A Closer Look at Leaves

AP BiologySpring 2011

Leaf Structure and FunctionVariation in leaf types:

Eudicot leaves:Simple: undivided, many lobed Compound: blades divided as leafletsThin, flat blade, which is attached to the stem

by means of a stalk, or petiole

Leaf Structure and FunctionMonocot leaves:

Flat blades, the base of which forms a sheath around the stem

Leaf Structure and FunctionEvergreens: pants that maintain their leaves

throughout the yearDeciduous plants: lose their leaves as

winter approaches

Leaf Structure and FunctionLeaves 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 exchangeWaxy 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 mesophyllThe columnar and spongy parenchyma Monocots are not divided into two layers

Single layer

VeinsVeins: the leafs vascular bundles Form a network for water, solutes, and

photosynthetic productsEudicots: large veins branch into smaller one

embedded in the mesophyll Monocots: veins are similar in length and run

parallel with the leafs long axis