24 1 The Plant Body is Organized and Constructed in a Distinctive Way Plants are stationary sessile Stems leaves and roots have structural adaptations that enable plants anchored to one spot to capture scarce resources effectively both above and below ground Ability to grow throughout lifetime enables plants to respond to environmental cues by redirecting their growth to exploit environmental opportunities a when roots grow toward a water supply Anchors plant absorbs water and dissolved minerals and stores the products of Plant organs organized into two systems Root system photosynthesis Shoot system consists of stems leaves and flowers Leaves chief organ of photosynthesis Arise from nodes on stem and between the nodes is called phytomer Stems hold and display leaves to sun and provide connections for transport of materials between roots and leaves Flowers are reproductive organs Angiosperms categorized into two clades Monocots and Dicots Four processes that govern the development of all organisms are Determination the commitment of an embryonic cell to its ultimate fate in organism Differentiation the specialization of a cell Morphogenesis the organization and spatial distribution of cells into tissues and organs Growth increase in body size In plants these processes influenced by apical meristems cells walls and totipotency of most cells Apical meristems always embryonic and produces new roots stems leaves and flowers throughout plant s lifetime Cells walls Rigid extracellular matrix that makes it impossible for cells to move place to place Plant morphogenesis occurs which changes direction in which tissue grows Plant cytokinesis occurs along cell plate Location of plant cell plate is determined as early as mitotic prophase Totipotency All cells in plants even differentiated cells are pluripotent can readily repair damage caused by environment or herbivores Two patterns of plant embryo formation Apical basal axis arrangement of cells and tissues along he main axis from root to shoot Radial axis concentric arrangement of tissue systems Formation of plant embryo Mitotic division of zygote gives rise to 2 daughter cells Apical upper daughter cells produces embryo proper other produces supporting structure In dicots cotyledon begins to grow between cotyledons are shoot apical meristem and root called the suspensor apical meristem Plant tissues dermal vascular and ground Dermal tissue system Epidermis outer covering of plant Usually consists of single layer Epidermal cells can differentiate to form Stomata pores for gas exchange in leaves Trichomes leaf hairs provide protection against insects and damaging solar Roots hairs increase root surface area providing more surface for uptake of water radiation and mineral nutrients Cuticle made of cutin polymer composed of long chains of fatty acids Limits water loss reflects solar radiation ad serves as barrier against pathogens Stems and roots of woody plants develop dermal tissue called periderm Forms cork layer impermeable to water and gases Ground Tissue System most of plant body 3 cells types Parenchyma most abundant ground tissue cells large vacuoles and ting cell walls perform photosynthesis in shoot and store protein in fruits and starch in roots Collenchyma elongated cells that have thick cell walls provide support for growing tissues such as stems Schlerenchyma cells have thick walls reinforced with polypherol polymer lignin most cells undergo programmed cell death apoptosis but strong cells walls provide support two types of schlerenchma cells fibers and sclereids elongated fibers provide rigid support to parts of plants organized into bundles Sclereids occur in various shapes and may pack together densely isolated clumps of sclereid called stone cells give pears and other fruits gritty texture Vascular Tissue System Xylem distributes water and mineral ions taken up by roots to all cells of roots stems and leaves Made up of dead cells Contains two type of conducting cells Tracheids spindle shaped cells w thinner regions in cell wall called pits through which water can move with little resistance from one tracheid to its neighbors Vessel elements larger in diameter than tracheids meet end to end and partially break down their end walls forming open Phloem consists of living cells pipeline for water conduction transport carbohydrates primarily sugars from sites produced by photosynthesis to sites where they are used or stored characteristic cell is sieve tube elements which meet end to end forming sieve tubes connected by plasmodesmata which form set of pores called sieve plate 24 2 Meristems Build Roots Stems and Leaves All plants experience primary growth lengthening of roots and shoots by proliferation of new roots and shoots through branching Secondary growth increase in thickness Plant that results entirely from primary growth consists of nonwoody issues and is referred to as herbaceous Two types of meristems contribute to growth and development Apical meristems orchestrate primary growth giving rise to primary plant body Growth characterized by cell division followed by cell expansion Lateral meristems orchestrate secondary growth Two lateral mersitems vascular cambium and cork cambium Growth of shoot or root is indeterminate Division Expansion Differentiation Three primary meristems protoderm ground meristem procambium These meristems give rise to 3 tissue systems Protoderm Dermal tissue Ground meristem Ground tissue system Procambrium Vascular tissue system Root apical meristem gives rise to root cap and three primary meristems Root cap protects delicate growing region of root as it pushes through soil cells of root cap often damaged and replaced constantly detects pull of gravity and controls downward growth of roots Apical and primary meristems constitute zone of cell division Zone of elongation newly formed cells elongating and pushing root farther into soil Zone of cell maturation cells differentiating Products of three primary meristems are tissue systems of mature root epidermis cortex stele Protoderm gives rise to epidermis outer layer of cells that protect root and absorb mineral ions and water Ground meristem gives rise to cortex parenchyma cells of cortex relatively unspecialized and often serve as storage depots inner most layer is endodermis cells walls of endodermal cells contain suberin waterproof substance Interior to endodermis is vascular cylinder or stele Vascular tissues contained within stele