Photosynthesis Flashcards

Photosynthesis Stages

Light Reactions

  • Occur in the thylakoid membranes.

  • Convert light energy to chemical energy (ATP and NADPH).

  • Primary Events:

    • Light energy absorbed, drives e^- transfer from water to NADP+, forming NADPH.

    • Water is split, O_2 released.

    • ATP generated via chemiosmosis (photophosphorylation).

Calvin Cycle

  • Occurs in the stroma.

  • CO_2 incorporated into organic molecules (carbon fixation).

  • Uses fixed carbon, NADPH, and ATP from light reactions to form sugars.

Chloroplast Structure

  • Stroma: Fluid-filled area enclosed by two membranes.

  • Thylakoids: Interconnected membranous sacs within the stroma, segregating the thylakoid space.

  • Chlorophyll: Located in thylakoid membranes, absorbs light.

Overall Photosynthesis Reaction

  • 6CO2 + 6H2O + Light Energy \rightarrow C6H{12}O6 + 6O2

  • Reverse of cellular respiration.

  • Oxygen produced from splitting water molecules.

Photosystems

  • Located in the thylakoid membrane.

  • Consist of a light-harvesting complex and a reaction center.

  • Light-harvesting complex: Chlorophyll and carotenoid molecules that gather light.

Chemiosmosis

  • Electron transport chain pumps protons across the thylakoid membrane, creating an electrochemical gradient.

  • ATP synthase uses the proton gradient to phosphorylate ADP to ATP.

  • Proton-motive force generated by:

    • Hydrogen ions from water splitting.

    • Hydrogen ions pumped across the membrane.

    • Removal of hydrogen ions from the stroma during NADPH production.

Calvin Cycle Steps

  1. 3CO_2 attach to 3 RuBP (ribulose bisphosphate) catalyzed by rubisco, forming unstable product that splits into 6 molecules of 3-phosphoglycerate.

  2. 3-phosphoglycerate phosphorylated (using ATP) to become 1,3-bisphosphoglycerate.

  3. 1,3-bisphosphoglycerate reduced by 6 NADPH to 6 glyceraldehyde-3-phosphate (G3P).

  4. One G3P leaves to form glucose.

  5. Remaining 5 G3P rearranged to regenerate 3 RuBP.

Adaptations to Arid Climates

  • C4 and CAM photosynthesis are adaptations to reduce photorespiration in hot, arid conditions.

  • C3 plants close stomata to conserve water, leading to reduced CO_2 uptake and less sugar production.