Overview
This lecture explains the process of photosynthesis in plants, its importance, and key adaptations for efficiency, including basic reactions and special cases like CAM photosynthesis.
Photosynthesis: Purpose and Significance
- Photosynthesis is the process by which plants make their own glucose (sugar) using sunlight.
- This process also produces oxygen, which is essential for animal and human respiration.
- Plants are primary producers in food webs and are vital for food and medicine.
Photosynthesis Overview and Equation
- The overall equation for photosynthesis: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂.
- Photosynthesis reactants are CO₂, H₂O, and light; products are glucose and O₂.
- Photosynthesis and cellular respiration have interconnected inputs and outputs but are not exact reverse reactions.
Pigments and Light Capture
- Plants capture light using pigments, mainly chlorophyll, located in chloroplasts.
- Chlorophyll absorbs red and blue light but reflects green, making plants appear green.
- Other pigments absorb other light wavelengths, giving variety in plant colors.
Two Main Stages of Photosynthesis
- Photosynthesis includes light-dependent reactions and light-independent reactions (Calvin Cycle).
- Light-dependent reactions occur in thylakoids (inside chloroplasts) and require light.
- These reactions split water, releasing oxygen and producing ATP and NADPH.
- Light-independent reactions (Calvin Cycle) occur in the stroma of the chloroplast.
- The Calvin Cycle uses ATP, NADPH, and CO₂ to produce glucose.
Gas Exchange and Stomata
- Carbon dioxide enters plant leaves through pores called stomata.
- Stomata can open and close to regulate gas exchange and water loss.
Plant Adaptations in Photosynthesis
- Plants have diverse adaptations (leaf shapes, pigments) for photosynthesis in various environments.
- Cacti use CAM photosynthesis, opening stomata at night to reduce water loss in hot climates.
Key Terms & Definitions
- Photosynthesis — the process by which plants convert light energy, CO₂, and water into glucose and oxygen.
- Chlorophyll — a pigment in chloroplasts that absorbs light for photosynthesis.
- Chloroplast — organelle in plant cells where photosynthesis occurs.
- Thylakoid — membrane-bound compartment inside chloroplasts, site of light-dependent reactions.
- Stroma — fluid area of the chloroplast outside thylakoids, site of the Calvin Cycle.
- Stomata — pores on leaves for gas exchange.
- Calvin Cycle — series of light-independent reactions that produce glucose from CO₂.
- CAM Photosynthesis — adaptation allowing plants to fix CO₂ at night to conserve water.
Action Items / Next Steps
- Review the chemical equation for photosynthesis.
- Explore further reading on photosystems, Calvin Cycle steps, and adaptations.
- Study how ATP and NADPH cycle between the two reaction stages.