LEAVES Photosynthetic organs of plants

Basic Leaf Structure Axillary bud 

Leaf Types Simple – single blade Simple – single blade Compound – 2 or more leaflets Compound – 2 or more leaflets *Look for petiole & bud *Look for petiole & bud 2 kinds: 2 kinds: Pinnate Pinnate Palmate Palmate

Leaf Cross-Section

Leaf Epidermis Upper and lower surface of leaf covered by epidermis Upper and lower surface of leaf covered by epidermis Most cells lack chloroplasts and are transparent Most cells lack chloroplasts and are transparent Cells secrete cuticle made of waxy cutin Cells secrete cuticle made of waxy cutin Many leaves have hairlike trichomes Many leaves have hairlike trichomes May reduce water loss May reduce water loss May produce irritants – discourage herbivores May produce irritants – discourage herbivores

Stomata Tiny openings for gas exchange Tiny openings for gas exchange Flanked by guard cells Flanked by guard cells Most numerous on lower epidermis of horizontal leaves Most numerous on lower epidermis of horizontal leaves

Mesophyll: The middle layer Made of photosynthetic ground tissue Made of photosynthetic ground tissue Divided into 2 sublayers: Divided into 2 sublayers: Palisade mesophyll Palisade mesophyll Spongy mesophyll Spongy mesophyll

Vascular Bundles Veins extend throughout the mesophyll Veins extend throughout the mesophyll Contains: Contains: Xylem – toward the top of vein Xylem – toward the top of vein Phloem – toward the bottom of vein Phloem – toward the bottom of vein Bundle sheath - 1 or more layers of cells surrounding the larger veins Bundle sheath - 1 or more layers of cells surrounding the larger veins Made of parenchyma or schlerenchyma cells Made of parenchyma or schlerenchyma cells

Monocot vs. Dicot MONOCOT Base of leaf wraps around stem in a sheath (lack petiole) Base of leaf wraps around stem in a sheath (lack petiole) Some monocots do not have distinct palisade and spongy layers Some monocots do not have distinct palisade and spongy layersDICOT Broad flattened blade and petiole Broad flattened blade and petiole Palisade and spongy layer Palisade and spongy layer Guard cells shaped like kidney beans Guard cells shaped like kidney beans

LEAF ADAPTATIONS Cuticle Cuticle Placement of stomata Placement of stomata Needles vs. leaves Needles vs. leaves Length of petioles Length of petioles

Modified Leaves Spines Spines Tendrils Tendrils Bulbs Bulbs Carnivorous Carnivorous