Internal structure of monocot root - class-XI

Monocot roots differ from dicot roots by having a large, well-developed pith (c) and a polyarch xylem arrangement. The cortex is parenchymatous (d), and the pericycle (a) is also parenchymatous.

 In dicot stem, bundle sheath is absent, while in monocot stem the bundle sheath is present as it surrounds the scattered vascular bundles. So the correct option is 'Only (b) is incorrect'.

Dermatogen is the histogen or meristematic regions of root and stem which is produced by apical meristem and give rise to uniseriate epidermis by anticlinal divisions; option A is incorrect. Monocotyledons have one additional histogen along with dermatogens, periblem and plerome Calyptrogen being the fourth one that makes root cap. The vascular cambium, also called as wood cambium, has thin walled highly vacuolated cells of two types, the fusiform initials and the ray initials. The fusiform initials are the elongated cells that give rise to secondary xylem and secondary phloem. Ray initials are horizontally organized and produce vascular rays (medullary rays or ray parenchyma). 

Pith is the innermost region of the root representing the central axis. It is composed of few loosely arranged parenchyma cells. Large pith is present in monocot roots. In dicot roots, pith is absent. Open vascular bundles are present in dicots. Scattered vascular bundles are present in moncot stem. Radial vascular bundles are present in both monocot and dicot roots.

Monocot root vascular bundles are radial in arrangement. There are eight bundles each of xylem and phloem. Hence, the condition is described as polyarch. Xylem is described as exarch in them. 

The sequence of layers in typical monocot root from outer surface to inside is epiblema, cortex, endodermis, stele, pericycle, conjunctive tissue, pith and vascular bundles. Thus, option C is correct.

Passage cells are endodermal cells of older monocot roots which have retained thin walls and Casparian strips rather than becoming suberized and waterproof like the other cells around them, to continue to allow some symplastic flow to the inside. Experimental evidence suggests that passage cells function to allow transfer of solutes such as calcium and magnesium into the stele, in order to eventually reach the transpiration system. For the most part, however, old roots seal themselves off at the endodermis, and only serve as a passageway for water and minerals taken up by younger roots "downstream". Passage cells are absent in dicot roots, monocot stem and dicot stem.

Passage cells are endodermal cells of older roots which have retained thin walls and Casparian strips rather than becoming suberized and waterproof like the other cells around them, to continue to allow some symplastic flow to the inside. Passage cells function to allow transfer of solutes, such as calcium and magnesium into the stele, in order to eventually reach the transpiration system. 

In monocot root vascular bundles are radial in arrangement. There are eight bundles each of xylem and phloem. Hence, the condition is described as polyarch. Xylem is described as exarch in monocot root.

In mature monocot roots, after the loss of epidermis, the outer cells of general cortex are suberised become thick-walled layer called exodermis.

So, the correct option is ‘Monocot root’.

The anatomy of dicot root and monocot root more or less similar in majority of characters. They are epidermis, general cortex, endodermis, type of vascular bundles, nature of xylem.

a) Wrong – because in dicot root pericycle is meant for production of lateral roots and cambium whereas in monocot root it is pericycle is meant for lateral production only.

b) True – In dicot root stele is diarch to tetrarch, whereas in monocot root, stele is polyarchy.

c) True – In dicot root, cambium is developed laterally, whereas in monocot root, cambium is absent.

d) False – because, in dicot root is pith is poorly developed, whereas in monocot root pith is well developed.

So, the correct option is ‘a,d’.

A monocot root possesses polyarch (more than 4) condition of vascular bundle, here the vascular bundles are radial, closed with exarch condition of the xylem, embedded in the ground tissue that has a well developed central region or the pith or medulla.

Polyarch vascular bundle (more than 4)  is observed in monocot root. The vascular bundle is radial and closed, with exarch condition of the xylem. 

Statement (iii) is correct as sunflower stems have multicellular hairs (trichomes). Statement (iv) is correct as the central portion of a dicot stem is the pith. The other statements contain errors regarding the arrangement or terminology.

Well developed pith or parenchymatous central region is present in monocot root (maize) and dicot stem (Sunflower). Its a structure of loosely arrannged cells that embeds vascular tissue, it may store food.

Monocot root vascular bundles are radial in arrangement. There are eight bundles each of xylem and phloem. Hence, the condition is described as polyarch. Xylem is described as exarch in monocot root. 

Passage cells are endodermal cells of older roots, which have retained thin walls and Casparian strips rather than becoming suberized and waterproof like the other cells around them, to continue to allow some symplastic flow to the inside. 

Monocot root vascular bundles are radial in arrangement. There are eight bundles each of xylem and phloem. Hence, the condition is described as polyarch. Xylem is described as exarch. 

Development of xylem from the periphery to the centre is called centripetal xylem. It is found in roots.

So, the correct option is ‘root’.

Monocot root vascular bundles are radial in the arrangement. There are eight types of bundles each of xylem and phloem. Thus the condition is described as the polyarch. Xylem is detailed as an exarch.

Monocot stem vascular bundles are many in number and the xylem is the endarch.

Dicot stem vascular bundles are also eight in number but arranged in the form of a broken ring. The vascular bundles are conjoint, collateral and open. Xylem is on the inner surface and phloem on the outer surface. Xylem is described as an endarch.

Dicot root vascular bundles are described as radial and tetrarch. There are four bundles each of xylem and phloem occurring alternately. Xylem is described as an exarch.

So, the correct answer is 'Monocot root'

So, the correct answer is B.

A. Epiblema – root epidermis with root hairs is called epiblema

B. Pericycle – outer most part of the stele in roots and dicot stem, produces lateral branches

C. Cortex – middle of root and dicot stem internally

D. Endodermis – inner most part of the cortex

So, the correct option is ‘Pericycle'

Endodermal cells without casparian strips or bands are called passage cells. These are present opposite to the protoxylem cells. These are found in both dicot root and monocot root.

The anatomy of dicot root differs from monocot root, in activity of pericycle, no. of xylem strands, presence of medulla, activity of conjunctive tissue.  

In monocot root, the vascular bundles are usually more than six in number. Pith is large and parenchymatous. The parenchyma of the pith become lignified and sclerenchymatous.