Chapter 29.4
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Transcript Chapter 29.4
A Closer Look at Leaves
AP Biology
Spring 2011
Leaf Structure and Function
Variation in leaf types:
Eudicot leaves:
Simple: undivided, many lobed
Compound: blades divided as leaflets
Thin, flat blade, which is attached to the stem by means
of a stalk, or petiole
Leaf Structure and Function
Monocot leaves:
Flat blades, the base of which forms a sheath around the
stem
Leaf Structure and Function
Evergreens: pants that maintain their leaves
throughout the year
Deciduous plants: lose their leaves as winter
approaches
Leaf Structure and Function
Leaves are adapted to local environmental conditions
Most plants orient their leaves perpendicular to the
suns rays to collect energy for photosynthesis
Plants growing in hot and dry regions orient their
leaves parallel with the suns rays to conserve water and
reduce heat absorption
Leaf Fine Structure
Epidermis: covers all leaf surfaces
May be smooth or covered with hairs, scales, or other
specializations
Has small openings or stomata which allow for gas
exchange
Waxy cuticle covers epidermis to minimize water loss
Leaf Fine Structure
Mesophyll: photosynthetic parenchyma
Photosynthetic parenchyma cells (in mesophyll layer)
are located between the extensive surface areas of the
upper and lower epidermis
Leaf Fine Structure
Mesophyll:
CO2 enters through stomata and diffuses through air
spaces into the photosynthetic tissue
O2 byproduct is released from the plant
Leaf Fine Structure
Mesophyll:
Dicots have two layers of mesophyll
The columnar and spongy parenchyma
Monocots are not divided into two layers
Single layer
Veins
Veins: the leafs vascular bundles
Form a network for water, solutes, and photosynthetic
products
Eudicots: large veins branch into smaller one
embedded in the mesophyll
Monocots: veins are similar in length and run parallel
with the leafs long axis