Overview
Summary notes for GROUP 1’s presentation: Understanding Photosynthesis from Light Reactions to the Calvin Cycle. Focus on stages, location, inputs, outputs, and key molecules.
Photosynthesis Basics
- Photosynthesis converts light energy into chemical energy stored in glucose.
- Occurs in chloroplasts, using two linked stages: light reactions and the Calvin cycle.
Light Reactions
- Location: thylakoid membranes of chloroplasts.
- Purpose: capture light to produce ATP and NADPH; release O2 from H2O.
- Inputs: light, water (H2O), ADP + Pi, NADP+.
- Outputs: oxygen (O2), ATP, NADPH.
- Core steps:
- Photosystem II absorbs light; water splits, releasing O2 and electrons.
- Electron transport chain pumps H+ to build proton gradient.
- ATP synthase uses gradient to synthesize ATP (photophosphorylation).
- Photosystem I re-energizes electrons to reduce NADP+ to NADPH.
Calvin Cycle (Light-Independent Reactions)
- Location: stroma of chloroplasts.
- Purpose: fix CO2 into carbohydrates using ATP and NADPH.
- Inputs: CO2, ATP, NADPH.
- Outputs: G3P (sugar precursor), ADP + Pi, NADP+.
- Phases:
- Carbon fixation: CO2 attaches to RuBP via RuBisCO.
- Reduction: 3-PGA reduced to G3P using ATP and NADPH.
- Regeneration: G3P used to regenerate RuBP; cycle continues.
Relationship Between Stages
- Light reactions supply ATP and NADPH required by the Calvin cycle.
- Calvin cycle returns ADP, Pi, and NADP+ to sustain light reactions.
Key Molecules and Structures
- Chlorophyll: pigment absorbing light for photosystems.
- RuBisCO: enzyme catalyzing CO2 fixation to RuBP.
- Thylakoid: site of electron transport and ATP formation.
- Stroma: fluid matrix where the Calvin cycle occurs.
- G3P: three-carbon sugar output that forms glucose and other carbohydrates.
Overall Inputs and Outputs
- Overall equation (conceptual): CO2 + H2O + light → carbohydrates + O2.
- Energy carriers cycle: NADP+/NADPH and ADP/ATP shuttle energy and electrons.
Summary Table of Stages
| Stage | Location | Main Inputs | Main Outputs | Primary Purpose |
|---|
| Light Reactions | Thylakoid membranes | Light, H2O, ADP + Pi, NADP+ | O2, ATP, NADPH | Convert light to chemical energy (ATP, NADPH) |
| Calvin Cycle | Stroma | CO2, ATP, NADPH | G3P, ADP + Pi, NADP+ | Fix carbon to synthesize sugars |
Key Terms & Definitions
- Photosystem II (PSII): complex initiating water splitting and electron flow.
- Photosystem I (PSI): complex producing NADPH from high-energy electrons.
- Photophosphorylation: ATP generation driven by light-created proton gradient.
- Carbon fixation: incorporation of CO2 into organic molecules.
- RuBP: five-carbon acceptor molecule for CO2 in the Calvin cycle.
Action Items / Next Steps
- Review electron flow from PSII to PSI and ATP/NADPH roles.
- Practice labeling chloroplast structures: thylakoid, grana, stroma.
- Memorize inputs/outputs for each stage and the linkage between them.