#6 Plant structure - Lecture notes 6 PDF

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Plant structure and function A plants growth is directed by enivro. cues: - development of plants depends on the enviro. and is highly adaptive What makes a plant a plant: - resources needed by animals: - carbon + energy — from food - water — from water sources + food - 02 — from air and water - —> available in concentrated form - resources needed by plants: - carbon — from air - energy — from light - water — from soil - minerals — from soil - —> dilute, dispersed, available only part of the time How they get these resources: - diffusion of resources from enviro. to plant = rate limiting step in plant growth - dendritic form (branching growth habit): helps diffusion (branching body explores larger volume of space) - fanwort (cabomba caroliniana): developmental plasticity (= effect of enviro. on development) evident: forms dif. leaves depending on whether or not apical meristem is submerged Development: consists of growth, morphogenesis and cell differentiation: - growth: irreversible increase in size - morphogenesis: development of body form and organization - cell differentiation: process by which cells w/ the same genes become dif. from each other, becoming specialized in form and function Two main systems of plants: 1) shoot system: - stems + leaves - photosynthesis - vegetative (leaf bearing) or reproductive (flower bearing) 2) root system: - anchor - mineral + water absorption - food storage ** Know terms + functions: Shoot system: Apical bud (top), Node, Internode, Axillary bud (bottom), Leaf: blade + petiole, Root system: Taproot, Lateral (branch) roots

Three basic organs of plants: 1) roots 2) stems 3) leaves Root systems: 1) taproot system - eudicots + gymnosperms - one large vert. root (taproot) that produces many smaller lateral (branch) roots - taproots often store food (ex. carrots) 2) fibrous root system - seedless vascular plants + most monocots - mat of thin roots that spread out below the surface - > Root hairs: - near root tips - most absorption of water + minerals - increase surface area - extension of individual epidermal cells lateral roots = multicellular organs - > Adventitious roots: (L. adventicius : extraneous) - above ground - arise from stems/leaves Shoot systems: stems: - alternating system of nodes and internodes - nodes: points at which leaves are attached - internodes: stem segment between nodes - axillary bud: - in axil between each leaf +stem - potential to form vegetative branch - dormant in young shoots - terminal bud: - at shoot apex - developing leaves + compact series of nodes + internodes - inhibits growths of axillary buds - —> apical dominance —> resources concentrated on growing taller, increases plants exposure to light Modifed stems: - bulbs: (ex. onion) - vertical, underground shoots - consist mostly of swollen bases of leaves that store food - rhizomes: (ex. edible base of ginger) - horizontal stems that grow underground - stolons: (ex. runners of strawberries) - grow on surface of soil - asexual reproduction

- tubers (ex. potatoes) - swollen ends of rhizomes specialized for food storage Shoot system: leaves: - main photosynthetic organ of most plants - flattened blade plus stalk (petiole) - petiole absent in some monocots (ex. grass) - arrangement of major veins: monocots = parallel, eudicots = branched network - one axillary bud/leaf, can form a lateral shoot = branch - simple lead: single, undivided blade - compound leaf: blade divided into leaflets Modified leaves: - Spines: (ex. cactus) - protection - Reproductive leaves: (Kalanchoe) - Tendrils (ex. pea) - cling to other structures - Storage leaves: (ex. onion)

- modification for water storage (ex. succulents) - attraction for pollinators, leaves brightly coloured (ex. Poinsettia) Plant organs are composed of three tissue systems: 1) Dermal Tissue (epidermis): cover + protection - covers entire body of plant - single layer of tightly packed cells - first line of defence against physical damage + pathogens - specializations characteristics of organ function - root: root hairs - leaves and stems: - secretion of waxy cuticle, helps prevent water loss - woody plants: periderm replaces epidermis in older regions - guard cells in leaves - trichomes: reduce water loss, reflect excess light, defends 2) Ground Tissue: most metabolic functions - between dermal + vascular tissue - pith: internal to vascular tissue - cortex: external to vascular tissue 3) Vascular Tissue: transport of materials - arranged differently in each organ - stele: vascular tissue of root + stem - each tissue system is continuous throughout plant

Plant cell = protoplast + cell wall: - protoplast: cell contents exclusive of the cell wall - between cell sap (in vacuole) + cytosol - cytosol + organelles (ex. chloroplasts) - vacuole: uptake of water —> occupies large volume w/o diluting cytoplasmic contents - tonoplast (membrane around vacuole): regulates traffic of molecules - cell walls: hold up the plant - thin-walled, water-inflated cells: good building material - thick-walled cells: self-supporting - —> protection, maintenance of shape, prevention of excessive water uptake, support of whole plants - plasmodesmata: connection between adjacent cells Plant cell wall: - important determinant of plant structure and function - primary wall: - origin in cell division - components: cellulose fibrils in amorphous metric - thin + flexible - source of strength of tissues containing only primary cell walls: cells are inflated with water - secondary wall: - not all cells have one - laid down inside the primary wall - components: cellulose + lignin - good tensile strength - self-supporting - doesn’t not need to be inflated Common types of plant cells: - Parenchyma cells: least specialized cells - primary walls: thin + flexible - protoplast w/ large central vacuole - alive when mature - perform most of the metabolic functions: - photosynthesis - starch storage in stems + roots - fleshy tissue of fruit - developing cells - repair + replacement of organs - Collenchyma cells: support young shoot w/o restraining growth - grouped in strand or cylinders - primary walls: thicker than in Parenchyma cells, uneven thickness, lack lignin - living + flexible at functional maturity

- Selerenchyma cells: support - secondary walls: thick, strengthened by lignin - more rigid than collenchyma cells - occur in regions that have stopped growing - many dead at functional maturity - fibers: long, spender, tapered, occur in groups - sclereids: shorter, irregular shape...