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The leaf is the main photosynthetic organ of most vascular plants

Shoot system. Blade. Leaf. Petiole. Leaves - Overview. 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. Leaves - Comparisons.

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The leaf is the main photosynthetic organ of most vascular plants

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  1. Shoot system Blade Leaf Petiole Leaves - Overview 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 • Monocots have parallel leaf veins and longer, slender blades • Most dicots have branch-like veins and palmate leaf shape

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

  4. Leaf parts continued… • Palisade layer – layer where majority of chloroplasts are found (site of photosynthesis). • Spongy layer – cells surrounded by air spaces; allow water, CO2 and O2 to diffuse during photosynthesis. • 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. Plant Growth - Leaves Guard cells Key to labels Stomatal pore 50 µm Dermal Epidermal cell Ground Cuticle Sclerenchyma fibers Vascular Stoma (b) Surface view of a spiderwort (Tradescantia) leaf (LM) Upper epidermis Palisade mesophyll Spongy mesophyll Bundle- sheath cell Lower epidermis 100 µm Cuticle Xylem Vein Phloem Vein Air spaces Guard cells Guard cells (a) Cutaway drawing of leaf tissues (c) Cross section of a lilac (Syringa)) leaf (LM) • 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

  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. • 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

  11. Question time????????

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