Quick answer: Photosynthesis in Higher Plants is a 2-question chapter in NEET, mostly on the Z-scheme, Calvin cycle counts and C3 vs C4 differences.
Site and pigments
- Chloroplast: light reactions in thylakoid membranes (grana), dark reactions in stroma.
- Pigments: chlorophyll a (main, blue-green), chlorophyll b (yellow-green), xanthophylls, carotenoids (accessory, protect from photo-oxidation).
- Action spectrum peaks in blue and red (Engelmann’s experiment).
Light reaction
- PS II (P680) and PS I (P700). Water splitting at PS II (Mn, Ca, Cl⁻) releases O₂.
- Non-cyclic (Z-scheme): PS II → PQ → cyt b₆f → PC → PS I → Fd → NADP⁺ reductase; produces ATP + NADPH + O₂.
- Cyclic: PS I only, produces ATP only (in stroma lamellae, lacks PS II and NADP reductase).
- Chemiosmosis: proton gradient across thylakoid drives ATP synthase (CF₀–CF₁).
Calvin cycle (C3)
- Three steps: carboxylation (RuBisCO: RuBP + CO₂ → 2 × 3-PGA), reduction (ATP + NADPH → triose phosphate), regeneration of RuBP (ATP).
- For 1 glucose: 6 CO₂, 18 ATP, 12 NADPH; per CO₂: 3 ATP, 2 NADPH.
C4 and CAM
| C3 | C4 | CAM | |
|---|---|---|---|
| First product | 3-PGA | OAA (4C) | OAA (night) |
| CO₂ acceptor | RuBP | PEP | PEP |
| Enzyme | RuBisCO | PEP carboxylase (mesophyll) then RuBisCO (bundle sheath) | PEP carboxylase at night |
| Kranz anatomy | No | Yes | No |
| Photorespiration | Yes | Negligible | Low |
| Examples | Wheat, rice | Maize, sugarcane, sorghum | Cactus, pineapple |
Factors
- Blackman’s law of limiting factors; CO₂ is usually limiting; C4 plants saturate at lower CO₂ and tolerate higher temperature.
- Photorespiration: RuBisCO with O₂ → no sugar, ATP lost.
Common mistakes
- Saying cyclic photophosphorylation makes NADPH
- Writing 12 ATP for one glucose (it is 18)
- Placing Kranz anatomy in C3 plants
Related: Cell notes.
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Frequently asked questions
Is this Photosynthesis NEET Notes content at JEE/NEET level?
Yes. It covers the formulas, facts and question types that appear in JEE Main, JEE Advanced and NEET, with the NCERT base that these exams follow.
How many questions come from Photosynthesis NEET Notes?
Typically one to three questions per paper, depending on the year. Check the chapter-wise weightage post and give this topic time in proportion.
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