Plant Structure and Function PDF

Plant Structure & Function  Plants have a hierarchical organization consisting of organs, tissues, and cells Plants have organs composed of different tissues, which are composed of different cell types An organ consists of several types of tissues that together carry out particular fu...

Plant Structure & Function  Plants have a hierarchical organization consisting of organs, tissues, and cells Plants have organs composed of different tissues, which are composed of different cell types 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 Four Basic Parts of Plants Leaves Stems Roots Flowers  Angiosperms (flowering plants) Angiosperms the most diverse and widespread of all plants. The two major angiosperm classes are: monocots - possess a single seed leaf (cotyledon), for example wheat dicots (eudicots) - possess a double seed leaf, for example beans  Leaves Functions – Make food through photosynthesis – Site of gas exchange Respiration Photosynthesis – Store food Tissues of the Leaf Tissues of the Leaf: Epidermis Cuticle – Waxy substance that covers the leaves & stems – Waterproof layer that keeps water in plants  Tissues of the Leaf: Epidermis Stomata – Openings in the epidermis mainly located on the underside of leaves – Exchange of gases Guard Cells – Two cells located on each side of stomata – Open and closes stomata  Tissues of the Leaf: Mesophyll 1. Palisade mesophyll upright cells Primary site of photosynthesisEpidermis 2. Spongy mesophyll loosely organized cells with air spaces Site of photosynthesis and gas exchange Epidermis  Tissues of the Leaf Vascular Bundles – Called veins – Phloem moves food from leaf to the rest of the plant – Xylem moves water & minerals up to leaves from roots  Vein Structure Xylem: dorsal Phloem: ventral Often surrounded by bundle sheath cells for support  Xylem Phloem Bundle Sheath Cells Collenchyma  Plant Cell Types Differentiated by the type and thickness of the cell wall 1. Parenchyma (soft tissue) 2. Collenchyma (glue tissue) 3. Sclerenchyma (hard tissue)  Parenchyma Cells Primary wall only. Thin cell wall “typical" plant cell  Collenchyma Wall is thickened, especially in the corners Support of non- woody plant parts  Leaf structure Modified leaves with various functions include: – tendrils of plants such as beans or grape – the spines of cacti – succulent leaves for water storage – leaves adapted to attract pollinators such as those in poinsettia – Bulbs for storage (onion)  Tendrils Spines Succulent Leaves Bracts Leaf Crops  Stems Functions – Movement of materials Water & minerals from roots to leaves Manufactured food from leaves to roots – Support leaves & reproductive structures – Food storage Typical Stem Cross Section (Dicot Stem) Helianthus annuus sun flower Epidermis Cortex A ring of vascular bundles Pith  VASCULAR TISSUE – XYLEM TISSUE – PHLOEM TISSUE – Found together in VASCULAR BUNDLES – Arise primarily from apical meristem – Arise secondarily from vascular cambium Epidermis Cortex Collenchyma Cortex Parenchyma Fibers- rigid support Functional Phloem Vascular Cambium - adds 2° xylem and 2° phloem Xylem  Xylem tissue Conducts water Provides mechanical support 2 types of xylem cells: – tracheids – vessel elements – dead at maturity  Phloem Sieve Cell – alive when functioning, but lacks a nucleus Companion Cell – alive, controls itself and the sieve cell Conducts sugars and other nutrients Phloem Monocot Stem – cross section  Vascular Cambium in Dicots Location: between primary xylem and phloem Produces secondary xylem and phloem Newest xylem is next to the cambium. Oldest xylem is in the center of stem Xylem accumulates over time Phloem is destroyed by the outward growth and must be replaced yearly – Not found in monocots  Wood Xylem tissue of a dicot stem Springwood - Large cells Rapid growth Summerwood - Small cells Slow growth Annual rings – Formed by the growth difference between springwood and summerwood – Usually one produced per year Summer Wood Spring Wood One Year’s Growth  Specialized Types of Stems Tubers – Food Storage Area – Short, thick underground stem – Example potato  Specialized Types of Stems Rhizomes – Underground stems that produce roots on the lower surface and extend leaves and flower shoots above ground – Examples Iris Lily of the Valley  Specialized Types of Stems Stolons – Stem that grows horizontally above the soil surface – Example Strawberries Stem Crops  Roots Functions – Anchor the plant – Absorb water & minerals – Store food – Propagate or reproduce some plants  Different Types of Roots Tap Root – One main root, no nodes – Continuation of the primary root – Ideal for anchorage – Storage area for food  Different Types of Roots Fibrous Root – Many finely branched secondary roots – Shallow roots cover a large area More efficient absorption of water & minerals Roots hold the soil to prevent erosion  Different Types of Roots Aerial Roots – Clinging air roots Short roots that grow horizontally from the stems Fasten the plant to a support – Absorptive air roots Absorb moisture from the air  EXTERNAL ANATOMY Root cap Region of cell division Region of elongation Region of differentiation or maturation  Cortex Vascular cylinder Dermal Ground Epidermis Vascular Zone of Root hair differentiation Zone of elongation Zone of cell Mitotic division cells (including apical meristem) 100 μm Root cap Root hairs: Extensions of the epidermis to increase surface area for water absorption  Internal Parts of Roots Much like those of stems, with phloem, cambium and xylem layers Phloem – Carries food down the plant Xylem – Carries water & minerals up to the stem Dicot root in Cross Section Monocot Root in Cross Section Other Root Types Root Crops  Flowers Function – Contain the sexual organs for the plant. – Produces fruit, which protects, nourishes and carries seeds. – Attracts insects for pollination.  Parts of the Flower Sepals – Outer covering of the flower bud – Protects the stamens and pistils when flower is in bud stage – Collectively known as the calyx  Parts of the Flower Petals – Brightly colored – Protects stamen & pistils – Attracts pollinating insects – Collectively called the corolla  Parts of the Flower: Stamen Male reproductive part – Anther Produces pollen – Filament Supports the anther  Parts of the Flower: Pistil Female reproductive part – Ovary Enlarged portion at base of pistil Produces ovules which develop into seeds – Stigma Holds the pollen grains  Parts of the Flower: Pistil Style – Connects the stigma with the ovary – Supports the stigma so that it can be pollinated Flower Structure - RECAP Male sex organs: Stamens, composed of anther – organ that produces pollen (male gametophyte) Female sex organs: The carpel Ovary is the enlarged basal portion of carpel that contains the ovules (female gametophyte) The stigma is the receptive portion of the carpel for pollen grains to adhere  The Seed Parts of a Seed Cotyledon – The first leaves of a plant Seed Coat – Outside covering of a seed Endosperm – Food storage tissue that nourishes the embryo Embryo – New plant developed after fertilization  Fruit A mature ovary, sometimes including other floral parts. Function: – Seed dispersal – Seed protection Fruits Anim Wate Wind al r Dispersal of Seeds Gravit Wind Force y  Node - stem Nodes area where a leaf and bud } are attached Internode Internode - stem area between nodes  Plant Meristems Perpetual embryonic regions (stem cells) Zones for cell division  Meristem Types 1. Apical growth in length. Primary growth 2. Lateral/Cambiums growth in diameter. Secondary growth  Apical Meristem Types 1. RAM – Root Apical Meristem: primary growth of roots 2. SAM – Shoot Apical Meristem: primary growth of shoots  RAM Located at the tip of each growing root. Protected from the soil by the Root Cap. RAM Shoot apical meristem