Photosynthesis in Higher Plant Handwritten Notes for neet class 11th

Description

• Definition: Photosynthesis is the process by which green plants, algae, and some bacteria convert light energy into chemical energy, stored in glucose.
• General Equation: 6CO2+12H2O+light energy→C6H12O6+6O2+6H2O6CO_2 + 12H_2O + text{light energy} rightarrow C_6H_{12}O_6 + 6O_2 + 6H_2O6CO2​+12H2​O+light energy→C6​H12​O6​+6O2​+6H2​O

2. Structure of Chloroplast

• Chloroplast: The site of photosynthesis in plant cells.
  • Double Membrane: Outer and inner membranes.
  • Stroma: Fluid-filled matrix inside chloroplasts.
  • Thylakoids: Membrane-bound structures within the stroma, stacked to form grana.
  • Grana: Stacks of thylakoids.
  • Lamellae: Connect grana.
  • Photosynthetic Pigments: Chlorophyll a, Chlorophyll b, Carotenoids.

3. Light Reaction (Photochemical Phase)

• Occurs in Thylakoid Membranes.
• Photosystems:
  • Photosystem I (PS I)
  • Photosystem II (PS II)
• Process:
  • Absorption of light energy.
  • Water splitting (Photolysis) in PS II: 2H2O→4H++4e−+O22H_2O rightarrow 4H^+ + 4e^- + O_22H2​O→4H++4e−+O2​
  • Electron Transport Chain (ETC)
  • Formation of ATP (Photophosphorylation) and NADPH.

4. Dark Reaction (Calvin Cycle/Biosynthetic Phase)

• Occurs in Stroma.
• Three Phases:
  • Carboxylation: CO_2 is fixed into a stable intermediate. RuBP+CO2→2×3−PGAtext{RuBP} + CO_2 rightarrow 2 times 3-PGARuBP+CO2​→2×3−PGA
  • Reduction: ATP and NADPH from light reactions are used to convert 3-PGA into G3P.
  • Regeneration: G3P is used to regenerate RuBP, allowing the cycle to continue.
• End Product: Glucose.

5. C_4 Pathway (Hatch-Slack Pathway)

• Occurs in C_4 plants like maize, sugarcane.
• Anatomy: Kranz anatomy (specialized leaf structure).
• Steps:
  • Mesophyll Cells: CO_2 is fixed into a 4-carbon compound (OAA) by PEP carboxylase.
  • Bundle Sheath Cells: OAA is transported and decarboxylated to release CO_2 for the Calvin cycle.
  • CAM Pathway (Crassulacean Acid Metabolism)
  • Occurs in succulent plants like cacti.
  • Adaptation to arid conditions.
  • Process:
  • Stomata open at night, CO_2 is fixed into organic acids.
  • Stomata close during the day, CO_2 is released from organic acids for the Calvin cycle.
  • 7. Factors Affecting Photosynthesis
  • Light Intensity: Rate of photosynthesis increases with light intensity up to a certain point.
  • Carbon Dioxide Concentration: Higher CO_2 levels increase the rate of photosynthesis.
  • Temperature: Optimal temperature range for enzyme activity.
  • Water: Essential for photolysis in light reactions.
  • Chlorophyll Content: More chlorophyll increases the plant’s ability to capture light energy.
  • 8. Significance of Photosynthesis
  • Primary Source of Energy: Converts solar energy into chemical energy.
  • Produces Oxygen: Essential for respiration in aerobic organisms.
  • Carbon Cycle: Fixes carbon dioxide into organic molecules.
  • 9. Comparison of C_3, C_4, and CAM Pathways
  • C_3 Pathway: Most common, direct Calvin cycle, inefficient under high light intensity and temperatures.
  • C_4 Pathway: Adapted to high light intensity and temperatures, separates initial CO_2 fixation and Calvin cycle.
  • CAM Pathway: Adapted to arid conditions, temporal separation of CO_2 fixation and Calvin cycle.