Overview
This lecture explores the process of photosynthesis in plants, its significance, main steps, key molecules, and adaptations allowing plants to survive in different environments.
Photosynthesis and Its Importance
- Photosynthesis is the process by which plants make their own food, specifically glucose.
- The process also produces oxygen, which animals and humans require to survive.
- Plants are primary producers in food webs and provide many foods and medicines.
Photosynthesis Equation & Comparison to Cellular Respiration
- The overall balanced equation for photosynthesis is: 6CO₂ + 6H₂O + light energy → C₆H₁₂O₆ + 6O₂.
- Inputs of photosynthesis are outputs of cellular respiration and vice versa, but the processes are not simply reversed.
- Both plants and animals need glucose for cellular respiration; plants do not need to ingest glucose since they make it.
Pigments and Light Capture
- Plants use pigments, especially chlorophyll, to capture light energy from the sun.
- Chlorophyll absorbs red and blue light but reflects green, making plants appear green.
- Other pigments in plants allow absorption of different light wavelengths.
Structure of the Chloroplast
- Photosynthesis takes place in the chloroplast, which contains thylakoids (stacked as grana) and stroma (fluid around thylakoids).
- Pigments like chlorophyll are found within the thylakoids.
Two Main Reactions of Photosynthesis
- Light Dependent Reactions occur in thylakoids, capturing light and splitting water to produce oxygen, ATP, and NADPH.
- Light Independent Reactions (Calvin Cycle) occur in the stroma, using ATP and NADPH to fix carbon dioxide and produce glucose.
Stomata and Gas Exchange
- CO₂ enters leaves through pores called stomata, which plants can open and close to regulate gas exchange and water loss.
- An enzyme in the Calvin Cycle helps convert inorganic CO₂ into organic molecules.
Plant Adaptations in Photosynthesis
- Plants have adaptations (leaf shapes, coverings, pigments) to perform photosynthesis efficiently in diverse environments.
- Cacti use CAM photosynthesis, opening stomata at night to collect CO₂, reducing water loss during hot days.
Key Terms & Definitions
- Photosynthesis — Process by which plants convert light energy, CO₂, and water into glucose and oxygen.
- Chlorophyll — Main pigment in plants 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-filled space surrounding thylakoids in the chloroplast.
- Light Dependent Reactions — Photosynthesis stage using light to produce ATP, NADPH, and oxygen.
- Light Independent Reactions (Calvin Cycle) — Stage using ATP and NADPH to convert CO₂ into glucose.
- Stomata — Pores on leaf surfaces for gas exchange.
- CAM Photosynthesis — Adaptation allowing some plants to fix CO₂ at night to minimize water loss.
Action Items / Next Steps
- Review the photosynthesis equation and understand the role of each component.
- Explore further reading on detailed steps of the light-dependent reactions and Calvin Cycle.