Photosynthesis Notes

Photosynthesis

Overview

• Photosynthesis Equation: (To be written on the next Monday unit test)

Chloroplasts and Photosynthesis

• Chloroplasts in leaf cells use chlorophyll to absorb light energy for food molecule production.
  • Chloroplasts are concentrated in the mesophyll inside a leaf.
• CO2 enters, and O2 exits through stomata.
• Chloroplast structure:
  • Inner and outer membranes.
  • Stroma: thick fluid where glucose is stored.
  • Thylakoids: membranous sacs in stacks (grana).
  • Photosynthesis occurs in thylakoid membranes.

Photosynthesis Stages

• Two stages linked by ATP and NADPH:
  • Light reaction:
    • Light energy converted to chemical bond energy; O2 released.
  • Calvin-Benson cycle (Dark Phase):
    • Occurs in stroma, does not require light
    • Assembles glucose using CO2 and products from the light reaction.
• Light energy converts ADP to ATP and NADP+ to NADPH (using electrons and H+ from water).

Chlorophyll and Light Absorption

• Chlorophyll types:
  • Chlorophyll a: Absorbs blue-violet and red light.
  • Chlorophyll b: Absorbs blue and orange light.
• Light excites chlorophyll electrons, passed to primary electron acceptor.
• Chlorophyll a, chlorophyll b, and carotenoid pigments are located in thylakoid membranes.

Light Reactions

• Generate ATP, NADPH, and O2.
• Key events:
  • Light energy absorption.
  • Electron excitation.
  • ATP and NADPH formation.

Photosystems

• Photosystem I:
  • Primary electron acceptor donates electrons stored in NADPH.
• Photosystem II:
  • Gets electrons from water, produces ATP.
• NADPH, ATP, and O2 are products of the light reactions.

Calvin Cycle

• ATP and NADPH power sugar synthesis.
• Inputs: CO2, ATP, and NADPH.
• Product: glyceraldehyde-3-phosphate (G3P), a building block for organic molecules.