Chapter 29.4

1. Chapter 29.4 A Closer Look at Leaves AP Biology Spring 2011

2. 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

3. Leaf Structure and Function • Monocot leaves: • Flat blades, the base of which forms a sheath around the stem

4. Leaf Structure and Function • Evergreens: pants that maintain their leaves throughout the year • Deciduous plants: lose their leaves as winter approaches

5. 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

6. 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

7. 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

8. Leaf Fine Structure • Mesophyll: • CO2 enters through stomata and diffuses through air spaces into the photosynthetic tissue • O2 byproduct is released from the plant

9. Leaf Fine Structure • Mesophyll: • Dicots have two layers of mesophyll • The columnar and spongy parenchyma • Monocots are not divided into two layers • Single layer

10. 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