Plant Nutrition: Leaf Structure
6.2 Leaf Structure
Adaptations Of Leaves For Photosynthesis
- Large surface area → more light absorption.
- Thin → short distance for diffusion of gases.
- Stomata → allow CO₂ in and O₂ out.
- Veins (xylem + phloem) → transport water in, sucrose out.
- Chloroplasts → absorb light energy.
Internal Leaf Structure
| Structure | Adaptation | Function |
|---|---|---|
| Cuticle | Waxy, transparent | Reduces water loss, lets light through |
| Upper epidermis | Thin, transparent | Light passes to mesophyll |
| Palisade mesophyll | Tall cells, many chloroplasts | Main site of photosynthesis |
| Spongy mesophyll | Loosely packed, air spaces | Gas exchange |
| Vascular bundle (xylem & phloem) | Xylem brings water, phloem transports sucrose | Transport system |
| Lower epidermis | Contains stomata + guard cells | Controls gas exchange |
Written And Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions And 11 World Records For Educate A Change O Level And IGCSE Biology Full Scale Course
Stomata And Guard Cells
- Stomata = pores for gas exchange.
- Guard cells open/close stomata:
- Open in light → photosynthesis.
- Close in dark/drought → prevent water loss.
Chloroplast Distribution
- Most chloroplasts in palisade cells (upper part of leaf) → best light capture.
- Fewer in spongy layer.
Key Terms
- Turgid guard cells → stomata open.
- Flaccid guard cells → stomata closed.
Written And Compiled By Sir Hunain Zia, World Record Holder With 154 Total A Grades, 7 Distinctions And 11 World Records For Educate A Change O Level And IGCSE Biology Full Scale Course