Photosynthesis Overview

• Photosynthesis is the process plants, some bacteria, and protistans use to convert sunlight into glucose from carbon dioxide and water.

• Products include glucose and oxygen.

• Simplified equation: CO2 + H2O → Glucose + O2.

Role of Chlorophyll

• Chlorophyll is essential for capturing sunlight; it comes in various forms but all photosynthetic organisms possess chlorophyll a.

• Accessory pigments (chlorophyll b, xanthophylls, carotenoids) absorb various wavelengths of light.

• Chlorophyll structure includes:

  • Lipid-soluble hydrocarbon tail.

  • Hydrophilic head with magnesium ion.

Leaf Structure and Function

• Leaves serve as solar collectors for photosynthetic cells.

• Water enters through roots and travels via xylem to leaves.

• Stomata allow gas exchange (CO2 in, O2 out) while minimizing water loss.

• Example: Cottonwood trees lose significant water daily.

Chloroplast Structure

• Thylakoids are the key structural units of chloroplasts; they stack to form grana, surrounded by stroma.

• Chloroplasts have three membranes, differing from mitochondria.

Stages of Photosynthesis

Light-Dependent Reactions

• Occur in thylakoid membranes:

  • Light energy excites electrons in chlorophyll.

  • Water is split (photolysis), producing O2, H+, electrons.

  • ATP and NADPH generated for light-independent reactions.

Light-Independent Reactions (Calvin Cycle)

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

• Initial products are G3P and RuBP, forming glucose and other biomolecules.

Photophosphorylation Process

• Involves two types of photosystems:

  • Photosystem II (PSII) - absorbs light for water splitting.

  • Photosystem I (PSI) - produces NADPH.

• Electron transfer described as the Z scheme, aiding ATP production.

Factors Affecting Photosynthesis

• Major factors include:

  • Light intensity - higher intensity increases rates until other factors limit.

  • CO2 concentration - more CO2 increases the light-independent reaction rate.

  • Temperature - enzyme activity affects reaction rates, peaking at optimal levels.