Plant Anatomy: Vegetative Organs Leaves: Stem: Photosynthesis Support BI 103: Leaves Gas exchange Transport Light absorption Storage An examination of leaves Chapter 43 cont. Roots: Anchorage Storage Form = Function Transport Absorption Introduction Adapted for Photosynthesis • Other functions of leaves: • Leaves are usually thin – Wastes from metabolic processes accumulate in leaves and are disposed of – High surface area-to-volume when leaves are shed. ratio – Promotes diffusion of carbon – Play major role in movement of water dioxide in, oxygen out absorbed by roots • Transpiration occurs when water evaporates • Leaves are arranged to from leaf surface. capture sunlight • Guttation - Root pressure forces water out hydathodes at tips of leaf veins in some plants. – Are held perpendicular to rays of sun – Arranged so they don’t shade one another Common Leaf Forms Internal Anatomy of Leaves Specialized structures: DICOT MONOCOT • Veins petiole axillary – surrounded by bundle sheath bud blade • Mesophyll node • Stomata– openings for gas exchange blade sheath node 1 leaf blade Leaf Vein (one vascular bundle) cuticle Epidermis: Cuticle leaf vein Upper Epidermis Palisade • Waxy cuticle secreted by epidermis cells Mesophyll stem • Protective layer against disease xylem Spongy • Reduced water loss from cells Water, dissolved Mesophyll mineral ions from roots and stems move into leaf Lower vein (blue arrow) Epidermis 50m phloem cuticle-coated cell of lower epidermis Photosynthetic products (pink one stoma (opening arrow) enter across epidermia) vein, will be Carbon transported Oxygen and water vapor dioxide in throughout outside air plant body diffuse out of leaf at enters leaf at stomata. stomata. Fig. 29-14, p.501 Guard Cells 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. Vascular plants: have stomata Bryophytes: pores bordered by 2 guard cells • Bryophytes like moss and liverworts lack stomata • Have pores that are always open Cross section of liverwort thallus (Conocephalum) Open when water is abundant. Close when water is scarce. 2 Epidermis: Trichomes Trichomes Glandular trichome of Stinging Nettle Urtica dioica 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 Mesophyll=ground tissue Epidermal tissue: Prickles Most photosynthesis takes Prickles: epidermal place in the mesophyll between the cells- larger tichomes two epidermal layers. Examples: Rosa spp. 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 Photosynthesis: The Components What are the inputs? ? ? ? What are the outputs? ? ? 3 Light is a wave of energy: Photosynthesis: The Components colors are different wavelengths 6CO2 + 6H2O + Light energy C6H12O6 + 6O2 What are the inputs? - light - water - carbon dioxide What are the outputs? - glucose - oxygen Photosynthesis: Input - Light Photosynthesis: Light Absorption The color you see Intensity Plants are green because… • Reflect green light. • Absorb red, blue and purple light. Energy (wavelength) absorbed Photosynthesis: Light Absorption Leaf Veins: Vascular Bundles Plant pigments absorb light…. • Xylem and phloem; often strengthened with fibers • In dicots, veins are netlike • In monocots, they are parallel Absorb red, blue and purple light Reflect green light 4 Specialized Leaves Specialized Leaves: Carnivorous Carnivorous leaves Sundews • Grow in swampy areas • Have round to oval leaves covered with glandular and bogs hairs that have a sticky • Nitrogen and other fluid of digestive enzymes elements are deficient in at tip soil. Sundew • Specialized leaves trap Venus’s Flytraps and digest insects. • Only in North Carolina and South Carolina – Pitcher Plants • Blade halves trap insects. • Insects trapped and digested inside cone- Pitcher plant shaped leaves. Venus’s Flytraps Specialized Leaves Specialized Leaves: Bracts • Floral Leaves (bracts) Example: Flowering dogwood, Cornus nutallii – 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 Specialized Leaves • Leaves of Arid Regions • Leaves of Arid Regions – Conifers Tsuga canadensis – Sunken stomata – 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 Picea 5 Specialized Leaves Specialized Leaves • Leaves of Aquatic Areas Tendrils – Less xylem and phloem – Mesophyll not differentiated into palisade and spongy layers. – Large air spaces Water lily leaf Tendrils Elodea leaf Spines Thorn Thorns - Modified stems arising in the axils of leaves of woody plants Spine 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. 6 .