Overview
This lecture covers the process of photosynthesis in plants, its importance, main steps, and plant adaptations for efficient photosynthesis.
Importance of Photosynthesis
- Photosynthesis enables plants to make their own food (glucose) from sunlight.
- This process also produces oxygen, which animals, including humans, need to survive.
- Plants are primary producers in food webs and essential for food and medicine.
Photosynthesis Equation & Relationship to Respiration
- The overall equation for photosynthesis is:
6 CO₂ + 6 H₂O + light energy → C₆H₁₂O₆ + 6 O₂
- Photosynthesis inputs are the outputs of cellular respiration and vice versa.
- Both plants and animals use glucose for cellular respiration, but plants make their own.
Pigments and Light Absorption
- Plants use pigments, mainly chlorophyll, to capture light energy.
- Chlorophyll absorbs red and blue light, but reflects green, making many plants appear green.
- Other pigments allow plants to use a wider range of light wavelengths.
Photosynthesis Process: Two Major Reaction Sets
- Photosynthesis occurs in chloroplasts, which contain thylakoids (site of light-dependent reactions) and stroma (site of light-independent reactions).
Light-Dependent Reactions
- Take place in thylakoids; thylakoid stacks are called grana.
- Capture light energy to split water into electrons, protons, and oxygen (O₂ is released).
- Produce ATP and NADPH for the next stage.
Light-Independent Reactions (Calvin Cycle)
- Occur in the stroma of the chloroplast.
- Use ATP and NADPH from light-dependent reactions and CO₂ from the air.
- Carbon dioxide enters through stomata (leaf pores) and is fixed into organic molecules.
- The end product is glucose.
Plant Adaptations for Photosynthesis
- Plants have diverse leaf shapes, coverings, and pigments to maximize photosynthesis in different environments.
- Cacti use CAM photosynthesis: open stomata at night to collect and store CO₂, reducing water loss during hot days.
Key Terms & Definitions
- Photosynthesis — Process by which plants use sunlight to make glucose and oxygen from carbon dioxide and water.
- Chlorophyll — Green pigment in plants that absorbs light for photosynthesis.
- Chloroplast — Organelle where photosynthesis takes place.
- Thylakoid — Membrane structure in chloroplasts where light-dependent reactions occur.
- Stroma — Fluid in chloroplasts where Calvin Cycle occurs.
- Stomata — Pores on leaves for gas exchange.
- CAM Photosynthesis — Adaptation allowing plants to fix CO₂ at night to conserve water.
Action Items / Next Steps
- Review further reading links mentioned for more detail on photosystems and Calvin Cycle steps.
- Explore adaptations of photosynthesis in various environments.