level very high around RuBisCO, so RuBisCO works only as a carboxylase and its oxygenase (O2-binding) activity is minimised. No O2 binding means no photorespiration.
What is the role of bundle sheath cells here?
Bundle sheath cells are the large cells around the vascular bundles in C4 plants (Kranz anatomy). They have many chloroplasts, thick walls that are impervious to gas exchange, and no intercellular spaces. The Calvin cycle runs only here. Because CO2 is released and trapped inside these tight cells, its concentration stays very high, keeping RuBisCO in carboxylase mode.
Then why does photorespiration happen in C3 plants?
C3 plants have no CO2-concentrating mechanism. Both O2 and CO2 compete for the same active site of RuBisCO. When O2 wins and binds RuBisCO, RuBP forms one phosphoglycerate + one phosphoglycolate instead of two PGA. This wasteful pathway is photorespiration. Because C4 plants keep CO2 high, O2 rarely wins, so they escape this loss.
Does photorespiration make ATP or sugar?
No. In the photorespiratory pathway there is no synthesis of sugar, ATP or NADPH. Instead it releases CO2 and uses up ATP. That is why it is a wasteful process, and avoiding it (like C4 plants do) gives higher productivity and yield.
Is the Calvin cycle also absent in C4 plants?
No, the Calvin (C3) cycle is present in all photosynthetic plants, including C4 plants. In C4 plants it simply runs only in the bundle sheath cells. What C4 plants avoid is photorespiration, not the Calvin cycle.
⚠️ The NEET trap ✗ C4 plants have no photorespiration because they do not contain RuBisCO. ✓ C4 plants do contain RuBisCO (in bundle sheath cells) and it stays active as a carboxylase. Photorespiration is avoided because CO2 is concentrated around RuBisCO, not because RuBisCO is missing. 🧠 NEET loves to swap 'no photorespiration' with 'no RuBisCO'. RuBisCO is present in C4 plants; only its oxygenase activity is minimised.
Real NEET questions
NEET 2016
The process which makes the major difference between C3 and C4 plants is:
A · Glycolysis
B · Calvin cycle
C · Photorespiration ✓
D · Respiration
Solution: Photorespiration occurs in C3 plants but not in C4 plants, so it is the process that separates the two groups. The Calvin cycle runs in both, so it cannot be the distinguishing process. Answer: Photorespiration.
NEET 2023
Statement I: RuBisCO is the most abundant enzyme in the world. Statement II: Photorespiration does not occur in C4 plants. Choose the most appropriate answer:
A · Both Statement I and Statement II are correct ✓
B · Both Statement I and Statement II are incorrect
C · Statement I is correct but Statement II is incorrect
D · Statement I is incorrect but Statement II is correct
Solution: RuBisCO is the most abundant enzyme/protein in the biosphere, so Statement I is correct. C4 plants concentrate CO2 around RuBisCO in bundle sheath cells, so photorespiration does not occur, making Statement II correct. Both are correct.
NEET 2024
Statement 1: In C3 plants, some O2 binds to RuBisCO, hence CO2 fixation is decreased. Statement 2: In C4 plants, mesophyll cells show very little photorespiration while bundle sheath cells do not show photorespiration. Choose the correct answer:
A · Both statements are false
B · Statement I is true but Statement II is false ✓
C · Statement I is false but Statement II is true
D · Both statements are true
Solution: Statement 1 is true: in C3 plants O2 competes with CO2 at RuBisCO, lowering CO2 fixation. Statement 2 is false: in C4 plants photorespiration does not occur at all, so the split of 'little' vs 'none' between mesophyll and bundle sheath is wrong. So only Statement I is true.
Solved Photosynthesis in Higher Plants NEET PYQs
Try the real previous-year questions from this chapter — each with the answer and a full solution.
Yes. NCERT states plainly that in C4 plants photorespiration does not occur, because the CO2-concentrating mechanism keeps RuBisCO working as a carboxylase.
Which cells concentrate CO2 in C4 plants?
The bundle sheath cells. C4 acids from the mesophyll break down here to release CO2, raising its concentration around RuBisCO.
Why is avoiding photorespiration useful?
Photorespiration makes no sugar, ATP or NADPH and wastes ATP while releasing CO2. Avoiding it gives C4 plants higher productivity, better yield and tolerance to high temperature.
Is RuBisCO present in C4 plants?
Yes, RuBisCO is present in the bundle sheath cells of C4 plants, where the Calvin cycle operates. It simply works mainly as a carboxylase due to high CO2.
What is a common NEET trap on this topic?
Confusing 'no photorespiration' with 'no RuBisCO' or 'no Calvin cycle'. C4 plants have both RuBisCO and the Calvin cycle; they only avoid photorespiration.
