Overview
This lecture explains the internal structure of a dicotyledonous plant leaf, highlighting how its components support gas exchange and photosynthesis.
Leaf Structure
- The leaf's upper and lower surfaces are covered by upper and lower epidermis layers.
- Both epidermal layers are topped with a thin waxy cuticle to reduce water loss.
- The palisade mesophyll, beneath the upper epidermis, consists of tightly-packed, cylinder-shaped cells rich in chloroplasts for photosynthesis.
- Below the palisade mesophyll is the spongy mesophyll, made of irregular cells with many air spaces and fewer chloroplasts.
Gas Exchange
- Epidermis contains small pores called stomata, which enable gas exchange.
- Each stoma is bordered by two guard cells that open and close the pore.
- Guard cells contain chloroplasts, unlike other epidermal cells.
Vascular System
- The midrib and leaf veins, located in the mesophyll, house vascular bundles.
- Each vascular bundle consists of xylem (transports water and minerals) and phloem (transports food).
Key Terms & Definitions
- Epidermis — outer protective cell layer on leaf surfaces.
- Cuticle — waxy layer atop the epidermis that limits water loss.
- Palisade Mesophyll — layer of chloroplast-rich, column-like cells where most photosynthesis occurs.
- Spongy Mesophyll — loosely arranged cells with air spaces to facilitate gas exchange.
- Stomata — tiny pores in the epidermis for gas exchange.
- Guard Cells — specialized cells controlling stomatal opening and closing.
- Vascular Bundle — structure containing xylem and phloem for transport within the leaf.
- Xylem — tissue that carries water and minerals.
- Phloem — tissue that distributes food produced by photosynthesis.
Action Items / Next Steps
- Review the labeled diagram of a dicot leaf for each structure discussed.