Plant Biology - Roots - Quick Guides | Biology

Preview (5 of 15 Pages)

100%

Plant Biology - Roots - Page 1 preview image

Loading page ...

Study GuidePlant Biology–Roots1. Primary Root Tissues and StructureTheprimary roothas a simpler tissue arrangement than theprimary stem. This is because roots donot produce leaves, so they do not need side connections to the vascular system. As a result, theirinternal structure is more straightforward.Theprimary plant bodyof the root is formed by three primary meristems and has three mainregions:1.Epidermis–the outer protective layer2.Cortex–a broad middle region mainly for storage3.Stele (vascular cylinder)–the central conducting region1.1EpidermisTheepidermisis the outermost layer of the root. In young roots, many epidermal cells formroothairs.Why root hairs are important:•They greatlyincrease surface area•This allows morewater and mineral absorption•Each root hair is an extension of theprotoplast(living cell content)Root hairs:•Havevery thin walls•Areextremely delicateand easily broken•Live only for a short timeIn some plants, the root epidermis is covered by athin waxy cuticle. This layer is not thick enough toblock the movement of water and dissolved substances into the root.

Plant Biology - Roots - Page 2 preview image

Loading page ...

Study Guide1.2CortexThecortexlies between the epidermis and the stele and makes up thelargest portionof the primaryroot. It is composed mainly ofparenchyma cells.In manydicots (eudicots)andgymnospermsthat later develop extensive secondary growth, thecortex is eventuallycrushed, and its storage role is taken over by other tissues.The cortex hasthree distinct layers:1.Hypodermis (exodermis)2.Storage parenchyma3.Endodermis1.3Hypodermis (Exodermis)Thehypodermislies just beneath the epidermis and is usuallyone or two cell layers thick.Key features:•Cell walls areheavily suberized•Walls areimpermeable to water•Cells aretightly packedwith no air spacesFunctions:•Preventsloss of water and nutrientsfrom the cortex•Protects againstsoil microorganisms•Especially well developed inarid-region plantsand plants withshallow roots1.4EndodermisTheendodermisis theinnermost layer of the cortexand is easy to recognize because of specialstructures calledCasparian strips.Casparian strips:•Are bands ofsuberin•Occur on theradial and transverse walls•Block movement through cell walls

Plant Biology - Roots - Page 3 preview image

Loading page ...

Study GuideWhy this matters:•Water and dissolved minerals must passthrough living cell membranes•This allowsselective absorption•Harmful substances in the soil are prevented from entering the plantThe endodermis is:•Almost always present in roots•Rarely found in stems1.5Storage ParenchymaThestorage parenchymamakes up most of the cortex.Characteristics:•Thin-walled, living cells•Loosely packed withmany air spaces•Storestarch and other substancesFunctions:•Food storage•Providesaeration, allowing roots to get oxygen•Cells expand and shrink as materials move in and out1.6Stele (Vascular Cylinder)Thesteleincludes all tissuesinside the cortex, namely:•Pericycle•Xylem•Phloem•Pith(in some plants)In mostdicot roots, the center is filled withsolid xylem.In mostmonocot roots, the center contains aparenchymatous pith.

Plant Biology - Roots - Page 4 preview image

Loading page ...

Study Guide1.7PericycleThepericycleis a thin layer of parenchyma cells located justinside the endodermis.Important roles:•Cellsretain the ability to divide•Gives rise tolateral (branch) roots•During secondary growth, it forms:oVascular cambiumoOften thefirst cork cambiumThe pericycle can also produce more pericycle cells through division.1.8Vascular TissuesThe arrangement ofxylem and phloemdiffers between plant groups:•Dicot (eudicot) rootsoCentral, lobedxylem coreoPhloemlocated between xylem armsoThis arrangement is called aprotostele•Monocot rootsoXylem forms a ringoSurrounds a centralpithoThis arrangement is called asiphonosteleThese vascular patterns are important because they help scientiststrace evolutionary relationshipsamong plants.

Plant Biology - Roots - Page 5 preview image

Loading page ...

Study GuideSummary•Roots have asimpler structurethan stems•The cortex is mainly forstorage and regulation•The endodermis ensuresselective absorption•The pericycle formslateral roots•Xylem and phloem arrangement differs in dicots and monocotsThis organized structure allows roots toabsorb, store, regulate, and transportmaterials efficientlywhile anchoring the plant firmly in the soil2. Secondary Growth of Roots2.1What Is Secondary Growth in Roots?Secondary growth is the process thatincreases the thickness (girth)of roots.It is especially important inwoody perennial plants, where secondary tissues make upmost of theroot mass.•Primary tissuescontinue to form only in young feeder roots.•Themain supporting root systemis made ofsecondary tissues.•These tissues are produced bylateral meristems:oVascular cambiumoOne or more cork cambiaAlthough roots grow underground and are not easily seen, they areas massive as the aerial partsof trees.They balance the weight of the plant above the ground andkeep the tree upright and stable.

Preview Mode

This document has 15 pages. Sign in to access the full document!

Report

Plant Biology - Roots

Study Now!

Document Details

Related Documents

Plant Biology - Tissues

Plant Biology - Themes of Plant Biology

Plant Biology - The Shoot System Stems

Plant Biology - The Shoot System Leaves

Plant Biology - The Shoot System Flowers, Fruits, Seeds

Plant Biology - Systematics

Plant Biology - Seedless Vascular Plants

Plant Biology - Seed Plants

Plant Biology - Respiration

Plant Biology - Protista

Company

Explore

Study Tools