1. Leaves - Overview
Shoot
system
Leaf
Blade
Petiole
The leaf is the main photosynthetic organ of most vascular plants
Leaves generally have a flattened blade and a stalk called the petiole,
which joins the leaf to a node of the stem

2. Leaves - Comparisons
Monocots and Dicots differ in the arrangement of veins, the vascular tissue of leaves
Most Dicots have branch-like veins and palmate leaf shape
Monocots have parallel leaf veins and longer, slender blades

3. Leaf Parts
1. Stoma (stomata) – small pores that act as a doorway for gases involved in photosynthesis (found mainly on the underside of leaves). 2. Guard Cells – Cells that regulate the opening of the stomata. 3. Lower and upper epidermis – outer layer of a plant that serves for protection, like skin.

4. Leaf parts continued…
4. Palisade layer – layer where majority of chloroplasts are found (site of photosynthesis). 5. Spongy layer – cells surrounded by air spaces; allow water, CO2 and O2 to diffuse during photosynthesis. 6. Waxy layer/cuticle – protects leaf from water loss and from feeding insects.

5. Leaves – Structure and Development
Most dicots have 2 types of mesophyll
Palisade mesophyll
high photosynthesis
Spongy mesophyll
air spaces for gas & water exchange
Monocot leaves have 1 type of mesophyll

6. Cross Section of a Leaf

7. Leaves – Structure and Development
Leaves are several layers thick – each with different cell types

8. Epidermis Leaves Leaf epidermis contains stomata - allow CO2 exchange
Stomata flanked by two guard cells, control open vs. closed
The ground tissue in a leaf, called mesophyll, fills the middle
Key
to labels
Dermal
Ground
Vascular
Cuticle
Sclerenchyma
fibers
Stoma
Bundle-
sheath
cell
Xylem
Phloem
(a) Cutaway drawing of leaf tissues
Guard
cells
Vein
Lower
epidermis
Spongy
mesophyll
Palisade
Upper
Stomatal
pore
Surface view of a spiderwort
(Tradescantia) leaf (LM)
Epidermal
(b)
50 µm
100 µm
Air spaces
Guard cells
Cross section of a lilac
(Syringa)) leaf (LM)
(c)
Figure Organization of primary tissues in young stems

9. Vascular Tissue
Xylem – cells that carry water and dissolved minerals from the roots to the leaves.
Phloem – cells that carry food (sugar) that is made in the leaves to all parts of the plant.
Use: Collectively the vascular tissue, xylem and phloem create a vein or vascular bundle to transport material in plants.

10. Stoma Open vs. Closed
Open – with light and when guard cells are filled with water.
Closed – without light and when guard cells are lacking water (dehydrated).
Why is it important to have stomata open?
Closed vs. Open

25. Question time????????