Download 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