Botany and Plant Science

Water is absorbed by land plants through their roots especially at their tips the root hairs found in large number in this region increase the surface area of absorption. The concentration of soil water is less than of cell sap of root hair as a result the soil water enters the root hair by endosmosis.

The three principal tissues of the root vascular cylinder, cortex and epidermis originate from three groups of initial cells or histogens, in the apical meristem plerome, periblem and dermatogen respectively. A fourth histogen, the calyptrogen produces the root cap.        
So, the correct answer is 'root cap'

The adventitious roots found in the epiphytes are known as the epiphytic root. These roots hang freely in the air and absorb the moisture from the air by a special type of tissue called as velamen. Epiphytic plants are sometimes called as air plants because they do not have roots in the soil. For example, Vanda.

In plants like Arceuthobium, Rajflesia, Sapria, Podostemon, shoot develops for flowering otherwise roots form main part of the plant.

Passage cells are endodermal cells of older monocot roots, which have retained thin walls and casparian strips. They are not suberized and waterproof. They allow symplastic flow of solutes, such as calcium and magnesium into the stele.

Calyptrogen is a histogen which produces the root cap.
Thus, the correct answer is option A.

The thick waxy layer covers the surface of aerial organs is termed as Cuticle. It is composed of a waxy substance called cutin. It is thin in mesophytes and extremely thick in xerophytes. The cuticle is absent in hydrophytes and underground organs and young roots. Other three options the bearing Cuticle.

So, the correct option is 'Young roots'.

The correct option is B.

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

• The quiescent centre is that part of the root-promeristems that contains the initials of epidermis, cortex and stele.
  
• These cells divide less frequently as they are inactive and are present at the pole of cortex and stele.
  
• The cells with QC have small dictyosomes, nuclei and nucleoli with little cytoplasm.
  
• These cells also have little endoplasmic reticulum, mitochondria and contain low concentrations of RNA, DNA and protein than the other cells of the root apex.
  
• So, the correct answer is 'Little meristematic activity'.

The radial walls of the endodermis are marked by characteristic thickenings, called the casparian strips. These thickenings contain lignin, suberin and phenolic oxidation products that gives the strips a dark colour. The endodermis is a typical cell layer of roots. In roots, it is localized at the periphery of the vascular cylinder. 

This region represents the zone of differentiation or maturation because different types of primary tissues differtiate or mature in this region. Root hair zone is 1 - 6 cm in length. Most of the water absorption occurs in this region. Some of the outer cells of this zone give rise to lateral tubular outgrowths called root hairs. The root hairs increase the exposed surface of the root for absorption.

Root consist of four parts:-

1.  Root cap which protects the root and secrete mucilage which lubricates the root.
   
2. Region of meristematic activity where apical meristem is present and increase the length of root.
3. Region of elongation where the newly-formed cells increase in length, thereby lengthening the root.
4. Region of maturation that bears unicellular root hairs which increases the surface area and helps in the absorption of water.