Leaf - form and function
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Leaves can differ greatly in shape, margin, venation and attachment Often the first thing looked at for identification Have blade, petiole and usually a stipule
Leaf structure
Leaf form
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Simple leaves have one blade Veins may be:
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netted (dicot) parallel (monocot)
Examples of: pinnately netted venation palmately netted venation
Axillary buds
“Axil” of leaf (the angle between the stem and the petiole)
Bud
Leaf arrangement
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Leaflets are found on compound leaves Buds in the axil of the leaf Pinnately compound leaves
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Palmate
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Even
leaflets opposite (odd or even #)
Bud
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Palmately compound
Odd
Three patterns of leaf
Leaf anatomy
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Cuticle Upper epidermis Palisade parenchyma Vascular bundle Spongy parenchyma Lower epidermis Stoma
Leaf x-section (photomicrograph)
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Note stomatal chamber Palisade parenchyma may be one or several layers
Leaf x-section
Note the stomata l chambe
Stomata (leaf pores)
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Ivy lower epidermis Stomata with guard cells
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Corn epidermal peel
Stoma with chamber
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An open area or chamber is found “below” (to the inside of) the stomatal opening
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Diffusion
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Materials diffuse from areas of highest to lowest concentration It is a random process
Pore diffusion
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Many small pores are more efficient at diffusion than one large pore of the same total area. Diffusion is more linked to circumference than to area
Pore diffusion
“Spill over” accounts for the perimeter effect
Leaf pores - stomata
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Guard cells can expand and open a pore between them Opening affected by light, CO2, hormones, dehydration, biological clock
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Guard cell mechanism
Closed condition Inner walls meet
Guard cell mechanism
Movement of K+ into the cells causes water movement into the cell, expanding
Leaf abscission
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Abscission zone near base of petiole
Petiole
Bud Stem
Specialized leaves
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Insectivorus plants Vines Succulents