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Plant Structures Chapter 31 Life Span Annuals – herbaceous (nonwoody) plants that live 1 year only Biennials – take 2 years for life cycle Perennials – can be herbaceous or woody but live longer than 2 years Deciduous – shed leaves before winter Evergreen – some leaves are always present Plant Tissues Three main tissue systems each of which extends throughout the plant and consists of 2 or more kinds of cells Ground tissue – photosynthesis, storage and support Vascular tissue – conduction of water, dissolved nutrients and sugars Dermal tissue – covering for plant body Tissue systems are further arranged into organs: roots, stems, leaves, flowers Ground Tissue Three cell types distinguished by their cell wall structures Parenchyma – living, thin primary cell walls; storage, secretion, photosynthesis Collenchyma – living, unevenly thickened primary cell walls; elastic support Sclerenchyma – often dead at maturity, thick secondary cell walls; support and strength Vascular Tissue Two complex tissues: xylem and phloem Xylem – conducts water and dissolved nutrients Tracheids – conduct water; provide support Vessel elements – wider than tracheid; conduct water; provide support Phloem – conducts food and provides support Sieve tube elements – conduct dissolved sugar Companion cells – helps move sugar in and out of phloem Dermal Tissue Herbaceous plants – a single layer called the epidermis Woody plants – continuous growth of new tissues, covered by a layer of periderm (bark) Epidermal cells - protection Guard cells – open and close stomata Trichome – hairy outgrowths; protection Cork cells – reduces water loss; protection from invading organisms Plant Meristems Specific areas of the plant’s body where growth occurs Cells in these areas divide by mitosis and do not differentiate Plants can grow throughout their life span Two kinds of growth: Primary – increase in stem and root length Secondary – increase in girth Apical meristems Primary growth occurs here Tips of roots and shoots Lateral Meristems Secondary growth occurs here – only in woody plants Vascular cambium – between the wood and bark – adds cells to wood and inner bark Cork cambium – located in the outer bark and produce cork cells and parenchyma cells