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.