Overview
This lecture introduces photosynthesis, covering its definition, importance to life on Earth, chemical equation, plant cell structures involved, and the role of pigments, water, light, and carbon dioxide in the process.
What Makes Plants Unique
- Plants are unique because they can make their own food through photosynthesis.
- Photosynthesis is essential to all life on Earth, as it begins the food chain and provides oxygen.
Importance of Photosynthesis in Ecosystems
- Plants and plant-like organisms (like phytoplankton) are the base of food webs in both terrestrial and aquatic environments.
- Removing plants would collapse food webs, affecting all organisms, including carnivores.
- Photosynthesis provides oxygen as a byproduct, essential for most life forms.
Definition and Equation of Photosynthesis
- Photosynthesis means "putting together with light."
- The process uses carbon dioxide and water, along with sunlight, to produce glucose and oxygen.
- Chemical equation: 6CO₂ + 6H₂O + sunlight → C₆H₁₂O₆ + 6O₂.
- Photosynthesis is an autotrophic process, allowing organisms to make their own food.
Structures Involved in Photosynthesis
- Main organ for photosynthesis is the leaf, with other green plant parts also able to photosynthesize.
- Photosynthesis occurs in chloroplasts within leaf cells.
- Key parts of leaf: cuticle (waxy layer), epidermis (protective layers), mesophyll (site of photosynthesis), stomata (gas exchange), vascular bundles (xylem transports water; phloem transports food).
Chloroplasts and Pigments
- Chloroplasts contain chlorophyll, a pigment that absorbs all visible light except green, which is reflected.
- Other pigments include anthocyanins (reflect red) and carotenoids (reflect yellow/orange).
- Chloroplast structure: outer and inner membrane, thylakoid (disk), granum (stack), stroma (fluid), lumen (inside thylakoid).
- Wild-type plants have 80–100 chloroplasts per mesophyll cell.
Role of Light and Pigments
- Light is absorbed as photons by pigments, mainly chlorophyll, to drive photosynthesis.
- Chlorophyll absorbs blue and red wavelengths but reflects green.
- During fall, chlorophyll breaks down, revealing other pigments and changing leaf color.
Key Terms & Definitions
- Photosynthesis — Process where plants use light, CO₂, and water to produce glucose and oxygen.
- Autotrophic — Self-feeding; organisms that produce their own food.
- Chloroplast — Organelle where photosynthesis occurs in plant cells.
- Chlorophyll — Green pigment that absorbs light for photosynthesis.
- Stomata — Small openings on leaves for gas exchange.
- Mesophyll — Leaf tissue where most photosynthesis occurs.
- Xylem — Vascular tissue transporting water.
- Phloem — Vascular tissue transporting food.
- Thylakoid — Flattened sac inside chloroplasts, site of the light-dependent reactions.
- Granum (Grana) — Stack(s) of thylakoids.
Action Items / Next Steps
- Review parts of the leaf and chloroplast.
- Prepare for next lecture on the light-dependent and light-independent reactions of photosynthesis.