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The leaf is the main photosynthetic organ of most vascular plants Leaves - Overview Shoot system Leaf Blade Petiole Leaves generally have a flattened blade

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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 Slide 2 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 Slide 3 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. Slide 4 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. Slide 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 Slide 6 Slide 7 Leaves Structure and Development Leaves are several layers thick each with different cell types Slide 8 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 m 100 m VeinAir spacesGuard cells Cross section of a lilac (Syringa)) leaf (LM) (c) Slide 9 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. Slide 10 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 Slide 11 Slide 12 Slide 13 Slide 14 Slide 15 Slide 16 Slide 17 Slide 18 Slide 19 Slide 20 Slide 21 Slide 22 Slide 23 Slide 24 Slide 25 Question time???????? Slide 26

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