Biology
Form II
BIO-F2-05
✓ Verified TIE Syllabus
Gaseous Exchange in Plants
Mechanisms of gas exchange in vegetative plant organs: stomatal mechanics, lenticel diffusion, respiration versus photosynthesis gas exchange, and environmental adaptations.
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🎯 Syllabus Competencies & Learning Objectives
Key Competencies
- Main: 1.0 Demonstrate mastery of the concepts, principles and processes of Biology
- Specific: 1.1 Describe the physiological, anatomical and ecological processes of living organisms
Specific Learning Objectives
- Identify plant structures responsible for gaseous exchange (stomata, lenticels, root hairs).
- Explain the mechanism of opening and closing of stomata using turgor pressure and potassium ion theories.
- Compare daytime versus nighttime gaseous exchange in green leaves.
📖 Comprehensive Study Notes Summary
### Gaseous Exchange in Plants
Unlike mammals, plants lack specialized circulatory and respiratory pumping systems. Gas exchange occurs by simple diffusion through:
1. **Stomata**: Chiefly located on the lower epidermis of leaves.
2. **Lenticels**: Loosely packed cork cells in woody stems.
3. **Root Epidermis / Hairs**: Direct diffusion from soil air spaces.
#### Mechanism of Stomatal Action
- Guard cells have thick inner cellulose walls and thin outer walls.
- In light: Guard cells actively accumulate K+ ions -> osmotic potential drops -> water enters by osmosis -> guard cells become turgid, bowing outward and opening the stoma.
- In darkness: K+ ions diffuse out -> water leaves guard cells -> guard cells become flaccid, closing the stoma pore.
Unlike mammals, plants lack specialized circulatory and respiratory pumping systems. Gas exchange occurs by simple diffusion through:
1. **Stomata**: Chiefly located on the lower epidermis of leaves.
2. **Lenticels**: Loosely packed cork cells in woody stems.
3. **Root Epidermis / Hairs**: Direct diffusion from soil air spaces.
#### Mechanism of Stomatal Action
- Guard cells have thick inner cellulose walls and thin outer walls.
- In light: Guard cells actively accumulate K+ ions -> osmotic potential drops -> water enters by osmosis -> guard cells become turgid, bowing outward and opening the stoma.
- In darkness: K+ ions diffuse out -> water leaves guard cells -> guard cells become flaccid, closing the stoma pore.