NEET Biology · Photosynthesis PYQ
NEET Photosynthesis in Higher Plants PYQ (2005–2025)
Photosynthesis is a P1 NEET Biology chapter — ~4% weightage on trend, often 1–2 questions per paper. It anchors Plant Physiology and is NCERT-diagram-intensive. The Z-scheme, Calvin cycle and C3-vs-C4 comparisons are the three most-repeated question categories.
Photosynthesis PYQs spanning AIPMT 2005 to NEET 2025, tagged by sub-topic (light reactions, dark reactions, C3/C4, photorespiration). Every solution cites NCERT Class 11 Chapter 13 line or figure references.
Photosynthesis in Higher Plants at a Glance
Key Sub-Topics & What's Tested
Chloroplast Structure
Double membrane, stroma, grana, thylakoids, stroma lamellae, chlorophyll location, NCERT diagram memorisation.
Pigments in Photosynthesis
Chlorophyll a, b, carotenoids, xanthophylls, absorption spectrum (chlorophyll a peaks at 430 and 662 nm), action spectrum.
Light Reactions (Z-Scheme)
PS I and PS II, electron transport chain, water splitting at PS II, NADPH formation, ATP synthesis (photophosphorylation).
Cyclic vs Non-Cyclic Photophosphorylation
Non-cyclic involves both PS I and PS II, produces NADPH + ATP. Cyclic involves only PS I, produces only ATP.
Dark Reactions — Calvin Cycle (C3)
RuBP + CO₂ → 2 × 3-PGA (Rubisco), reduction phase (G3P formation), regeneration of RuBP, overall stoichiometry.
C4 Pathway
Kranz anatomy, PEP carboxylase in mesophyll, oxaloacetate → malate → bundle sheath → CO₂ concentration + Calvin cycle.
Photorespiration
Occurs in C3 plants at high O₂ / low CO₂ / high temperature, wasteful process, absent in C4 plants (advantage).
Factors Affecting Photosynthesis
Light intensity, CO₂ concentration, temperature, water — Blackman's law of limiting factors, optimum conditions.
Question Type Distribution
| Question Type | Share (approx) | Example Pattern |
|---|---|---|
| Light vs Dark Reaction Identification | 25% | Which of the following occurs only in light reactions? (ATP production, NADPH formation, photolysis) |
| C3 vs C4 Comparison | 20% | Kranz anatomy is found in which type of plants? Why are C4 plants more efficient? |
| Z-Scheme / Electron Flow | 15% | Arrange the components of Z-scheme in correct sequence. |
| Chloroplast Structure | 15% | Which membrane contains electron transport components? (thylakoid membrane) |
| Pigment Absorption / Action Spectrum | 15% | Which wavelength is least absorbed by chlorophyll a? |
| Calvin Cycle Steps | 10% | Identify the primary acceptor of CO₂ in C3 plants. (RuBP) |
How to Solve Photosynthesis in Higher Plants PYQs
- 1Memorise the chloroplast diagram from NCERT. Outer membrane, inner membrane, thylakoid, granum, stroma lamella, stroma — locations of each photosynthesis step matters.
- 2Z-scheme: know the order strictly. PS II (water splitting, O₂ released) → plastoquinone → cytochrome complex → plastocyanin → PS I → ferredoxin → NADP⁺ → NADPH.
- 3C3 vs C4 comparison: Kranz anatomy + enzymes. C3: Rubisco in mesophyll. C4: PEP carboxylase in mesophyll + Rubisco in bundle sheath. Kranz = C4 marker.
- 4Photolysis of water: at PS II, not PS I. 2H₂O → 4H⁺ + 4e⁻ + O₂. Light-dependent, generates electrons for PS II and oxygen as by-product.
- 5Cyclic vs non-cyclic: products determine identification. Non-cyclic: ATP + NADPH + O₂ (complete). Cyclic: only ATP (no NADPH, no O₂). ATP:NADPH ratio in cyclic is variable.
Common Mistakes That Cost Marks
- Thinking light reactions happen in stroma. Light reactions occur on thylakoid membrane. Dark reactions (Calvin cycle) occur in stroma.
- Confusing Z-scheme electron flow direction. Electrons flow from water → PS II → PS I → NADP⁺ (energy-wise UP the Z). Never backward to water.
- Calling Calvin cycle 'dark reactions' as if they need dark. They occur in stroma (can happen in light). Called 'dark' because they don't directly require light photons.
- C4 plants as 'better than C3' everywhere. C4 is adapted for hot, dry, high-light conditions. C3 is better in cool, moist, low-light environments.
- Photorespiration occurring in C4 plants. Photorespiration is essentially absent in C4 plants because Kranz anatomy concentrates CO₂ around Rubisco, suppressing oxygenase activity.
Related NEET Practice
Frequently asked questions
How many Photosynthesis PYQs should I solve?
Target 60–80 PYQs across AIPMT 2005 to NEET 2025. Given its ~4% weightage on trend and heavy NCERT derivation, consistent practice builds recall for direct-line questions.
Is NCERT Class 11 Chapter 13 enough?
Yes — NCERT + chapter PYQs is sufficient for 17–20/20 in this chapter. NCERT diagrams are exactly what NTA tests.
What's the most-tested Photosynthesis PYQ pattern?
C3 vs C4 plant comparison — Kranz anatomy, enzyme, efficiency, examples. Roughly 4–5 variants per 10-year window. Master this pattern.
Do I need to memorise all enzymes in Calvin cycle?
Primary ones: Rubisco (CO₂ fixation), PEP carboxylase (C4). Phosphoglycerate kinase, glyceraldehyde-3-phosphate dehydrogenase — know names and roles but detailed mechanisms aren't in the NEET syllabus.
How many ATP molecules are needed to produce one glucose?
30 ATP (simplified: 18 ATP for Calvin cycle + 6 ATP regenerating RuBP, with variations in NCERT computations). NCERT states approximate totals; question may ask net or gross.
Why do tropical crops use C4 pathway?
High light intensity + high temperature + low water availability. C4 plants conserve water and reduce photorespiration — sugarcane, maize, sorghum are classic C4 examples.
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