Photosynthesis NEET PYQ Analysis: Calvin Cycle, C4 and Kranz

Quick answer: A photosynthesis NEET PYQ analysis shows that Photosynthesis in Higher Plants gives about two to three questions a year, and NTA keeps returning to five areas: the Calvin cycle (RuBisCO, 3-PGA, and the ATP and NADPH needed), the C4 pathway with Kranz anatomy, photorespiration, the light reaction (photosystems, cyclic vs non-cyclic photophosphorylation and the chemiosmotic hypothesis), and pigments with early experiments. The 2024, 2025 and 2026 papers all asked Calvin cycle questions.

Photosynthesis NEET PYQ analysis showing sunlight on maize leaves and oxygen bubbles rising from a water plant

This guide breaks down what NTA repeats, the tables to memorise and PYQ-pattern questions with answers. For the full plant physiology plan, see our plant physiology guide for NEET.

Want to test yourself first? Solve the Photosynthesis PYQs for free, then use this guide to fix the gaps.

Why Photosynthesis Is a Must-Score Chapter

With more than 90 past questions, Photosynthesis in Higher Plants is one of the biggest PYQ banks in Class 11 Botany, and its questions are mostly numbers and comparisons you can learn: 3 ATP and 2 NADPH per CO₂, P680 and P700, C3 vs C4. For chapter notes, use our Photosynthesis class 11 notes, and to see where it sits among other chapters, check the NEET 2027 chapter weightage.

The leaf structure behind Kranz anatomy is in our Plant Anatomy PYQ analysis, and chloroplast structure is in our Cell PYQ analysis.

Photosynthesis NEET PYQ Analysis: What NTA Repeats

When you sort the past NEET biology PYQs from this chapter, five question types cover nearly everything.

Question type	Frequency	What it tests
Calvin cycle	Most frequent	RuBisCO, 3-PGA, three stages, ATP and NADPH per CO₂ and per glucose
C4 pathway and Kranz anatomy	Very frequent	PEP, PEP carboxylase, OAA, bundle sheath cells, examples
Light reaction	Very frequent	PS I and PS II, photolysis, cyclic vs non-cyclic photophosphorylation, chemiosmosis
Photorespiration	Regular	Oxygenase activity of RuBisCO, why C4 plants avoid it
Pigments and early experiments	Regular	Pigment colours, Priestley, Ingenhousz, Engelmann, van Niel

For a quick warm-up, try these five quick plant physiology questions.

Early Experiments

Scientist	Finding
Joseph Priestley (1770)	A mint plant restored air that a burning candle or a mouse had used up
Jan Ingenhousz	Sunlight is needed, and only the green parts release oxygen
Julius von Sachs (1854)	Glucose is made and stored as starch; chlorophyll is in chloroplasts
T.W. Engelmann	Using Cladophora, a prism and aerobic bacteria, showed most oxygen is released in blue and red light (the first action spectrum)
Cornelius van Niel	From purple and green sulphur bacteria, showed that the O₂ released comes from water, not CO₂

The correct overall equation is 6CO₂ + 12H₂O → C₆H₁₂O₆ + 6H₂O + 6O₂.

Pigments

Paper chromatography separates four leaf pigments:

Pigment	Colour on the chromatogram
Chlorophyll a	Bright or blue-green
Chlorophyll b	Yellow-green
Xanthophylls	Yellow
Carotenoids	Yellow to yellow-orange

Chlorophyll a is the chief pigment. The others are accessory pigments: they absorb a wider range of wavelengths and protect chlorophyll a from photo-oxidation.

The Light Reaction

The light reaction happens in the grana (thylakoids) of the chloroplast. Its products are ATP, NADPH and O₂.

Feature	Photosystem I	Photosystem II
Reaction centre	P700	P680
Role	Passes electrons to NADP⁺	Linked to photolysis of water

Photolysis: the water-splitting complex is linked to PS II on the inner (lumen) side of the thylakoid membrane: 2H₂O → 4H⁺ + O₂ + 4e⁻.

Feature	Non-cyclic photophosphorylation	Cyclic photophosphorylation
Photosystems used	PS II and PS I (Z scheme)	PS I only
Products	ATP and NADPH	ATP only
Where	Grana	Stroma lamellae (which lack PS II and NADP reductase)
When	Normal conditions	When only light beyond 680 nm is available

Chemiosmotic hypothesis: protons build up inside the thylakoid lumen because water is split there, the cytochrome b₆f complex moves protons into it, and NADP reductase removes protons from the stroma. The proton gradient drives H⁺ back through ATP synthase, whose CF₀ part forms the channel through the membrane and whose CF₁ part sticks into the stroma and makes ATP.

The Calvin Cycle (C3 Pathway)

Melvin Calvin used radioactive ¹⁴C to show that the first stable product is the 3-carbon 3-phosphoglyceric acid (3-PGA). The Calvin cycle happens in the stroma and has three stages:

Carboxylation: RuBisCO fixes CO₂ onto ribulose bisphosphate (RuBP), giving two molecules of 3-PGA.
Reduction: 3-PGA is reduced to carbohydrate using ATP and NADPH.
Regeneration: RuBP is regenerated, using more ATP.

To fix	ATP	NADPH	Turns of the cycle
One CO₂	3	2	1
One glucose	18	12	6

The 3 ATP and 2 NADPH per CO₂ figure has been asked in several recent papers, including 2024 and 2026.

The C4 Pathway and Kranz Anatomy

In the C4 pathway (Hatch and Slack pathway), CO₂ is first fixed in the mesophyll and then released in the bundle sheath.

Feature	C3 plants	C4 plants
Primary CO₂ acceptor	RuBP (5C)	PEP (3C)
First stable product	3-PGA (3C)	Oxaloacetic acid, OAA (4C)
Enzyme of first fixation	RuBisCO	PEP carboxylase (PEPcase)
Cells doing the Calvin cycle	Mesophyll	Bundle sheath
Wreath of bundle sheath cells	Absent	Present
Photorespiration	Present	Absent
Examples	Rice, wheat	Maize, sorghum

Kranz anatomy: large bundle sheath cells form a wreath around the vascular bundles. They have many chloroplasts, thick walls that block gas exchange, and no intercellular spaces. Mesophyll cells of C4 plants lack RuBisCO.

Photorespiration

RuBisCO can bind O₂ as well as CO₂. When it binds O₂, RuBP gives one 3-PGA and one phosphoglycolate. Photorespiration makes no sugar and no ATP; it uses up ATP instead. C4 plants avoid it because they concentrate CO₂ in the bundle sheath, so RuBisCO acts mainly as a carboxylase there. RuBisCO is the most abundant enzyme in the world.

Factors Affecting Photosynthesis

Blackman’s law of limiting factors (1905): when a process depends on several factors, its rate is set by the one nearest its minimum value.
Light saturation happens at about 10% of full sunlight, so light rarely limits plants in nature, except in shade or dense forests.
CO₂ is the major limiting factor. C3 plants respond to higher CO₂ and saturate only beyond about 450 µL/L, while C4 plants saturate at about 360 µL/L. This is why tomatoes and bell peppers give higher yields in CO₂-enriched greenhouses.

Worked PYQ-Pattern Questions

Q1. The first stable product of CO₂ fixation in C4 plants is: (a) 3-PGA (b) Oxaloacetic acid (c) Malic acid (d) RuBP

Answer: (b) Oxaloacetic acid, a 4-carbon compound. In C3 plants it is 3-PGA.

Q2. How many ATP and NADPH are needed to make one glucose molecule through the Calvin cycle?

Answer: 18 ATP and 12 NADPH, from six turns at 3 ATP and 2 NADPH per CO₂.

Q3. Cyclic photophosphorylation: (a) Uses PS II only (b) Produces ATP and NADPH (c) Produces only ATP and involves only PS I (d) Releases O₂

Answer: (c). It happens in the stroma lamellae, which lack PS II.

Q4. The oxygen released in photosynthesis comes from water. Who showed this?

Answer: Cornelius van Niel, working with purple and green sulphur bacteria.

Q5. Why is photorespiration absent in C4 plants?

Answer: C4 plants concentrate CO₂ around RuBisCO in the bundle sheath cells, so the enzyme works as a carboxylase and not an oxygenase.

Q6. On a chromatogram, chlorophyll b appears:

Answer: Yellow-green. Chlorophyll a appears bright or blue-green.

Common Traps in This Chapter

Writing 3-PGA as the first product in C4 plants (it is OAA)
Saying the Calvin cycle happens in the grana (it happens in the stroma)
Linking photolysis with PS I instead of PS II
Saying cyclic photophosphorylation makes NADPH
Placing the Calvin cycle of C4 plants in mesophyll cells
Saying the O₂ released comes from CO₂

Practise Every Photosynthesis PYQ

This photosynthesis NEET PYQ analysis shows you where the marks are. Solving real past questions makes the numbers and comparisons automatic. Every Photosynthesis in Higher Plants previous year question is available chapter-wise, free:

👉 Solve all Photosynthesis NEET PYQs

Keep the C3 vs C4 and photophosphorylation tables beside you for the first round, then solve the second round without them.

Conclusion

Photosynthesis in Higher Plants has a large PYQ bank, but its questions keep returning to the same numbers and comparisons. Use this photosynthesis NEET PYQ analysis to master the Calvin cycle, the C4 pathway and Kranz anatomy, photorespiration and the light reaction. Then practise the past questions until each answer comes without thinking.

❓ FAQ

Q: How many questions come from Photosynthesis in NEET? A: Usually two to three questions a year, mostly on the Calvin cycle, the C4 pathway, photorespiration and the light reaction.

Q: What is the most important topic in Photosynthesis for NEET? A: The Calvin cycle, especially RuBisCO, 3-PGA and the 3 ATP and 2 NADPH needed per CO₂. The C4 pathway comes next.

Q: What is the difference between cyclic and non-cyclic photophosphorylation? A: Non-cyclic uses both photosystems and makes ATP and NADPH. Cyclic uses only PS I, happens in the stroma lamellae and makes only ATP.

Q: What is Kranz anatomy? A: The arrangement in C4 leaves where large bundle sheath cells with many chloroplasts, thick walls and no intercellular spaces form a wreath around each vascular bundle.

Q: Why do C4 plants not show photorespiration? A: They concentrate CO₂ in the bundle sheath cells, so RuBisCO works as a carboxylase there.

Q: Where can I practise Photosynthesis NEET PYQs for free? A: You can solve every Photosynthesis in Higher Plants previous year question chapter-wise for free using the practice links in this article.