Photosynthesis Overview

Definition

• Photosynthesis: The process of using light energy to build carbohydrates like glucose.
• Key terms:
  • Photo: Light
  • Synthesis: To build

Photosynthesis Equation

• Reactants: 6 H₂O (water) + 6 CO₂ (carbon dioxide)
• Products: C₆H₁₂O₆ (glucose) + O₂ (oxygen gas)

Process Overview

• Water: Enters plant through roots.
• Carbon Dioxide: Enters leaves via stomata.
• Oxygen: Leaves plant through stomata.

Organelles Involved

• Chloroplasts: Site of photosynthesis.
• Mitochondria: Site of cellular respiration (opposite process).

Pigments and Light Absorption

• Chlorophyll: Absorbs blue and red light, reflects green.
• Location: Found in thylakoids within chloroplasts.

Chloroplast Structure

• Thylakoids: Stacked into grana (singular: granum).
• Stroma: Fluid inside chloroplast.
• Two Membranes: Inner and outer, with intermembrane space.

Photosynthesis Stages

Light-Dependent Reactions

• Location: Thylakoid membranes.
• Reactants: Water, NADP⁺, ADP, and phosphate.
• Products: Oxygen gas, ATP, and NADPH.
• Key Processes:
  • Oxidation: Water to oxygen gas.
  • Reduction: NADP⁺ to NADPH.
  • ATP Production: Through chemiosmosis and ATP synthase.
• Photosystems:
  • Photosystem II (P680): Converts water to oxygen, absorbs 680 nm light.
  • Photosystem I (P700): Absorbs 700 nm light.

Light-Independent Reactions (Calvin Cycle)

• Location: Stroma of the chloroplast.
• Reactants: CO₂, ATP, NADPH.
• Products: Sugars like glucose, NADP⁺, ADP, and phosphate.
• Key Phases:
  • Carbon Fixation: CO₂ reacts with RuBP (ribulose bisphosphate) via Rubisco enzyme.
  • Reduction: Uses ATP and NADPH to form G3P (glyceraldehyde-3-phosphate).
  • Regeneration: RuBP is regenerated to continue the cycle.
• Net Result: Converts 3 CO₂ to 1 G3P. Requires 9 ATP and 6 NADPH.
• Glucose Production: Needs 6 CO₂, 18 ATP, 12 NADPH for 2 G3P (forms 1 glucose).

Summary

• Photosynthesis consists of two main processes:
  • Light-Dependent Reactions: Occur in thylakoid membranes, produce ATP and NADPH.
  • Calvin Cycle (Light-Independent Reactions): Occurs in the stroma, produces glucose.