Last Updated: May 2026
Photosynthesis in Higher Plants is one of the highest-yield chapters for NEET Biology — typically worth 3-5 questions in NEET UG every year. The chapter sits at the intersection of NCERT Class 11 Biology Chapter 13 and NCERT Class 12 Plant Physiology concepts. NEET examiners test fact-recall (where Calvin Cycle was discovered, names of pigments, products of light reaction) along with applied numerical (P/2e ratio, ATP yield). This guide covers every NCERT line that has appeared in NEET papers over 2018-2026 and provides 40 fresh practice MCQs.
Quick Facts — Photosynthesis
| Aspect | Detail |
|---|---|
| Site (cellular) | Chloroplast (thylakoid membrane + stroma) |
| Discoverer of Calvin Cycle | Melvin Calvin (Nobel Prize 1961) |
| First C4 plant identified | Sugarcane (Hatch and Slack 1966) |
| Wavelength range used | 400-700 nm (PAR — Photosynthetically Active Radiation) |
| Net products of light reaction | ATP, NADPH, O₂ |
| Net product of dark reaction | Glucose (C₆H₁₂O₆) |
1. Site of Photosynthesis
Photosynthesis occurs in the chloroplast, a double-membrane plastid in green cells. The thylakoid disks (grana) house light-harvesting pigments and carry out the light reaction; the surrounding fluid stroma hosts enzymes that drive the dark reaction (Calvin cycle).
2. Photosynthetic Pigments
| Pigment | Colour Absorbed | Colour Reflected |
|---|---|---|
| Chlorophyll a | Blue-violet, red | Bluish-green |
| Chlorophyll b | Blue, orange-red | Yellow-green |
| Carotenoids (β-carotene, xanthophyll) | Blue, blue-green | Yellow, orange |
Chlorophyll a is the primary pigment / reaction-centre pigment. Carotenoids are accessory pigments that protect against photo-oxidation.
3. Photosystems I and II
- Photosystem II (PS II) — P680: Reaction-centre pigment absorbs maximally at 680 nm; carries out water photolysis; produces O₂.
- Photosystem I (PS I) — P700: Reaction-centre absorbs at 700 nm; primary acceptor is ferredoxin; reduces NADP⁺ to NADPH.
4. Light Reaction — Z-scheme
The path of electron flow:
H₂O → PS II (P680) → Plastoquinone → Cyt b₆-f complex → Plastocyanin → PS I (P700) → Ferredoxin → NADP⁺ reductase → NADPH
Two ATP per electron pair are made via the chemiosmotic hypothesis — proton gradient across the thylakoid membrane drives ATP synthase.
5. Photolysis of Water
2H₂O → 4H⁺ + 4e⁻ + O₂. The Mn₄Ca cluster (Oxygen Evolving Complex) on the lumenal side of PS II carries out this reaction. Source of all O₂ in the atmosphere is photosynthesis (Hill 1937).
6. Cyclic vs Non-cyclic Photophosphorylation
| Feature | Non-cyclic | Cyclic |
|---|---|---|
| Photosystems involved | PS I + PS II | PS I only |
| Electron acceptor | NADP⁺ | Returns to PS I |
| NADPH formed? | Yes | No |
| O₂ released? | Yes | No |
| Site | Granal thylakoid | Stromal thylakoid |
7. Calvin Cycle — The Dark Reaction
Three phases: Carboxylation, Reduction, Regeneration.
- Carboxylation: RuBisCO catalyses RuBP + CO₂ → 2 × 3-PGA.
- Reduction: 3-PGA → 1,3-BPG → G3P (uses 6 ATP and 6 NADPH per 3 CO₂).
- Regeneration: 5 G3P + 3 ATP → 3 RuBP.
Net for 1 glucose: 18 ATP + 12 NADPH + 6 CO₂ + 6 RuBP → 1 glucose + 6 RuBP regenerated.
8. C3 vs C4 vs CAM Plants
| Feature | C3 | C4 | CAM |
|---|---|---|---|
| Initial fixation | RuBP + CO₂ → PGA (3-C) | PEP + CO₂ → OAA (4-C) | PEP + CO₂ at night |
| Anatomy | No Kranz | Kranz anatomy (bundle sheath) | Stomata open at night |
| Examples | Wheat, rice | Maize, sugarcane, sorghum | Pineapple, cactus, opuntia |
| Optimum temperature | 20-25°C | 30-45°C | Hot dry climate |
| Photorespiration | Yes | Negligible | Negligible |
9. Photorespiration
RuBisCO has affinity for both CO₂ and O₂. In hot dry conditions, O₂ predominates and RuBP + O₂ → 1 PGA + 1 phosphoglycolate. Phosphoglycolate is converted to glycine in peroxisomes and finally to serine in mitochondria — releasing CO₂. Net result: energy loss without sugar gain.
10. Factors Affecting Photosynthesis (Blackman’s Law of Limiting Factor)
- Light intensity — increases rate up to saturation.
- CO₂ concentration — rate increases up to ~360 ppm in C3.
- Temperature — optimum 25-35°C.
- Water — affects stomatal conductance.
40 Practice MCQs (Sample of 10 — Full Set Linked Below)
Q1. The site of photolysis is — (a) Stroma (b) Cytoplasm (c) Inner side of thylakoid (d) Cristae of mitochondria. Ans: (c) Lumen / inner side of thylakoid (Mn₄Ca cluster of PS II).
Q2. RuBisCO stands for — (a) Ribulose-1,5-bisphosphate carboxylase/oxygenase (b) Ribose-5-phosphate carbonase (c) Ribitol bisphosphate carboxylase (d) Ribulose monophosphate enzyme. Ans: (a)
Q3. Number of ATP molecules required for the synthesis of one glucose molecule in the Calvin cycle is — (a) 12 (b) 18 (c) 24 (d) 36. Ans: (b)
Q4. Kranz anatomy is found in — (a) Wheat (b) Rice (c) Sugarcane (d) Pineapple. Ans: (c)
Q5. Hill reaction demonstrates — (a) That photosynthesis occurs in chloroplasts (b) That isolated chloroplasts can release O₂ when supplied with H₂O and an electron acceptor in the presence of light (c) Existence of cyclic photophosphorylation (d) Existence of bacterial photosynthesis. Ans: (b) Hill 1937.
Q6. The first stable product of C4 cycle is — (a) PGA (3 carbon) (b) OAA (4 carbon) (c) Malic acid (d) RuBP. Ans: (b)
Q7. Photorespiration occurs in — (a) Chloroplast only (b) Chloroplast, peroxisome and mitochondria (c) Cytoplasm only (d) Endoplasmic reticulum. Ans: (b)
Q8. Cyclic photophosphorylation produces — (a) ATP only (b) NADPH only (c) ATP and NADPH (d) Glucose. Ans: (a)
Q9. The reaction-centre pigment of PS I is — (a) P680 (b) P700 (c) Chlorophyll b (d) β-carotene. Ans: (b)
Q10. Calvin Cycle was discovered using which radioactive tracer — (a) ³²P (b) ¹⁴C (c) ³⁵S (d) ¹⁵N. Ans: (b) ¹⁴CO₂.
Frequently Asked Questions
How many questions from photosynthesis come in NEET?
3-5 questions every year, mostly from NCERT Class 11 Biology Chapter 13. Topics rotate among Calvin cycle, C3 vs C4, photorespiration and Hill reaction.
Is the Z-scheme important?
Yes. Diagram-based questions on the Z-scheme appear once every two years. Memorise the order: H₂O → PS II → PQ → Cyt b₆-f → PC → PS I → Fd → NADP⁺.
Why are C4 plants more efficient than C3?
C4 plants concentrate CO₂ around RuBisCO via the bundle sheath, suppressing photorespiration. They also tolerate higher temperatures, making them more productive in tropical climates.
Are CAM plants the same as C4 plants?
No. Both fix CO₂ via PEP carboxylase, but CAM plants temporally separate the two stages (night fixation, day decarboxylation), while C4 plants spatially separate (mesophyll vs bundle sheath).
What is the optimum temperature for C3 photosynthesis?
20-25 degrees Celsius. Above this, photorespiration becomes significant and net photosynthesis declines.