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Plant Structures Roots, Stems, and Leaves Chapter 23 Types Roots Taproots • Found in dicots • Long, thick root • Hickory and oak trees Fibrous roots • Found in monocots • No single root larger than any other • Many thin roots Root Structure – Outside layer – Epidermis Root hairs Cortex – Central cylinder – vascular system – Root Cap – cellular production Key role in water/mineral transport Root Functions –Anchor plant –Absorb water –Absorb nutrients Essential Plant Nutrients • Plant Nutrient Uptake Soil type determines plant type • Plant requirements Oxygen, CO2 Nitrogen Phosphorus Postassium Magnesium Calcium Trace elements Uptake of Plant Nutrients Active Transport in Plants – Root hairs use ATP Pump minerals from soil Causes water molecules to follow by osmosis Vascular Cylinder – Casparian Strip – water retention Root Pressure – Forces water up into the plant STEMS • Stem Structure – Produce leaves, branches, and flowers – Hold leaves up – Transport substance between roots and leaves • Essential part of transport system • Function in storage and photosynthesis Anatomy of a Stem • Xylem and phloem – major tubule systems Transport water and nutrients • Composed of three tissue layers Contain nodes – attachment for leaves Internodes – regions between the nodes Buds – undeveloped tissue Stem Types Monocot – vascular bundles are scattered throughout Distinct epidermis Dicot – vascular tissue arranged in a cylinder – Pith – parenchyma cells inside the ring Stem Growth • Primary growth – new cells produced at the root tips and shoots Increases the length • Secondary growth – increase in stem width Vascular cambium – produces tissue and increases thickness Cork cambium – produces outer covering of stems Formation of Vascular Cambium – Xylem and phloem bundles present initially – Secondary growth initiates production of a thin layer – The vascular cambium divides Produces new xylem and phloem Leaves • Main site of photosynthesis • Consist of: Blade – thin flattened section Petiole – stalk that attaches stem to blade • Covered by epidermis and cuticle Create water proof barrier Leaf Functions • Photosynthesis – occurs in the mesophyll Palisade mesophyll – absorb light Spongy mesophyll – beneath palisade level Stomata – pores in the underside of the leaf Guard Cells – Surround the stomata Transpiration • Loss of water through its leaves • How does the water that is lost through transpiration get replaced? Gas Exchange • Take in CO2 & release O2 • Can also do the opposite – How? • Gas exchange takes place at the stomata Not open all the time • Stomata is controlled by water pressure in guard cells Plant Tissue Systems • DERMAL TISSUE • VASCULAR TISSUE • GROUND TISSUE Dermal Tissue • protective outer covering of a plant. • young plants consists of a single layer of cells, called the epidermis • cuticle thick waxy layer protects against water loss • older plants dermal tissue may be many cell layers deep may be covered with bark Vascular Tissue • supports the plant body • transports water and nutrients throughout the plant • Xylem water-conducting tissue • Phloem a tissue that carries dissolved food. Both xylem and phloem consist of long, slender cells that connect almost like sections of pipe, as shown in the figure. Xylem: Tracheids • all seed plants have xylem cells called tracheids • as they mature, tracheids die, leaving only their cell walls cell walls contain lignin, a complex molecule that gives wood much of its strength. Xylem: Tracheids • openings in the walls connect neighboring cells • allow water to flow from cell to cell Xylem: Vessel Elements • wider than tracheids and are arranged end to end on top of one another like a stack of tin cans • after they mature and die, cell walls at both ends are left with slit-like openings through which water can move freely Xylem: Sieve Tube Elements • xylem cells, phloem cells are alive at maturity • arranged end to end, forming sieve tubes. end walls have many small holes through which nutrients move from cell to cell Xylem: Sieve Tube Elements As sieve tube elements mature, they lose their nuclei and most other organelles. The remaining organelles hug the inside of the cell wall and are kept alive by companion cells. Phloem: Companion Cells • cells that surround sieve tube elements • keep their nuclei and other organelles through their lifetime Ground Tissue • produces and stores sugars • contributes to physical support of the plant • Three types of ground tissue parenchyma (thin cell walls) collenchyma (thicker cell walls) sclerenchyma (thickest cell walls) Plant Growth and Meristems Meristems • regions of unspecialized cells in which mitosis produces new cells that are ready for differentiation • found in places where plants grow rapidly, such as the tips of stems and roots Apical Meristems • Because the tip of a stem or root is known as its apex • unspecialized cells produced in apical meristems divide rapidly as stems and roots increase in length. Apical Meristems • At first, the new cells that are pushed out of meristems look very much alike • They are unspecialized and have thin cell walls • Gradually, they develop into mature cells with specialized structures and functions. As the cells differentiate, they produce each of the tissue systems of the plant, including dermal, vascular, and ground tissue.