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Botany10 Chp 26 Plant Structure 235,000 species +/-, very diverse forms. Plant bodies divided into roots and shoot systems. Contain diffentiatyed tissues and vascular systems. herbaceous vs woody plants herbaceous plants have no woody tissue, are either annuals, biennials or perennials woody plants are all perennials root systems – fibrous and taproots (storage roots) StemsNode – where leaf attaches Internode – space on stem between nodes Terminal bud – shoot at tip of stem Bud scales- modified leaves that protect the dormant terminal bud Lateral buds- located in the axils of leaves, if they grow they become branches Bud scale scars – Leaf scarsLenticels- allow oxygen to diffuse into stem (woody stems) LeavesBlade and petiole Simple leaves have an undivided blade Compound leaves have a blade divided into at least two or more leaflets Use lateral buds to determine if a leaf is simple or compound…compound leaflets form in a single plane. Leaf arrangements (see figure 26-4 on page 509) Alternate or opposite Whorled Venation Parallel (moncots) Netted – (dicots) palmately netted or pinnately netted (figure 26-6) TISSUES A tissue is a group of cells that form a structural and functional unit, tissues may be comprised of just one type of cell or of several cell types. (see discussion of tissue types on page 510) ground tissue system, vascular tissue system and dermal tissue system. Ground Tissues System – Parenchyma found throughout the plant, perform important functions such as photosynthesis, storage and secretion Collenchyma cells combine to provide structural support, particular in herbaceous plants Sclerenchyma – hard structural support. Vascular Tissue SystemXylem phloem Dermal Tissue System – Epidermis and Periderm Epidermis usually single layer of cells, herbaceous plants and young woody plants, epidermis secretes a waxy layer called a cuticle. Carbon dioxide, oxygen and water vapor enter/escape through the cuticle via stomata. Guard cells are found at the opening of the stoma, open during the day and closed at night…usually. Epidermis may also have trichomes; outgrowths such as hairs or spikes that serve a wide variety of purposes Periderm many cell layers thick – woody plants…replaces epidermis as woody plant matures PLANT GROWTH (for interesting web site with info on recent advances in plant development see www.edoc.com/plantcell/abs/v9n7/981.html or for a discussion on germination and primary growth try http://research.umbc.edu/~farabaug/growth.htm) 3 different processes – cell division, cell elongation and cell differentiation Plants grow differently than animals…plants grow in localized areas called meristems. Cells in meristems do not differentiate. Meristematic cells retain the abiltiy to divie by mitosis. Plants continue to grow throughout their life spans. Primary Growth – increase in the length of a plant, occurs at the apical meristems (herbaceous plants) Secondary growth – increase in the girth of a plant, occurs at the lateral meristems (woody plants) LEAVES – Chp 27 (for more information about leaf anatomy and morphology look at www.botant.uwc.ac.za:80/sci_ed/std8/anatomy/leaves.htm or http://koning,ecsu.ctstateu,edu/Plants_Human/MorpAnat.html or a leaf library at www.onyxtree.com?leaf.html Upper epidermis and lower epidermis. Because of large surface area needed for photosynthetic processes (collection of light & gas exchange) the surface area is prone to water loss. The cuticle reduces this tendency. Cuticle thickness varies between upper and lower leaf surfaces. Trichomes – Stomata - guard cells open and close. Guard cells are the only sells in the epidermis that have chloroplasts. There are more stomata on the lower surfaces of leaves. Mesophyll- photosynthetic tissue of the leaf, between upper and lower surfaces. (see discussion on pg 528) Vascular system of xylem and phloem pass through the mesophyll in leaves. Xylem is usually toward the upper epidermis and phloem toward the lower., The viens are surrounded by cells called a bundle sheaf DICOTS AND MONOCOTS Characteristic Leaf shape Attach to stem Veins Mesophyll Monocot Narrow leaves Wrap around stem Parallel Not differentiated Dicot Broad flattened leaf Petiole Netted Contains both palisade and spongy layers For more on monocots and dicots look at www.ucmp.berkeley.edu/glossary/gloss8/monocotdicot.html Structure is related to function in leaves – pg 530 Photosynthesis – epidermis is transparent allowing light to penetrate to the interior of the leaf. The stomata allow carbon dioxide into the leaf and oxygen back out (gas exchange). Water is transported to the leaf through the xylem and sugars produced prom photosynthesis are distributed via the phloem. Transpiration - 99% of the water absorbed from the soil by roots is lost from evaporation, primarily through the leaves. Loss of water vapor from the above ground portions of a plant is called transpiration. Guttation – pg 534 when transpiration is low and water quantity is high Abscission – leaves are lost because of reduced water availability, it is a measure of water conservation…see abscission zone on pg 535.