Dicot and Monocot Root PDF

Unit - III The Root - Primary structure of dicot root and monocot root Rev. Dr G Victor Roch SJ Roots Roots are the important underground part of all vascular plants. This part of the plant is mainly responsible for anchoring it down into the ground and...

Unit - III The Root - Primary structure of dicot root and monocot root Rev. Dr G Victor Roch SJ Roots Roots are the important underground part of all vascular plants. This part of the plant is mainly responsible for anchoring it down into the ground and absorbing the essential mineral elements, nutrients, and water from the soil. It is also used to store food. However, not all plants have their roots underground, some plants have their roots growing above the ground. These are called aerial roots. Alike underground roots, these aerial roots (Banyan Tree, Mangroves, etc.) also responsible for absorbing nutrients, anchoring and affixing the plant by supporting them to the structures such as nearby walls, rocks, etc. Functions of Root Roots perform various functions that are necessary for the survival of the plants. They are an integral or integrated system that helps the plant in:  Anchoring: Roots are the reason plants remain attached to the ground. They support the plant body, ensuring that it stands erect.  Absorption: Primary function of the roots is to absorb water and dissolved minerals from the soil. This is crucial as it helps in the process of photosynthesis.  Storage: Plants prepare food and store in the form of starch in the leaves, shoots and roots. Prominent examples include carrots, radish, beetroot, etc.  Reproduction: Even though roots are not the reproductive part of plants, they are vegetative parts. In some plants, the roots are a means of reproduction. For instance, new plants arise from creeping horizontal stems called runners (stolons) in jasmine, grass, etc. This type of reproduction is called vegetative propagation.  Ecological Function: They check soil erosion, provide sustenance and also habitat to various organisms. I. T.S of Dicot Root – Cicer Root The T.S of dicot root shows the following structures: (Pea, beans, peanuts, etc.) 1. Epiblema or Epidermis Epidermis are of densely arranged cells with thin cell walls forming the Epidermis outermost single layer. Several cells have thin outgrowths known as root hairs. 2. Cortex It is present under the epidermis consisting of several layers of thin-walled parenchyma cells. The cortex is comparatively narrower than the monocot root. 3. Endodermis They are barrel-shaped forming the innermost layer of the cortex. They are densely arranged single layer. A Casparian band is formed due to the radially arranged cell walls that are thickened and prominent. 4. Pericycle Under the endodermis is a thin-walled layer of cells known as pericycle. Conjunctive tissue It forms cock cambium and lateral roots. A section enlarged 5. Vascular bundles ▪ It consists of radial bundles having alternating 2 to 6 arrangement of bundles of phloem and xylem. Usually the xylem is tetrarch. ▪ Bundles of xylem are exarch wherein the metaxylem is Epidermis present towards the center and the protoxylem at the outer side. ▪ In outline, xylem vessels are polygonal. 6. Phloem bundles ▪ Comprises of companion cells, parenchyma and sieve tube. 7. Conjunctive tissue ▪ They are the parenchyma and sclerenchyma cells that separate the xylem and phloem bundles from each other. ▪ Cambium is present formed by conjunctive parenchyma tissue. Conjunctive tissue 8. Pith ▪ They are significantly absent or occur rarely and less developed. A section enlarged Salient features of Dicot Root The epidermis shows the presence of unicellular hair. Absence of hypodermis. Radially arranged vascular bundles. The number of phloem/xylem bundles is not more than 6. The xylem is an exarch. Absence or rare occurrence of pith. Cambium is present and hence the secondary growth occurs in dicot root. II. T.S of Monocot Root – Canna Root The T.S of monocot root shows the following structures: (Maize, banana, palm, etc.) 1. Epiblema or Epidermis ▫ It is a single outermost layer with no cuticle. ▫ Densely arranged cells. ▫ Few cells may see unicellular root hair emerging. 2. Cortex ▫ Found below epidermis. ▫ It is broad consisting of multiple layers of parenchyma cells. 3. Endodermis ▫ The innermost layer of the cortex. ▫ Barrel-shaped cells arranged in a ring-like manner. ▫ Presence of less prominent Casparian bands. 4. Pericycle Conjunctive tissue ▫ Found below the endodermis and is a single layer of parenchymatous cells. ▫ It forms lateral roots only. 5. Vascular bundles ▪ There are 8 or more alternating bundles of phloem and xylem known as radial bundles. ▪ Xylem bundles are exarch and polyarch. ▪ Xylem bundles are oval or rounded. ▪ Phloem is found under the pericycle and comprises of companion cells, sieve tube, parenchyma 6. Conjunctive tissue ▪ It is the xylem and phloem bundles that are distinguished from each other by the parenchyma tissue. 7. Pith Conjunctive tissue ▪ Well developed and prominent pith is observed. ▪ It comprises of the parenchyma in the mid-region of the root. Salient Features of Monocot Root ▪ Epidermis has the presence of unicellular hair. ▪ Absence of hypodermis. ▪ Radially arranged vascular bundles. ▪ 8 or more than 8 phloem and xylem bundles. ▪ The xylem is an exarch and polyarch. ▪ A well-developed pith. ▪ Cambium is absent and hence there is no secondary growth occurs in monocot root.