1. What is Photosynthesis?
In brief:Photosynthesis is the process by which green plants make food by converting CO₂ and water to glucose and oxygen using light energy.
Photosynthesis is the process by which green plants make their own food by converting carbon dioxide and water into glucose and oxygen, using energy from sunlight.
Equation
Word equation: Carbon dioxide + Water → (light, chlorophyll) → Glucose + Oxygen
Chemical equation: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Requirements and Products
| Requirement | Source |
|---|---|
| CO₂ | Air - enters through stomata |
| Water | Soil - absorbed by roots, transported via xylem |
| Chlorophyll | Green pigment in chloroplasts |
| Light | Sun |
| Product | Destination |
|---|---|
| Glucose | Transported by phloem or stored as starch |
| Oxygen | Released through stomata; used in respiration |
Leaf Adaptations
- Large surface area - absorbs more light
- Thin - short diffusion distance for CO₂
- Chloroplasts in palisade mesophyll - maximum light absorption
- Stomata on undersurface - gas exchange
- Network of veins - transport water (xylem) and glucose (phloem)
Two Stages of Photosynthesis
Light stage (thylakoid membranes): Light energy splits water → O₂ + H⁺ + e⁻. Energy produces ATP. Electrons energised along electron transport chain.
Dark stage (stroma): CO₂ combines with H⁺ and e⁻ from the light stage, using ATP energy, to form glucose.
Photosynthesis - inputs (CO₂, H₂O, light) and outputs (glucose, O₂)
Wikimedia Commons (public domain / CC)
Chloroplast - thylakoids (light stage) and stroma (dark stage)
Wikimedia Commons (public domain / CC)
Leaf cross-section - palisade mesophyll, stomata, xylem and phloem
Wikimedia Commons (public domain / CC)
Key Points
- 1Photosynthesis: 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (requires light + chlorophyll)
- 2Occurs in chloroplasts - chlorophyll absorbs light energy
- 3Light stage: water split into O₂, H⁺, and electrons; ATP produced
- 4Dark stage: CO₂ fixed into glucose using ATP and H⁺ from light stage
- 5Leaves adapted: large surface area, thin, stomata, chloroplasts, veins
Learning Outcomes
- Outline the processes of anaerobic respiration, aerobic respiration and photosynthesis
- Investigate factors affecting the rate of photosynthesis, use primary and secondary data to support conclusions
- Model the two-stage processes of photosynthesis and respiration; make particular reference to the role of transfer molecules
- Recognise the significance of the internal structures of mitochondria and chloroplasts in facilitating the processes of photosynthesis and respiration