Leaves

Tendril – modified leaf found in many vines (peas, pumpkins)

Carnivorous plants – modified leaves that trap insects

Spines – protect plant

Types of leaves

Blade – broad, flat portion; is the site of most photosynthesis

Petiole – attaches most blades to stems

Simple leaf – one bladeCompound leaves – blade is divided into

leafletsIn some species, the leaflets themselves are divided

Leaf Structures

Leaves consist of three tissue systemsDermal – epidermis (single layer with waxy cuticle) with openings called stomata for gas exchange (the number varies by species)Ground – mesophyll (chloroplast-rich parenchyma cells

palisade mesophyll – site of photosynthesis, located directly below epidermis

spongy mesophyll – irregularly spaced cells surrounded by large air spaces

Vascular – in bundles called veins (xylem and phloem)

Venation is the arrangement of veins in a leaf

Monocots – parallelDicots – netted

palmatepinnate

Primary site for photosynthesis in most plantsLeaves that develop in full sun are thicker, have

a smaller area per leaf, and have more chloroplasts per leaf

Dense coating of hairs prevent the absorption of too much sunlight

Leaf Functions

Stoma – opening in cuticle to allow gas exchange

Guard cells – two kidney-shaped cells that regulate the stomaMost plants – stoma open during the day and closed at nightStomata will close if water is scarceIf stomata are closed, virtually no photosynthesis takes place