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The leaf is the main photosynthetic organ of most vascular plants
Leaves - Overview
Shootsystem
LeafBlade
Petiole
Leaves generally have a flattened blade and a stalk called the petiole, which joins the leaf to a node of the stem
Most Dicots have branch-like veins and palmate leaf shape
Monocots have parallel leaf veins and longer, slender blades
Leaves - Comparisons
Monocots and Dicots differ in the arrangement of veins, the vascular tissue of leaves
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.
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.
Leaves – Structure and Development
• Most dicots have 2 types of mesophyll– Palisade
mesophyllhigh
photosynthesis– Spongy
mesophyllair spaces for gas
& water exchange
• Monocot leaves have 1 type of mesophyll
CROSS SECTION OF A LEAF
Leaves – Structure and Development
• Leaves are several layers thick – each with different cell types
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
middleKey
to labels
Dermal
Ground
VascularCuticle Sclerenchyma
fibersStoma
Bundle-sheathcell
Xylem
Phloem
(a) Cutaway drawing of leaf tissuesGuardcells
Vein
Cuticle
Lowerepidermis
Spongymesophyll
Palisademesophyll
Upperepidermis
Guardcells
Stomatalpore
Surface view of a spiderwort(Tradescantia) leaf (LM)
Epidermalcell
(b)
50 µ
m1
00
µm
Vein Air spaces Guard cells
Cross section of a lilac(Syringa)) leaf (LM)
(c)
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.
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
Question time????????