Chapter Summary: Photosynthesis in Higher Plants

Photosynthesis is the fundamental biological process by which green plants synthesise carbohydrates from CO₂ and H₂O using light energy in the presence of chlorophyll, releasing O₂ as a by-product.

Key Points at a Glance

1. Site of Photosynthesis

  • Occurs in chloroplasts
  • Light reactions → Thylakoid membranes (grana)
  • Dark reactions (Calvin cycle) → Stroma

2. Photosynthetic Pigments

  • Chlorophyll a: Reaction centre pigment
  • Chlorophyll b, carotenoids: Accessory pigments
  • Carotenoids protect chlorophyll from photooxidation

3. Light Reactions

  • Occur in presence of light
  • Include photolysis of water, ATP synthesis, and NADPH formation
  • Two photosystems: PS II (P680) and PS I (P700)
  • Follow Z-scheme of electron transport

4. Calvin Cycle (C₃ Pathway)

  • Takes place in stroma
  • Three phases: Carboxylation, Reduction, Regeneration
  • Primary CO₂ acceptor: RuBP
  • Key enzyme: RuBisCO

5. C₄ Pathway (Hatch and Slack Cycle)

  • First stable product: Oxaloacetic acid (OAA)
  • Initial CO₂ fixation by PEP carboxylase
  • Shows Kranz anatomy
  • Minimises photorespiration

6. Photorespiration (C₂ Cycle)

  • Occurs in C₃ plants
  • RuBisCO acts as oxygenase
  • Involves chloroplast, peroxisome, mitochondrion
  • Leads to loss of CO₂ and energy

7. Factors Affecting Photosynthesis

  • External: Light, CO₂, Temperature, Water
  • Internal: Chlorophyll content, leaf anatomy, enzymes
  • Blackman’s Law: Rate is limited by the factor in shortest supply

NEET Exam Tips: Photosynthesis in Higher Plants

🔑 High-Yield Areas (Very Frequently Asked)

  • Source of O₂ → Always H₂O (photolysis)
  • RuBisCO dual activity (carboxylase + oxygenase)
  • Difference between C₃ and C₄ plants
  • Kranz anatomy features
  • PEP carboxylase has no oxygenase activity

⚠️ Common NEET Traps

  • Confusing absorption spectrum with action spectrum
  • Assuming Calvin cycle requires light directly (it does NOT)
  • Thinking photorespiration produces ATP (it NEVER does)
  • Mixing up location of Calvin cycle (always stroma)

📌 Must-Memorise Facts

  • Reaction centre pigments: P680 (PS II), P700 (PS I)
  • Calvin cycle stoichiometry: 6 CO₂ → 18 ATP + 12 NADPH
  • Bundle sheath chloroplasts in C₄ plants are agranal

🧠 Smart MCQ Strategy

  • If options include PEP carboxylase, it usually points to C₄ pathway
  • Presence of three organelles → Think photorespiration
  • Questions with high temperature + low CO₂ → Expect photorespiration

📈 Revision Priority (Last 7 Days)

  1. C₃ vs C₄ comparison table
  2. Photorespiration pathway sequence
  3. Factors affecting photosynthesis + Blackman’s law
  4. PYQs from last 10 years (concepts repeat heavily)

✅ NEET Reality Check Photosynthesis is a guaranteed scoring chapter. Questions are mostly NCERT-direct, concept-based, and repetitive across years. Strong conceptual clarity + PYQ practice = full marks potential.