Anatomy of Root in plants: Anatomy of Flowering Plants complete notes #biology #pgtbiology #kvs #nvs #emrs

STRUCTURE OF ROOT

The overall structure of the root comprises of, the zones of division, elongation, and maturation

The root is organised into three main regions

Region of Division

Region of Elongation

Region of Maturation

1.Zone of Division (RAM):

  • Apical meristems are the sites of primary growth. Apical meristems are zones of active cell division. Comprises of a zone of slow division: Quiescent Centre.
  • It is subterminal in position.
  • Protected by a Root cap, In the Root cap a specialized region called as Columella sense gravity (Gravisensing) due to large amount of amyloplast.
  • Amyloplast of columella also do refer to as Statoliths meaning static rock and statolith containing cells are called as Staocytes.
  • It generates cells of both the root cap and the root.
  • It produces the protoderm, ground meristem, and procambium, which are active in the so-called zone of division.
  • Meristemoids: The are Small superficial cluster of cells that give rise to trichomes and Stomata.

2.Zone of Elongation:

  • The elongation zone is the site of rapid and extensive cell elongation. Although some cells continue to divide while they elongate within this zone, the rate of division decreases progressively to zero with increasing distance from the meristem.
  • Cells in this zone undergo elongation prior to full differentiation.
  • This elongation is responsible for an increase in length of the root.

3.Zone of Maturation:

  • The maturation zone is the region in which cells acquire their differentiated characteristics. Cells enter the maturation zone after division and elongation have ceased.
  • In this region lateral organs such as lateral roots and root hairs may begin to form. Differentiation may begin much earlier, but cells do not achieve their mature state until they reach this zone.

Anatomy of Dicot Root

Epiblema:

  • It is derived from Protoderm. The outermost layer is epiblema. Many of the cells of epiblema protrude in the form of unicellular root hairs.
  • Epiblema can be multilayered as in aerial roots of orchid.It lacks the cuticle and stomata.

Cortex:

  • It is derived from ground meristem.
  • The cortex consists of several layers of thin-walled parenchyma cells with intercellular spaces.
  • Its role is in storage.

Endodermis:

  • The innermost layer of the cortex is called endodermis.
  • It comprises a single layer of barrel shaped cells without any intercellular spaces.
  • The tangential as well as radial walls(side) of the endodermal cells have a deposition of water-impermeable, waxy material suberin in the form of Casparian strips.
  • Due to Casparian thickenings the passage shifts from apoplast to Symplast
  • Act as a Biological Check point.
  • Development of Root Pressure.

  • It prevents the free flow of material between individual cells and forces the material to cross the plasma membrane for a Biological Check so that only ions and minerals can pass across endodermis.

    This selective movement of osmolytes through endodermis to xylem develops a root pressure. Because the osmolytes bind with water and hence decrease the water potential of xylem so that xylem can draw extra water to xylem.

    Xylem water is under tension during transpiration when evaporation at leaves pulls water from leaves.

    Xylem is under Pressure when root pressure is developed by endodermis.

    Root pressure is responsible for the phenomenon of guttation, the forcing of water out of leaf hydathodes

Pericycle:

  • Next to endodermis lies a few layers of thick-walled parenchymatous cells referred to as pericycle.
  • Its main function is Initiation of lateral roots and vascular cambium formation during the secondary growth

Vascular Tissue:

  • The central vascular cylinder of the root is called the stele
  • Xylem and Phloem are present in form of patches. There are usually two to four xylem and phloem patches.
  • The entire central part of root is covered by xylem with radiating arms so there is solid cylinder of xylem in the middle with phloem to the exterior.
  • The radiating arms of xylem or Xylem poles are two to many in number.
  • Dicots typically have discrete xylem poles. A two-arm pattern is called diarch, followed by triarch, tetrarch, pentarch
  • The steles are Protostele, having central xylem surrounded by a ring of phloem.
  • Larger Monocot roots have a polyarch with so many xylem poles that they may be called an atactostele.
  • Monocot and eudicot roots both have an exarch pattern of vascular development with protoxylem to the exterior and metaxylem to the interior            
Which of the following summarize the role of Casparian strips in transport of water in the roots? (KVS PGT Biology)
Symplast to Apoplast 
Apoplast to Symplast
Phloem to Xylem
Xylem to Phloem

Unicellular elongation of epidermal cells are called as: (KVS PGT Biology)
Trichomes
Epidermal Hair
Epidermal Fibers
Root Hairs

Casparian strips helps in (NVS PGT Biology2019)
Development of Root pressure 
Turgidity of Tissue
Exchange of gases
Opening of stomata

Lateral root initiates from?
Root epidermis
Pericycle
Endodermis
Root Apical Meristem

In Angiosperms normally Exarch xylem occurs in (GATE-XL)
Dicot stem
Monocot Stem
Dicot Root
Dicot Leaf

Quiscent center is present in (GATE-XL)
Leaf Meristem
Root Apical Meristem
Shoot Apical Meristem
Floral Meristem

Distal part of Apical Meristem of Root is (GATE-XL)
Terminal in position
Subterminal in position
Lateral in position
Sublateral in position

Which one of the following organelle controlling gravitropism in root? (GATE-XL)
Chromoplast
Elaioplast
Amyloplast
Etioplast

A band of suberin layer develops all around the cell in the middle of the transverse and radial walls. This suberin is called ________ strip. (ICAR PG Crop Science)
1.Intercalary 
2. Pericycle
3. Cambium 
4. Casparian

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