leaf structure.ppt

leaf structure.ppt

• 1.
  Leaves: Form and structure Chapter6
• 2.
  The Plant Body:Leaves • FUNCTION OF LEAVES – Leaves convert light energy to chemical energy
• 3.
  And so, onto leaves • Leaves are the principle structure, produced on stems, where photosynthesis takes place. • Cacti are an exception. The leaves are reduced to spines, and the thick green, fleshy stems are where photosynthesis takes place.
• 4.
  General leaf form •Leaves are the main photosynthetic organs of most plants – but green stems are also photosynthetic. – While leaves vary extensively in form, they generally consist of a flattened blade and a stalk, the petiole, which joins the leaf to a stem node. • Most monocots have parallel major veins that run the length of the blade, while dicot leaves have a multi branched network of major veins. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Blade Petiole
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  • Plant taxonomistsuse leaf shape, spatial arrangement of leaves, and the pattern of veins to help identify and classify plants. – A Simple leaves have a single, undivided blade, while compound leaves have several leaflets attached to the petiole. – A Compound leaf has a bud where its petiole attaches to the stem, not at the base of the leaflets. Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings Leaf Arrangement on the Stem
• 6.
  Most dicots have branch-likeveins 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
• 7.
  Structures of the Leaf Cuticle– the outermost layer of both the upper and lower surfaces of the leaf. It is clear and waxy to prevent against water loss. Epidermis – a layer of cells one cell thick that provides protection for the inner tissues. These cells are clear to allow light to reach the photosynthetic tissues. Mesophyll – between the epidermal layers. It contains palisade cells that are tall, tightly packed, and filled with chloroplasts for photosynthesis.
• 8.
  Structures of the Leaf Stomates– openings in the surface of the leaf and stems for gas exchange. The lower surface of a leaf usually has more. Water vapor also passes out through these holes. . Veins – contain the vascular tissue that is continuous with that in the stem. Xylem carries water and minerals upward. Phloem carries dissolved food throughout the plant.
• 9.
  Stomatal control • Whenwater is abundant: • Temporal regulation of stomata is used: – OPEN during the day – CLOSED at night • At night there is no photosynthesis, so no demand for CO2 inside the leaf • Stomata closed to prevent water loss • Sunny day - demand for CO2 in leaf is high – stomata wide open • As there is plenty of water, plant trades water loss for photosynthesis products
• 10.
  Figure 11.12 (2) SpecializedLeaves • The Venus fly trap has an “active trap” • Good control over turgor pressure in each plant cell. • When the trap is sprung, ion channels open and water moves rapidly out of the cells. • Turgor drops and the leaves slam shut • Digestive enzymes take over