4 Organs - Leaves

4 Organs - Leaves - Lecture: 4 BioSci 1C Apr.3.07 Plant...

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Lecture: 4 BioSci 1C Apr.3.07 Plant Organs, Stems and Leaves
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Functions of Leaves • Photosynthesis – Release oxygen, synthesize sugars • Transpiration – Evaporation of water from leaf surface • Specialized functions – Water storage – Protection
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Leaf Blade • Broad, flat surface for capturing light and CO 2 • Two types of leaves – Simple leaves – Compound leaves
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Leaf Blade • Simple leaves – Leaves with a single blade – Examples •Pop la r
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Fig. 6-2, p. 93 b Compound leaves midrib poplar ( Populus ) oak ( Quercus ) maple ( Acer ) blade petiole leaflets red buckeye ( Aesculus ) black locust ( Robinia ) honey locust ( Gleditsia ) a Simple leaves Palmate Pinnate
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Leaf Blade • Compound leaves – Blade divided into leaflets –Two types • Palmately compound – Leaflets diverge from a single point – Example: red buckeye • Pinnately compound – Leaflets arranged along an axis – Examples: black locust, honey locust
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Leaf Blade – Advantages of compound leaves • Spaces between leaflets allow better air flow over surface – May help cool leaf – May improve carbon dioxide uptake
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blade petiole stem sheath blade midrib parallel veins bud Dicot Monocot node node Leaf Structure
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Comparison of Monocot and Dicot Leaves Petiole holds blade away from stem Netted pattern of vascular bundles Thin, flat blade Dicot Leaf bases usually wrap around stem Parallel vascular bundles Strap-shaped *blade Monocot Description Venation Shape of blade Type *blade – portion of leaf that absorbs light energy
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Fig. 6-4a, p. 94 Venation patterns Monocot Dicot
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Petiole • Narrow base of most dicot leaves • Leaf without petiole – sessile • Vary in shape • Improves photosynthesis – Reduces extent to which leaf is shaded by other leaves – Allows blade to move in response to air currents
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Sheath • Formed by monocot leaf base wrapping around stem • Ligule – Keeps water and dirt from getting between stem and leaf sheath • Auricles – In some grass species – Two flaps of leaf tissue – Extend around stem at juncture of sheath and blade
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Fig. 6-3a, p. 93 Crabgrass node blade stem sheath
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Fig. 6-3b, p. 93 node ligule sheath Corn In corn the sheath extends Almost the entire length of the internodes, there is even a small flap of tissue, a ligule, extending upward from the sheath.
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Fig. 6-3c, p. 93 Barley stem sheath blade auricles ligule
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4 Organs - Leaves - Lecture: 4 BioSci 1C Apr.3.07 Plant...

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