PLANT ANATOMY AND PLANT PHYSIOLOGY

PLANT ANATOMYAND PLANT PHYSIOLOGYLearning ObjectivesAt the end of this lesson the students will be able to: Understand vascular tissue system- their types and functions. Know the structure of dicot root, stem, leaf and monocot root, stem, leaf. Differentiate the internal structure of dicot root, stem, leaf with that of monocot root,stem, leaf. Name the different pigments found in chloroplast. Elaborate on the structure and functions of plastids. Enumerate the steps involved in photosynthesis. Understand the structure of mitochondria List the basic events of aerobic and anerobic respiration.can be broadly classified into two, based ontheir ability to divide. They areIntroductionPlants exhibits varying degrees oforganization. Atoms are organized intomolecules, molecules into organelles, organellesinto cells, cells into tissues and tissues intoorgans. The first account of internal structureof plants was published by English PhysicianNehemiah Grew. He is known as Father ofPlant Anatomy. Plant anatomy (Gk Ana asunder; Temnein to cut) is the study of internalstructure of plants. You have already studied thedifferent kinds of tissues in IX standard. In thislesson, you will study about the internal structureof plant tissues, process of photosynthesis andrespiration.i) Meristamatic tissueii) Permanent tissue.12.2 Tissue systemSachs (1875) classified tissue system inplants into three typesi) Dermal or Epidermal tissue systemii) Ground tissue systemiii) Vascular tissue systemThe functions of these tissues are given inTable 12.1.12.2.1 Dermal or EpidermalTissue System12.1   TissuesTissues are the group of cells that aresimilar or dissimilar in structure and origin,but perform similar function. Plant tissuesIt consists of epidermis, stomata andepidermal outgrowths. Epidermis is the outer mostlayer. It has many minute pores called stomata.17310th Science Unit-12.indd 17321-02-2019 18:41:31

Table 12.1 Tissue system and its functionsTissue SystemDermal Tissue SystemGround Tissue SystemVascular Tissue SystemComponentsFuntionsEpidermis and Periderm(in older stems and roots) Protection Prevention of water lossParenchyma tissue Collenchyma tissueSclerenchyma tissuePhotosynthesisFood storageRegenerationSupportProtection Transport of water andminerals Transport of foodVascular tissues- Xylem tissue- Phloem tissueCuticle is present on the outer wall of epidermis tocheck evaporation of water. Trichomes and roothairs are the epidermal outgrowths.(ii) Conjoint bundlesFunctions:a) Collaterali)Xylem lies towards the centre and phloemlies towards the periphery.Xylem and phloem lie on the same radius.There are two types of conjoint bundles.Epidermis protects the inner tissues.ii) Stomata helps in transpiration.When cambium is present in collateralbundles, it is called open. e.g. dicot stem andcollateral bundle without cambium is calledclosed. e.g. monocot stem.iii) Root hairs help in absorption of water andminerals.12.2.2 Ground Tissue SystemIt includes all the tissues of the plantbody except epidermal and vascular tissueslike (i) Cortex (ii) Endodermis (iii) Pericycle(iv) Pithb) Bicollateral12.2.3 Vascular Tissue System(iii) Concentric BundlesIt consists of xylem and phloem tissues.They are present in the form of bundles calledvascular bundles. Xylem conducts water andminarals to different parts of the plant. Phloemconducts food materials to different parts ofthe plant.Vascular bundle in which xylem completelysurrounds the phloem or viceversa is calledconcentric vascular bundle. It is of two types:In this type of bundle, the phloem ispresent on both outer and inner side of xylem.e.g. Cucurbita1. Amphivasal: Xylem surrounds phloem.e.g. Dracaena2. A mphicribral: Phloem surrounds xylem.e.g. FernsThere are three different types of vascularbundles namely (i) Radial (ii) Conjoint(iii) Concentric(i) Radial BundlesEndarch: Protoxylem lies towards the centreand metaxylem lies towards the periphery. e.g.stem.Xylem and phloem are present in differentradii alternating with each other. e.g. rootsExarch : Protoxylem lies towards the peripheryand metaxylem lies towards the centre. e.g. roots.10th Standard Science10th Science Unit-12.indd 17417421-02-2019 18:41:31

PhloemCambiumXylemXylemPhloemRadialConjoint, collateral and openConjoint, collateral and closedOuter PhloemOuter CambiumXylemXylemPhloemInner CambiumInner PhloemConjoint, BicollateralConcentric and AmphicribralConcentric and AmphivasalFigure 12.1 Types of vascular bundle(a) Pericycle: Inner to endodermis lies asingle layer of pericycle. It is the site of originof lateral roots.12.3   Internal Structure ofDicot Root (Bean)A thin transverse section of dicot rootshows the following structures.(b) Vascular bundle: It is radial.Xylem is exarch and tetrach. The tissuepresent between xylem and phloem is calledconjunctive tissue. In dicot root, it is made upof parenchyma.(i) Epiblema: It is the outermost layer.Cuticle and stomata are absent. Unicellularroot hairs are present. It is also known asRhizodermis or Piliferous layer.(c) Pith: Young root contains pith whereasin old root pith is absent.(ii) Cortex: It is a multilayered large zonemade of thin-walled parenchymatous cellswith intercellular spaces. It stores food andwater.12.4   Internal Structure ofMonocot Root (Maize)(iii) Endodermis: It is the innermost layerof cortex. The cells are barrel - shaped, closelypacked, and show band like thickenings ontheir radial and inner tangential walls calledcasparian strips. It helps in the movement ofwater and dissolved salts from cortex into xylem.A thin transverse section of monocotroot, shows the following characteristicfeatures.i. Epiblema or Rhizodermis: It is theoutermost layer of the root, and is made upof single layer of thin walled, parenchymatouscell. Stomata and cuticle are absent. The roothair helps in absorption of water and minerals(iv) Stele: All tissues inner to endodermisconstitute stele. It includes pericycle andvascular bundle.17510th Science Unit-12.indd 175Plant Anatomy and Plant Physiology21-02-2019 18:41:31

Root hairPiliferous layerCortexRoot hairPiliferous layerCortexPhloemEndodermisXylemPithGround planGround planRoot hairRoot hairPiliferous layerPiliferous layerCortexCortexEndodermisPhloemCasparian asparian stripPithA sector enlargedA sector enlargedFigure 12.2 Transverse section of Dicot rootFigure 12.3 Transverse section ofMonocot rootfrom the soil. This layer also protects the innertissues.c) Pith: It is present at the center. It is made upof parenchyma cells with intercellular spaces.It contains abundant amount of starch grains.It stores food.ii. Cortex: It is multilayered large zone,composed of parenchymatous cells withintercellular spaces. It stores water and foodmaterial.iii. Endodermis: It is the innermost layerof cortex with characteristic casparian stripsand passage cells. Casparian strips are bandlike thickening made of suberin.12.5   Internal Structure of DicotStem (Sunflower)The transverse section of a dicot stemreveals the following structures.iv. Stele: All the tissues inner toendodermis constitute stele. It includespericycle, vascular tissues and pith.a) Pericycle: It is a single layer of thin walledcells. The lateral roots originate from this layer.b) Vascular tissues: It consists of many patchesof xylem and phloem arranged radially. Thexylem is exarch and polyarch. The conjunctivetissue is made up of sclerenchyma.10th Standard Science10th Science Unit-12.indd 1761. Epidermis: It is the outermost layer. It ismade up of single layer of parenchymacells, its outer wall is covered with cuticle.It is protective in function.2. Cortex:- It is divided into three regions:(i) Hypodermis: It consists of 3 - 6 layersof collenchyma cells. It gives mechanicalsupport.17621-02-2019 18:41:31

Table 12.2 Differences between Dicot and Monocot rootS. No. TissuesDicot RootMonocot Root1Number of XylemTetrarchPolyarch2CambiumPresent(During secondarygrowth only)Absent3Secondary GrowthPresentAbsent4PithAbsentPresentcells. It is covered with thick cuticle.Multicellular hairs are absent and stomataare also less in number.(ii) Middle cortex: It is made up of fewlayers of chlorenchyma cells. It is involedin photosynthesis due to the presence ofchloroplast.2. Hypodermis: It is made up of few layersof sclerenchyma cells interrupted bychlorenchyma. Sclerenchyma providesmechanical support to plant.(iii) Inner cortex: It is made up of fewlayers of parenchyma cells. It helps in gaseousexchange and stores food materials.3. Ground tissue: The entire mass ofparenchyma cells next to hypodermisEndodermis is the inner most layer ofcortex it consists of a single layer of barrelshaped cells, these cells contain starch grains.So it is also called starch sheath.Epidermal hairEpidermisHypodermisCortexEndodermis3. Stele: The central part of the stem inner toendodermis is known as stele. It consists ofpericycle, vascular bundle and pith.(i) Pericycle: It occurs between vascularbundle and endodermis. It is multilayered,parenchymatous with alternating patches ofsclerenchyma.Vascular bundlePithGround planEpidermal hairCuticle(ii) Vascular bundle: Vascular bundlesare conjoint, collateral, endarch and open.They are arranged in the form of a ring aroundthe i) Pith: The large central parenchymatouszone with intercellular spaces is called pith. Ithelps in the storage of food materials.EndodermisPhloemCambium12.6   Internal Structure ofMonocot Stem (Maize)XylemPithA transverse section of monocot stemreveals the following structures.A sector enlarged1. Epidermis: It is the outermost layer. It ismade up of single layer of parenchymaFigure 12.4 Transverse section of Dicot stem17710th Science Unit-12.indd 177Plant Anatomy and Plant Physiology21-02-2019 18:41:32

and extending to the centre is calledground tissue. It is not differentiated intoendodermis, cortex, pericycle and pith.EpidermisGround tissueVascular bundles4. Vascular Bundle: Vascular bundles are skullshaped and scattered in the ground tissue.Vascular bundles are conjoint, collateral,endarch and closed. Each vascular bundleis surrounded by few layer of sclerenchymacells called bundle sheath.Ground planCuticleEpidermisHypodermisChlorenchyma(a)   Xylem: It consists of metaxylem andprotoxylem. Xylem vessels are arrangedin V or Y shape. In mature vascularbundle, the lower most protoxylemdisintegrates and form a cavity. This iscalled protoxylem lacuna.Vascular bundlesGround tissuePhloemMetaxylemProtoxylem(b)   Phloem: It consists of sieve tubeelements and companion cells. Phloemparenchyma, and phloem fibers areabsent.Bundle sheathA sector enlarged5. Pith: Pith is not differentiated in monocotstems.Figure 12.5 Transverse section ofMonocot stemTable 12.3 Differences between Dicot and Monocot StemS. No. Tissues1Hypodermis2Ground tissueDicot StemMonocot StemCollenchymatousDifferentiated into cortex,endodermis, pericycle and pith(i) Less in number(ii) Uniform in sizeSclerenchymatousUndifferentiated3Vascular bundles4Secondary growthPresent(i) Numerous(ii) Smaller near periphery, biggerin the centre(iii) Scattered(iv) Closed(v) Bundle sheath presentMostly absent5PithPresentAbsent6Medullary raysPresentAbsent(iii) Arranged in a ring(iv) Open(v) Bundle sheath absent(i) Upper epidermis: This is the outermost layermade of single layered parenchymatouscells without intercellular spaces. The outerwall of the cells are cuticularized. Stomataare less in number.12.7   Internal Structure ofDicot or Dorsiventral Leaf(Mango)The transverse section of leaf shows thefollowing structures.10th Standard Science10th Science Unit-12.indd 17817821-02-2019 18:41:32