Photosynthesis Overview

• Process by which plants, bacteria, and protistans convert sunlight into glucose from CO₂ and H₂O.

• Summarized equation: CO₂ + H₂O → Glucose + O₂

• Chlorophyll is essential for energy conversion; includes chlorophyll a and accessory pigments (b, c, d, e, xanthophylls, carotenoids).

Leaf Structure

• Leaves function as solar collectors; facilitate gas exchange (CO₂ in, O₂ out).

• Water is absorbed by roots and transported via xylem to leaves.

• Stomata control gas exchange and minimize water loss.

Chloroplast Structure

• Thylakoids are the sites of photosynthesis, organized in stacks (grana) within chloroplasts, which have three membrane compartments.

Stages of Photosynthesis

Light-dependent Reactions

• Occur in thylakoids; require light energy.

• Chlorophyll absorbs light, excites electrons (photoexcitation), leading to water splitting (photolysis).

• Produce ATP (via photophosphorylation) and NADPH from NADP+.

Light-independent Reactions (Calvin Cycle)

• Occur in stroma; utilize ATP and NADPH to fix CO₂ into carbohydrates.

• Form intermediates like glyceraldehyde 3-phosphate (GALP).

Non-Cyclic and Cyclic Phosphorylation

• Non-Cyclic: Produces both ATP and NADPH using PSII and PSI.

• Cyclic: Generates extra ATP from PSI without NADPH, assisted by electron transport chain.

Chemiosmosis

• ATP synthesis driven by H+ diffusion across thylakoid membrane, creating an electrochemical gradient.

Factors Affecting Photosynthesis

• Limiting factors: Light intensity, CO₂ concentration, temperature.

• Optimal light wavelength crucial (PSI: 700 nm; PSII: 680 nm).