Photosynthesis Summary

Photosynthesis Overview

• Biological systems utilize energy and molecular building blocks for growth, reproduction, and homeostasis.
• Photosynthesis: process of converting CO₂, H₂O, and light energy into carbohydrates and O₂.

Evolution and Importance

• First evolved in prokaryotic organisms (cyanobacteria).
• Cyanobacterial photosynthesis contributed to an oxygenated atmosphere.
• Foundation of eukaryotic photosynthesis built on prokaryotic pathways.

Chloroplast Structure

• Stroma: fluid within the chloroplast, site of the Calvin cycle reactions.
• Thylakoids: membranes containing chlorophyll and electron transport proteins, organized into stacks called grana; site of light reactions.

Light Reactions

• Capture energy from light to produce ATP and NADPH.
• Electrons are transported through an electron transport chain (ETC) in the thylakoid membranes.
• Photosystems I and II boost electrons to a higher energy level and are linked by the ETC.

Proton Gradient and ATP Synthesis

• Electrochemical gradient of protons (H⁺) created across the thylakoid membrane.
• ATP synthase uses the proton gradient to synthesize ATP from ADP and inorganic phosphate via chemiosmosis (photophosphorylation).

Calvin Cycle

• Utilizes ATP and NADPH produced in light reactions to convert CO₂ into carbohydrates, occurring in the stroma of chloroplasts.