Chapter 35 Plant Structure Growth and Development Plants respond to environment by altering their growth plants grow on illuminated side but not the shaded side 35 1 PLANTS HAVE A HIERARCHIAL ORGANIZATION CONSISTING OF ORGANS TISSUES AND CELLS An organ consists of several types of tissues that together carry out particular functions A tissue is a group of cells consisting of one or more cell types that together perform a specialized function THE THREE BASIC PLANT ORGANS ROOTS STEMS AND LEAVES Basic morphology of vascular plants reflects evolutionary history as terrestrial organisms that inhabit and draw resources from above the ground and below the ground Water and minerals must be absorbed below the ground and CO2 and light from above the ground Evolution of roots stems and leaves helps trace the ability to acquire resources The roots form a root system while leaves and stems form a shoot system Vascular plants rely on both systems for survival roots are not photosynthetic they starve unless photosynthesis sugars and carbohydrates is imported from the shoot system The shoot system depends on the water and minerals that absorb from the soil Roots A root is an organ that anchors a vascular plant in the soil absorbs minerals and water and often stores carbohydrates and other reserves The PRIMARY ROOT is the first root to emerge from the seed embryo It branches off to form LATERAL ROOTS which enhance the ability to obtain resources and anchor the plant Tall erect plants consist of a TAPROOT SYSTEM which consists of one main vertical root TAPROOT which develops from the primary root and helps anchor it In TAPOOT SYSTEMS only the lateral root absorbs Taproots are expensive to make energy wise but allow it to grow taller and give it reproductive and resourceful advantages Short plants have a FIBROUS ROOT SYSTEM a thick mat of slender roots spreading out below soil surface In plants that have this the primary root dies early and does not form a taproot instead many small roots emerge and are said to be ADVENTITIOUS Each root forms its own lateral roots and so on They are useful for holding topsoil in place ROOT HAIRS thin finger like extensions of root epidermal cells at the tips of elongating roots emerge and increase the surface area of the root enormously Most terrestrial plant root systems also form mycorrhizial associations Many roots of different plant species have specialized functions Stems A stem is a plant organ bearing leaves and buds and its main function is to elongate and orient the shoot in a way that maximizes photosynthesis by leaves Also it elevates reproductive structures and aids in the dispersal of pollen and fruit Each stem consists of an alternating system of NODES the points at which leaves are attached and INTERNODES the stem segments between nodes The APICAL BUD near the growing tip is where most growth of the young shoot is concentrated THE AXILLARY BUD is formed by each leaf and stem and can potentially form a lateral branch or a thorn or flower Leaves In most vascular plants the leaf is the main photosynthetic organ Leafs also exchange gases with atmosphere dissipate heat and defend plant from pathogens and herbivores Leaves have many functions which could often result in compromises in leaf shape A leaf consists of a flattened BLADE and a stalk the PETIOLE that joins the leaf to the stem at a node Monocots and eudicots differ in the arrangement of veins the vascular tissue of leaves Most monocots have parallel veins that run length of blade while Eudicots have a branched network of veins that branch of major vein midrib Taxonomists rely on floral morphology and often leaf morphology to identify angiosperms Leaf morphology can be broken down into simple vs compound The morphological features of leaves are often products of genetic programs that are tweaked by the environment All leaves are suitable for photosynthesis but some have additional functions DERMAL VASCULAR AND GRAND TISSUE SYSTEMS All 3 basic plant organs are composed of dermal vascular and ground tissues Each tissue type forms a TISSUE SYSTEM that connects all of the plant s organs THE DERMAL TISSUE SYSTEM is the plant s outer protective covering being the first line of defense Non woody plants have a single tissue called the epidermis The Cuticle helps prevent water loss In woody plants PERIDERM protective tissues replaces the epidermis in older regions of stems and roots In root hairs the epidermis aids in the absorption of water and nutrients In shoot systems specialized epidermal cells called guard cells participate in gas exchange TRICHIOMEs are found in shoots and in some desert species reduce water loss and reflect light The VASCULAR TISSUE SYSTEM facilitates the transport of materials through the plant and to provide mechanical support and is made up of XYLEM and PHLOEM XYLEM conducts water and dissolved minerals upward from the roots to the shoots while PHLOEM transports sugars from leaves to the roots and growth sites STELE is the vascular tissue of a root or stem Tissues that are neither dermal nor vascular are part of the GROUND TISSUE SYTEM Ground tissue that is internal to vascular tissue is known as PITH and the one external is called cortex THE GROUND TISSUE SYSTEM INCLUDES CELLS SPECILIZED FOR FUNCTIONS SUCH AS STORAGE PHOTOSYNTHEIS SUPPORT AND SHORT DISTANCE TRANSPORT COMMON TYPES OF PLANT CELLS In multicellular organisms cells undergo CELL DIFFERENTIATION to become specialized The types of Cells are Parenchyma Cells have primary walls that are relatively thin and flexible and most lack secondary walls Perform most of the metabolic functions of plant and synthesize and store various organic materials Collenchyma Cells Help support young parts of the plant shoot Provide flexible support without restraining growth Sclerenchyma Cells Function as supporting elements in the plant Secondary cell wall contains large amounts of lignin strengthening polymers There are 2 types of these cells Sclereids and fibers Sclereids are boxier than fibers and irregular in shape and have very thick lignified secondary cell walls Fibers found in strands are long slender and tapered Water Conducting Cells of Xylem Tracheids and Vessel Elements up the 2 types of water conducting cells and are tubular elongated cells that are dead at functional maturity Tracheids are long thin cells with tapered ends Water moves through pits Vessel elements are wider shorter thinner walled and less tapered than