Presentation on theme: "The leaf is the main photosynthetic organ of most vascular plants Leaves - Overview Shoot system Leaf Blade Petiole Leaves generally have a flattened blade."— Presentation transcript:
The leaf is the main photosynthetic organ of most vascular plants Leaves - Overview Shoot system Leaf Blade 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
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. Palisade layer – layer where majority of chloroplasts are found ( site of photosynthesis ). 5. Spongy layer – cells surrounded by air spaces; allow water, CO 2 and O 2 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 mesophyll high photosynthesis –Spongy mesophyll air spaces for gas & water exchange Monocot leaves have 1 type of mesophyll
Leaves – Structure and Development Leaves are several layers thick – each with different cell types
Epidermis Leaves Leaf epidermis contains stomata - allow CO 2 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 Cuticle Lower epidermis Spongy mesophyll Palisade mesophyll Upper epidermis Guard cells Stomatal pore Surface view of a spiderwort (Tradescantia) leaf (LM) Epidermal cell (b) 50 µm 100 µm VeinAir spacesGuard cells Cross section of a lilac (Syringa)) leaf (LM) (c)
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.
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