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

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

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

Internal Leaf Structure chlorophyll found in chloroplasts absorbs light

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

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

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

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

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)

Homework Answer 12.2 questions #5-10 on page 551