Tag: evs

Roots are the part of the plant that lies below the soil surface. It is an important part of a plant and plays many major roles such as acting as an anchor for the plant. Since it lies in the soil, it also absorbs and transports nutrients and water from the soil. It also prevents soil erosion.

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.

Velamen is a spongy, multiple epidermis that covers the roots of some epiphytic or semi-epiphytic plants, such as orchid and Clivia species. The velamen of an orchid is the white or gray covering of aerial roots. When dry and usually more green when wet as a result of the appearance of underlying photosynthetic structures. It is many cell layers thick and capable of absorbing atmospheric moisture and nutrients. Often, the roots of orchids are associated with symbiotic fungi or bacteria, the latter may fix nutrients from the air. So, velamen is meant for absorption of water from air and not for absorption of water from host, perennation or protection.

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 :