Introduction to Photosynthesis
Definition
- Photosynthesis: A process that uses light energy to build carbohydrates (e.g., glucose).
- "Photo" means light.
- "Synthesis" means to build.
- Equation: 6 CO2 + 6 H2O + light → C6H12O6 + 6 O2
- Reactants: Water and carbon dioxide.
- Products: Glucose and oxygen.
Process Overview
- Water enters plants through roots.
- Carbon dioxide enters through stomata in leaves.
- Oxygen is released through stomata.
Organelles Involved
- Chloroplasts: Site of photosynthesis.
- Thylakoids: Contain chlorophyll, the pigment that absorbs light.
- Grana: Stacks of thylakoids.
- Stroma: Fluid inside the chloroplast.
- Mitochondria: Site of cellular respiration, the opposite of photosynthesis.
Chlorophyll
- Absorbs blue and red light, reflects green light.
- Found in thylakoids.
Stages of Photosynthesis
-
Light-Dependent Reactions
- Occur in thylakoids.
- Use water and light to produce oxygen, ATP, and NADPH.
- Photosystem II initiates the process by oxidizing water.
- Electron transport chain transfers electrons, creating a proton gradient used to produce ATP.
- NADP+ is reduced to NADPH.
-
Light-Independent Reactions (Calvin Cycle)
- Occur in the stroma.
- Use ATP, NADPH, and CO2 to produce glucose.
- Three Phases:
- Carbon Fixation: CO2 combines with ribulose biphosphate (RuBP) catalyzed by Rubisco.
- Reduction: Produces glyceraldehyde 3-phosphate (G3P), consuming ATP and NADPH.
- Regeneration: RuBP is regenerated, enabling the cycle to continue.
Photosystems and Electron Transport
- Photosystem II: Absorbs light at 680 nm.
- Photosystem I: Absorbs light at 700 nm.
- Electron carriers: Plastoquinone, Cytochrome b6f, Plastocyanin, Ferredoxin.
- ATP Synthase: Produces ATP through chemiosmosis.
Calvin Cycle Details
- Converts 3 CO2 to 1 G3P using 9 ATP and 6 NADPH.
- For 1 glucose molecule, 6 CO2 are needed, doubling the ATP and NADPH requirements.
Summary
- Photosynthesis: Light-dependent reactions occur in thylakoids, and the Calvin cycle occurs in stroma.
- Key products: Glucose, oxygen, ATP, NADPH.
This concludes the summary of photosynthesis. It covers the essential components and stages involved in the process.