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Chapter 32
Leaf Structure and Function
Foliage leaves vary greatly in external form
- Leaves are so different that specific terms are used to describe their:
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Most leaves have the following:
- Blade –
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Petiole –
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Stipules –
Simple leaves have a single blade; compound leaves have multiple blades called leaflets
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Lateral buds –
Leaf Arrangements:
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Alternate –
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Opposite –
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Whorled –
Venation:
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Parallel
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Netted
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Palmate –
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Pinnate –
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The leaf consists of an epidermis, ground tissue that is photosynthetic, and vascular
tissue
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epidermis –
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cuticle –
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trichomes are commonly known as ‘leaf hairs’
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functions:
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a
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b
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c
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d
Stomata –
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Guard cells-
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Subsidaray cells-
Mesophyll is the tissue between the epidermal layers
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Mesophyll is parenchyma
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Palisade-
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Spongy2
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Veins (vascular bundles) carries the xylem and phloem throughout the mesophyll
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Xylem and phloem arrangement
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Vascular bundles are surrounded by
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Bundle sheath extensions
Leaf structure differences between monocots and dicots
Monocots
Dicots
Leaf structure is related to function
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Everything about a leaf is adapted to maximize photosynthesis and reduce water loss
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2
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3
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The leaves of each type of plant help it survive its environment
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Hydrophyllic
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Xerophyllic
Stomatal openings and closings are due to changes in guard cell turgidity
- Stomata must be open for photosynthesis to occur (except in
)
1.
2.
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Stomata open and close in response to the movement of H+ and K+ across guard cell
membranes
1.
2.
3.
Leaves lose water by transpiration and guttation
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Almost all of the water that a plant absorbs is ultimately lost by evaporation
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water loss
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transpiration
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temporary wilting
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permanent wilting
Some plants exude water
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guttation
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Leaf abscission allows plant in temperate climates to survive an unfavorable season
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All trees shed leaves
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Conifers tend to lose leave constantly
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Many Angiosperm trees abscise in the fall in preparation for winter
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Leaf Abscission
Abscission zone
Modified leaves may have varied function
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Some leaves are formed into spines for defense against herbivores
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tendrils
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bud scales
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bulbs
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succulent leaves
Modified leaves of insectivorous plants capture insects
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environment found
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how they function
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examples
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