LEAVESLEAVES

Photosynthetic organs of Photosynthetic organs of

plantsplants

Basic Leaf StructureBasic Leaf Structure

Axillary bud

Leaf TypesLeaf Types

Simple – single bladeSimple – single blade

Compound – 2 or Compound – 2 or more leafletsmore leaflets *Look for petiole & *Look for petiole &

budbud 2 kinds:2 kinds:

PinnatePinnate PalmatePalmate

Leaf Cross-SectionLeaf Cross-Section

Leaf EpidermisLeaf Epidermis

Upper and lower surface of leaf covered by Upper and lower surface of leaf covered by epidermisepidermis

Most cells lack chloroplasts and are transparentMost cells lack chloroplasts and are transparent

Cells secrete cuticle made of waxy cutinCells secrete cuticle made of waxy cutin

Many leaves have hairlike trichomesMany leaves have hairlike trichomes May reduce water lossMay reduce water loss May produce irritants – discourage herbivoresMay produce irritants – discourage herbivores

StomataStomata

Tiny openings for gas exchangeTiny openings for gas exchange

Flanked by guard cellsFlanked by guard cells

Most numerous on lower epidermis of Most numerous on lower epidermis of horizontal leaveshorizontal leaves

Mesophyll:Mesophyll:The middle layerThe middle layer

Made of photosynthetic ground tissueMade of photosynthetic ground tissue

Divided into 2 sublayers:Divided into 2 sublayers:

Palisade mesophyllPalisade mesophyll

Spongy mesophyllSpongy mesophyll

Vascular BundlesVascular Bundles

Veins extend throughout the mesophyllVeins extend throughout the mesophyll

Contains:Contains: Xylem – toward the top of veinXylem – toward the top of vein Phloem – toward the bottom of veinPhloem – toward the bottom of vein

Bundle sheath - 1 or more layers of cells Bundle sheath - 1 or more layers of cells surrounding the larger veinssurrounding the larger veins Made of parenchyma or schlerenchyma cellsMade of parenchyma or schlerenchyma cells

Monocot vs. DicotMonocot vs. Dicot

MONOCOTMONOCOT Base of leaf wraps Base of leaf wraps

around stem in a sheath around stem in a sheath (lack petiole)(lack petiole)

Some monocots do not Some monocots do not have distinct palisade have distinct palisade and spongy layersand spongy layers

DICOTDICOT Broad flattened blade Broad flattened blade

and petioleand petiole Palisade and spongy Palisade and spongy

layerlayer Guard cells shaped like Guard cells shaped like

kidney beanskidney beans

LEAF ADAPTATIONSLEAF ADAPTATIONS

CuticleCuticle

Placement of stomataPlacement of stomata

Needles vs. leavesNeedles vs. leaves

Length of petiolesLength of petioles

Modified LeavesModified Leaves

SpinesSpines

TendrilsTendrils

BulbsBulbs

CarnivorousCarnivorous