1. Figure 23–18 The Internal Structure of a Leaf
Cuticle
Veins
Epidermis
Palisade mesophyll
Xylem
Vein
Phloem
Spongy mesophyll
Epidermis
Stoma
Guard cells

2. Leaf Structures & Functions
Epidermis – layer of tough, irregularly shaped cells; covered by cuticle; form waterproof barrier that protects tissues and limits water loss through evaporation
Mesophyll – photosynthesis in most plants occurs here
Palisade mesophyll – tall columnar, cells; closely packed
Spongy mesophyll – loose; many air spaces that connect to exterior through stomata

3. Stomata – porelike openings in the underside of the leaf; allows carbon dioxide and oxygen to diffuse into and out of leaf
Guard cells – control the opening and closing of stomata by responding to changes in water pressure
Plants keep their stomata open just enough to allow photosynthesis to take place but not so much that they lose an excessive amount of water
In general, stomata are open during the daytime when photosynthesis is active, and closed at night.
May be closed during hot, dry conditions to reduce water loss.

4. Vein – vascular tissue connected to vascular tissue of stems; transport system
xylem – carries water from roots to rest of plant
phloem – carries nutrients and food made by photosynthesis

5. Function of Guard Cells
Section 23-4
Guard cells
Guard cells
Inner cell wall
Inner cell wall
Stoma
Stoma Open
Stoma Closed

6. Function of Guard Cells
Section 23-4
Guard cells
Guard cells
Inner cell wall
Inner cell wall
Stoma
Stoma Open
Stoma Closed