Botany and Plant Science

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'.

Pericycle is the region consisting of one or more layers of cells, found external to central cylinder (stele). Pericycle is composed of parenchyma cells or sclerenchyma cells or both. Lateral branches and phellogen arise from pericycle.

• 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.

So, the correct option is 'Cell maturation'.

In underground stem axillary buds are present at the axil of scale leaves, roots do not give rise to buds-therefore incorrect.Flowers and fruits may be present in some underground stem (example Commelina). However, fruits and flowers are absent in roots - therefore statement incorrect. Underground stem usually perform the function of food storage (example- ginger, potato), however roots are meant to be underground, their primary function being absorption of water and minerals, only in certain cases they store food(sweet potato, carrot).

The root hairs of  plants are actually tubular outgrowth of trichoblast, a hair-forming cell present on the epidermis of roots. These help the plants to increase the surface area of their roots so as to absorb the mineral nutrients present in the soil. In most dicotyledons and monocots, the root hairs are unicellular, thin walled and un-branched  structures and are short lived. However, there are exceptions such as the ones found in the aerial adventitious roots of Kalanchoe where these are multicellular.

A typical root has four regions. 

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. 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. This functionality allows the orchid to exist in locations that provide a reproductive or vegetative advantage such as improved exposure or reduced competition from other plant species. The velamen also serves a mechanical function, protecting the vascular tissues in the root cortex, shielding the root from transpirational water loss and, in many cases, adhering the plant to the substrate. Velamen is not found in breathing roots of halophytes, parasitic plants and all aerial roots. The typical orchid root has a stele of comparatively small diameter. It is surrounded by a cortex which is further enveloped by a highly specialized exodermis, most of which at maturity do not contain protoplasm. A few cells, however, are living and allow the passage of water through them. The exodermis is surrounded by velamen, consisting of one to several layers of cells, which can develop root hair under proper environmental conditions. 

Many plants growing in aquatic habitats do not possess roots because there is little requirement for absorption of water and mineral salts, e.g., Wolffia, Utricularia, Myriophyllum, Ceratophyllum. In other aquatic plants, roots develop only for balancing (e.g., Lemna, Pistia) and fixation (e.g., Hydrilla). The root cap is a section of tissue at the tip of a plant root. It is also called as calyptra. Root caps contain statocytes which are involved in gravity perception in plants. If the cap is carefully removed the root will grow randomly. The root cap protects the growing tip in plants. It secretes mucilage to ease the movement of the root through soil and may also be involved in communication with the soil microbiota. Since, roots in Pistia are only for balancing, root cap is not required. So, root cap is absent in Pistia. 

The thick waxy layer covers  the surface of aerial organs is called Cuticle. It is made up of waxy substance called cutin. It is thin in mesophytes and highly thick in xerophytes. It is absent in hydrophytes and underground organs.

A. Dermatogen is the primary meristem that forms the outermost layer of a plant or a plant part and forms the epidermis.

B. Calyptrogen is a specialized layer of rapidly dividing cells present at the root tips which continuously divide to form the root cap is formed.

C. Wound cambium is formed within amasses of cells (callus) which grow over the injured surface of a wound to heal and repair that part.

D. Vascular cambium is a lateral meristem that develops within the vascular bundles to produce xylem to the inner side and phloem to the outer side and is also called fascicular cambium.

So, the correct answer is A.