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Chapter 7 Lecture Outline Leaves Copyright © The McGraw-Hill Companies, Inc. Permission required for reproduction or display. Outline Introduction • Leaf Development • Leaf Parts • Leaf Complexity • Leaf Vein & Leaflet Pattern • Functions of Leaves Leaf Arrangements and Types Internal Structure of Leaves Specialized Leaves Autumnal Changes in Leaf Color Human and Ecological Relevance of Leaves INTRODUCTION LEAF DEVELOPMENT: All leaves originate as primordia in buds. LEAF PARTS (Gross Anatomy) At maturity, most leaves have: • Petiole (rachis) = _________________ – Leaves that are sessile lack a petiole • Lamina = _______________________ • Veins = ________________________ Leaves of flowering plants at nodes also usually have axillary buds at base. LEAF COMPLEXITY • SIMPLE LEAVES = ___________ • COMPOUND LEAVES = _______ LEAF VEIN & LEAFLET PATTERN • PINNATE: ______________ – Simple Pinnate – Compound Pinnate o 1st level o 2nd level • PALMATE: ______________ – Simple Palmate – Compound Palmate Palmately compound 2nd level Compound Pinnate LEAF VEINATION … • PARALLEL: Parallel venation Monocots - Parallel venation Dicots - Pinnate or Palmate. FUNCTIONS OF LEAVES = _______________________________________ • OrganellE: ___________________ • Cell: ___________________ • Need: – _________________ – _________________ – _________________ • Produce: • Stomata function. – Guard Cells • Other functions of leaves: – Wastes disposed of when leaves shed. – Water movement o Transpiration =__________________. Leaf Arrangements and Types Leaves at nodes – Opposite – Alternate – Whorled Alternate Opposite Whorled INTERNAL STRUCTURE OF LEAVES 3 regions: Epidermis, Mesophyll, Veins Epidermis, Herbaceous & Woody plants • Surface coated with __________ • Functions: 1)____________ 2) Water:___________________ 3) Glands • Stomata Internal Structure of Leaves … • Stomata – Location: ___________ – Bordered by two _____________ Cells. o – Have a thickened inner wall Functions: _____________________ « Gas exchange « Evaporation of water How Stomata open & close: • Changes in water content cause them to inflate or deflate. • Rigid inner surface remains stiff Inflate - Stomata open Deflate - Stomata close MESOPHYLL: Region between upper and lower epidermis, excluding the veins. • FUNCTION: __________________________________ • EUDICOTS: TWO SUB-REGIONS 1) Palisade Mesophyll Location: _____ – Shape of cells: ______________ - # Contains chloroplasts – 2) Spongy Mesophyll Location: _______ – Shape of cells: ____________ – Air spaces NOT IN MONOCOTS – Microscopic View of a EUDICOT Mesophyll MONOCOT Mesophyll Vein Chlorencyma Cells VEINS (vascular bundles) • Location: _________________________ • Tissue & Cells: ____________________ – Surrounded by bundle sheath of thicker-walled parenchyma MONOCOT: Zea (Corn) Leaf Guard Cells Vein ZEA VEIN Companion Cells Sieve-Tube Cells Eudicot Vein Vessels Sieve-Tube Cells Companion Cells Differences found in Monocots Flowering plants • Mesophyll noy differentiated into palisade & spongy layers • Stomata on upper & lower epidermis • BULLIFORM CELLS on either side of main central vein • Function: Causes leaf to fold or roll, reducing transpiration Monocot leaf cross section SPECIALIZED LEAVES Shade Leaves Shade • Amount light: – Overall Size: _________ – Thickness: ____ – Have fewer hairs Sun Sun leaf Shade leaf LEAVES OF ARID REGIONS • Problems for plant: – Water: ________________ – Temperatures: ______________ – Light Intensities: _______________ • Leaves reduce loss of water by: – Cuticle: – Thickness: – # Stomata o or sunken stomata – Dense, hairy coverings, often silver LEAVES OF AQUATIC AREAS • Less xylem and phloem • Mesophyll not differentiated into palisade and spongy layers. • Large air spaces TENDRILS • Shape: __________ • Function: _________ Tendrils Examples: Garden peas SPINES • Shape: • Function: Also reduce leaf surface and water loss, – Spine Cacti o Leaf tissue replaced with sclerenchyma. o Photosynthesis occurs in stems. Specialized Leaves Thorns - Modified stems in axils of woody plants Thorn Prickles - Outgrowths from epidermis or cortex Prickle Storage leaves • Succulent leaves: Store ______________ – parenchyma cells with large vacuoles – Many desert plants • Fleshy leaves store ____________. – Onions, lily Flower-Pot Leaves • urn-like pouches: • Ants bring soil & Nit. Wastes: Flower-pot leaf sliced lengthwise Window leaves • Succulent, Africa • Leaves buried in ground. – – End is transparent Function: Reproductive Leaves • Walking fern - New plants at leaf tips • Air plant - Tiny plantlets along leaf margins Air Plant Floral Leaves (bracts) • bases of flowers/flower stalks • Poinsettia - brightly colored bracts surround flowers. • Clary’s sage - Colorful bracts are at top of flowering stalks. Poinsettia Clary’s sage Insect-Trapping Leaves • swampy areas and bogs – Nitrogen is: o Specialized leaves trap and digest insects. • Pitcher Plants – cone-shaped leaves. Pitcher plant Insect-Trapping Leaves • Sundews – leaves covered with glandular hairs have sticky digestive enzymes – Venus’s Flytraps – North Carolina and South Carolina – Mechanically trap insects. Sundew Venus’s Flytraps Insect-Trapping Leaves • Bladderworts – floating in shallow water – bladders have trap doors trap insects inside Bladder of bladderwort Autumnal Changes in Leaf Color Chloroplasts and pigments: • Chlorophylls - Green • Carotenoids - Yellows • In fall, chlorophylls break down and other colors are revealed. anthocyanins (red or blue) and betacyanins (red) may present in vacuole. Human and Ecological Relevance of Leaves STUDENTS READ ON YOUR OWN IN TEXT Review
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