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Plant Tissues Chapter 26 Success of the Angiosperms • The angiosperms are seed-bearing vascular plants • In terms of distribution and diversity, they are the most successful plants on Earth • The structure and function of this plant group help explain its success Plant Life Histories • Annuals complete life cycle in one growing season • Biennials live for two seasons; flowers form in second season • Perennials grow and produce seeds year after year Shoots and Roots • Shoots – Produce food by photosynthesis – Carry out reproductive functions • Roots – Anchor the plant – Penetrate the soil and absorb water and dissolved minerals – Store food Angiosperm Body Plan • Ground tissue system • Vascular tissue system • Dermal tissue system EPIDERMIS VASCULAR TISSUES GROUND TISSUES SHOOT SYSTEM ROOT SYSTEM Meristems • Regions where cell divisions produce plant growth • Apical meristems – Lengthen stems and roots – Responsible for primary growth • Lateral meristems – Increase width of stems – Responsible for secondary growth Apical Meristems • Lengthen shoots and roots • Cells that form at apical meristems – Protoderm – Ground meristem – Procambium activity at meristems new cells elongate and start to differentiate into primary tissues Lateral Meristems • Increases girth of older roots and stems • Cylindrical arrays of cells vascular cambium cork cambium thickening Complex Tissues Composed of a mix of cell types Xylem Phloem Epidermis Xylem • Conducts water and dissolved minerals • Conducting cells are dead and hollow at maturity tracheids vessel member Phloem: A Complex Vascular Tissue sieve plate • Transports sugars • Main conducting cells are sievetube members • Companion cells assist in the loading of sugars sieve-tube member companion cell Monocots and Dicots: 1 cotyledon 4 or 5 floral parts 3 floral parts Parallel veins 1 pore Vascular bundles in ring 2 cotyledons Netlike veins 3 pores Vascular bundles dispersed shoot apical meristem Shoot Development cortex procambrium protoderm procambrium pith ground meristem primary xylem primary phloem Internal Structure of a Dicot Stem • Outermost layer is epidermis • Cortex lies beneath epidermis • Ring of vascular bundles separates the cortex from the pith • The pith lies in the center of the stem Internal Structure of a Monocot Stem • The vascular bundles are distributed throughout the ground tissue • No division of ground tissue into cortex and pith Leaf Gross Structure DICOT MONOCOT petiole axillary bud blade node sheath blade node Adapted for Photosynthesis • Leaves are usually thin – High surface area-to-volume ratio – Promotes diffusion of carbon dioxide in, oxygen out • Leaves are arranged to capture sunlight – Are held perpendicular to rays of sun – Arrange so they don’t shade one another Leaf Structure UPPER EPIDERMIS cuticle PALISADE MESOPHYLL xylem SPONGY MESOPHYLL phloem LOWER EPIDERMIS O2 CO2 one stoma Mesophyll: Photosynthetic Tissue • Cells have chloroplasts • Two layers in dicots – Palisade mesophyll – Spongy mesophyll Leaf Veins: Vascular Bundles • Xylem and phloem; often strengthened with fibers • In dicots, veins are netlike • In monocots, they are parallel Root Systems Root Structure • Root cap covers tip • Apical meristem produces the cap • Cell divisions at the apical meristem cause the root to lengthen • Farther up, cells differentiate and mature Root Hairs and Lateral Roots • Both increase the surface area of a root system • Root hairs are tiny extensions of epidermal cells • Lateral roots arise from the pericycle and must push through the cortex and epidermis to reach the soil new lateral root Secondary Growth • Occurs in all gymnosperms, some monocots, and many dicots • A ring of vascular cambium produces secondary xylem and phloem • Wood is the accumulation of these secondary tissues, especially xylem Secondary Growth Woody Stem periderm (consists of cork, cork cambium, and secondary cortex) BARK vascular cambium secondary phloem HEARTWOOD SAPWOOD Annual Rings • Concentric rings of secondary xylem • Alternating bands of early and late wood • Early wood – Xylem cells with large diameter, thin walls • Late wood – Xylem cells with smaller diameter, thicker walls