Botany and Plant Science

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 exarch. Endodermis is present in dicot roots. Pith is absent in older dicot roots. 
Thus, the correct answer is option B.

According to histogen theory, as proposed by Hanstein, the root and shoot apices have three distinct meristematic regions called as histogens. These are namely; dermatogen, periblem and plerome. The dermatogens make uniseriate epidermis by anticlinal divisions, periblem forms cortex and plerome serve as the progenitor of stele (pericycle, vascular bundles, pith rays or medullary rays and pith). Monocotyledons have a fourth histogen, calyptrogen; being the fourth one, that makes root cap. 
Thus, the correct answer is option C.

According to histogen theory, as proposed by Hanstein, the root and shoot apices have three distinct meristematic regions called as histogens, these are namely dermatogens, periblem and plerome. The dermatogens makes uniseriate epidermis by anticlinal divisions, periblem forms cortex and plerome serve as progenitor of stele (pericycle, vascular bundles, pith rays or medullary rays and pith). Monocotyledons have four histogens; calyptrogen being the fourth one that makes root cap. 

Apex portion of root is made of protective tissue, root cap and the region of cell division is situated below the root cap. So, maximum growth in root occurs behind the apex and not in tips. Thus, option C is correct.

The pericycle is a cylinder of parenchyma or sclerenchyma cells that lies just inside the endodermis and is the outer most part of the stele of plants. Although, it is composed of non-vascular parenchyma cells, it is still considered part of the vascular cylinder because it arises from the procambium as do the vascular tissues it surrounds. In eudicots, it also has the capacity to produce lateral roots. Branch roots arise from this primary meristem tissue. In plants undergoing secondary growth, the pericycle contributes to the vascular cambium often diverging into a cork cambium. Cortex, pith and endodermis does not gives rise to lateral roots.
Thus, the correct answer is option A.

The pericycle is a cylinder of parenchyma or sclerenchyma cells that lies just inside the endodermis and is the outer most part of the stele of plants. Although, it is composed of non-vascular parenchyma cells, it is still considered part of the vascular cylinder because it arises from the procambium as do the vascular tissues it surrounds. In eudicots, it also has the capacity to produce lateral roots. Branch roots arise from this primary meristem tissue. In plants undergoing secondary growth, the pericycle contributes to the vascular cambium often diverging into a cork cambium. Thus, correct answer is option B.

The quiescent centre (QC) is a small group of cells with low mitotic activity. QC's are to be found at the tips of growing roots, in the root meristem and are typically surrounded by groups of initial cells. Through rounds of cell division, these initial cells give rise to the various tissues of the root and so there are usually vascular initials, pericycle initials, cortex initials etc. It is thought that the QC sends out signals to these initial cells to ensure that they remain in an initial state and keep dividing to produce whatever tissue they are responsible for. So, quiescent centre is found in root tips and not in shoot tip, floral tip or leaf tip. 
Thus, the correct answer is option A.

Lignification is associated with xylem. The lignin strengthens the walls of the xylem and the spirals provide flexibility. The advantages of lignification are :

The quiescent centre is a small group of cells with low mitotic activity (no cell division). Quiescent centre are to be found at the tips of growing roots, in the root meristem and are surrounded by groups of dividing cells.

The region of fastest growth is behind the root tip because it consists meristematic cell that has the ability to divide. It is 4-8 mm long portion behind the tip. This region is called as root elongation region.

The four zones from the root tip are root cap, cell division, cell enlargement, cell maturation. Each zone has primary meristematic tissues with different functions. Root cap has parenchyma at tip. Zone of cell division has apical meristem, where the cells divide every 12-36 hours. Zone of elongation or enlargement, where cells get longer. Zone of maturation, which become specific cell types like epidermal cells and cortex.