BI 103: Leaves An examination of leaves Chapter 43 cont. Learning Objectives What is the function of the plant leaf? How are specific cells and tissues adapted in the leaf in order to help it function? What do plants need to photosynthesize? How are tissues in the leaf different from the roots & stem? What are examples of specialized leaves? 1
Plant Anatomy: Vegetative Organs Leaves: Photosynthesis Gas exchange Light absorption Stem: Support Transport Storage Roots: Anchorage Storage Transport Absorption Form = Function Introduction Other functions of leaves: Wastes from metabolic processes accumulate in leaves and are disposed of when leaves are shed. Play major role in movement of water absorbed by roots Transpiration occurs when water evaporates from leaf surface. Guttation - Root pressure forces water out hydathodes at tips of leaf veins in some plants. 2
Adapted for Photosynthesis Leaves are usually thin High surface area-to-volume ratio Promotes diffusion of gases Leaves are arranged to capture sunlight Are held perpendicular to rays of sun Arranged so they don t shade one another Common Leaf Forms DICOT petiole axillary bud node MONOCOT blade blade sheath node 3
leaf blade leaf vein Leaf Vein (one vascular bundle) cuticle Upper Epidermis Palisade Mesophyll stem xylem Water, dissolved mineral ions from roots and stems move into leaf vein (blue arrow) Spongy Mesophyll Lower Epidermis phloem 50 m Photosynthetic products (pink arrow) enter vein, will be transported throughout plant body Oxygen and water vapor diffuse out of leaf at stomata. Carbon dioxide in outside air enters leaf at stomata. cuticle-coated cell of lower epidermis one stoma (opening across epidermia) Fig. 29-14, p.501 Epidermis: Cuticle Waxy cuticle secreted by epidermis cells Protective layer against disease Reduced water loss from cells 4
Dermal tissue Epidermis - Single layer of cells covering the entire surface of the leaf Devoid of chloroplasts Coated with cuticle Functions to protect tissues inside leaves Waste materials may accumulate in epidermal cells. Different types of glands may also be present in the epidermis. Guard Cells 5
Vascular plants: have stomata bordered by 2 guard cells Open when water is abundant. Close when water is scarce. Bryophytes: pores Bryophytes like moss and liverworts lack stomata Have pores that are always open Cross section of liverwort thallus (Conocephalum) 6
Epidermis: Trichomes Trichomes on an Arabidopsis leaf. Trichomes are extensions from the plant's epidermis and they occur in numerous shapes and sizes in various plants. Trichomes may provide defense against insects Trichomes Glandular trichome of Stinging Nettle Urtica dioica 7
Epidermal tissue: Prickles Prickles: epidermal cells- larger tichomes Examples: Rosa spp. Mesophyll Most photosynthesis takes place in the mesophyll between the two epidermal layers. I. Palisade Mesophyll Compactly stacked, barrel-shaped parenchyma cells, commonly in two rows Contains most of leaf s chloroplasts II. Spongy Mesophyll Loosely arranged parenchyma cells with abundant air spaces 8
? Photosynthesis: The Components?? What are the inputs? What are the outputs??? 9
Photosynthesis: The Components 6CO 2 + 6H 2 O + Light energy C 6 H 12 O 6 + 6O 2 What are the inputs? - light - water - carbon dioxide What are the outputs? - glucose - oxygen Light is a wave of energy: colors are different wavelengths 10
Photosynthesis: Input - Light Intensity The color you see Energy (wavelength) absorbed Photosynthesis: Light Absorption Plants are green because Reflect green light. Absorb red, blue and purple light. 11
Photosynthesis: Light Absorption Plant pigments absorb light. Absorb red, blue and purple light Reflect green light Leaf Veins: Vascular Bundles Xylem and phloem; often strengthened with fibers In dicots, veins are netlike In monocots, they are parallel 12
Specialized Leaves Carnivorous leaves Grow in swampy areas and bogs Nitrogen and other elements are deficient in soil. Specialized leaves trap and digest insects. Pitcher Plants Insects trapped and digested inside coneshaped leaves. Pitcher plant Specialized Leaves: Carnivorous Sundews Have round to oval leaves covered with glandular hairs that have a sticky fluid of digestive enzymes at tip Sundew Venus s Flytraps Only in North Carolina and South Carolina Blade halves trap insects. Venus s Flytraps 13
Floral Leaves (bracts) Specialized Leaves At bases of flowers or flower stalks Poinsettia - Flowers do not have petals, instead brightly colored bracts surround flowers. Clary s sage - Colorful bracts are at top of flowering stalks above flowers. Poinsettia Clary s sage Specialized Leaves: Bracts Example: Flowering dogwood, Cornus nutallii 14
Specialized Leaves Leaves of Arid Regions Arid regions have limited availability of water, wide temperature ranges, and high light intensities. Leaves reduce loss of water by: Thick, leathery leaves Fewer stomata or sunken stomata Succulent, water-retaining leaves, or no leaves Dense, hairy coverings Specialized Leaves Leaves of Arid Regions Conifers Sunken stomata Tsuga canadensis Picea 15
Specialized Leaves Leaves of Aquatic Areas Less xylem and phloem Mesophyll not differentiated into palisade and spongy layers. Large air spaces Water lily leaf Elodea leaf Tendrils Specialized Leaves Spines Tendrils Thorns - Modified stems arising in the axils of leaves of woody plants Thorn Spine 16
Autumnal Changes in Leaf Color Chloroplasts of mature leaves contain several groups of pigments: Chlorophylls - Green Carotenoids - Yellows In fall, chlorophylls break down and other colors are revealed. Water soluble anthocyanins (red or blue) and betacyanins (red) may also be present in the vacuole. 17