1. Leaves
leaves are the primary site of photosynthesis and gas exchange in most plant species

2. Structure of Leaves most leaves have a flattened area called a blade
blade is attached to the stem by a stalk-like structure called a petiole
leaves can be simple, with just one blade, or compound, with several leaflets

3. Structure of Leaves Cont’d…
veins of leaves contain the vascular tissue
arrangement of the veins within a leaf is called its venation
monocots have parallel venation
eudicots have branching venation

4. Internal Leaf Structure
chlorophyll found in chloroplasts absorbs light

5. Internal Leaf Structure Cont’d…
chlorophyll are found in chloroplasts which are located in the mesophyll (“middle of the leaf”)
palisade mesophyll: closely packed cells just below the upper surface
spongy mesophyll: loosely packed cells in the middle of the leaf

6. Internal Leaf Structure Cont’d…
CO2 enters and O2 exits through special openings called stomata
guard cells surround the stomata bending outward to open the stomata; and collapsing inward to close the stomata

7. Internal Leaf Structure Cont’d…
the outer layer of the leaf is made up of epidermal cells tightly packed in a single layer
do not contain chloroplasts
are transparent, so light can pass through them to the cells within the leaf

8. Internal Leaf Structure Cont’d…
the epidermal cells are covered by a waxy coating called the cuticle
cuticle prevents water loss and provides a physical barrier against bacteria, moulds, and insects

9. Internal Leaf Structure Cont’d…
Some leaves have special adaptations for:
support (i.e. vines)
protection (i.e. needles)
attraction (i.e. to attract pollinators)

10. Homework
Answer 12.2 questions #5-10 on page 551