Morphology of the root - class-XI

Rema observed trichomes which are considered to be the outgrowth from the epidermis of the plant and are unicellular and mostly glandular. It helps in the absorption of water and minerals.

A)The root is covered at the apex by a thimble-like structure called the root cap that protects it from damage.

Quiscent centre is a zone of mitotically inactive zone in the meristematic region of the root apical meristem. The cells of this region either do not divide or divide very slowly. They have thin cytoplasm, low concentration of the RNA and proteins, fewer endoplasmic reticulum and dictyosomes. This zone acts as reservoir of meristematic cells. The cells ar ecapable of gaining the active dision activity at the time of growth.

Chloroplast are absent in root hairs because root hairs do not produce food. These are meant for absorption of water and minerals from soil. Chloroplast is the store house of chlorophyll which is the green pigment essential in photosynthesis.Moreover root and root hair are underground structures away from light, hence they do not contain chloroplasts, as chlorophyll pigments present within the chloroplasts are functional only in presence of light.

Screwpine or Pandanus also known as screw palm has stilt roots. Often called as Pandanus palms, these plants are not closely related to palm trees. The species vary in size from small shrubs less than 1 m. Species growing on exposed coastal headlands and along beaches have thick stilt roots- as anchors in the loose sand. Those prop roots emerge from the stem, usually close to but above the ground, which helps to keep the plants upright and secure them to the ground.
Thus, the correct answer is option C.

Asafoetida or hing is the dried latex (gum oleoresin) exuded from the rhizome or tap root of several species of Ferula, a perennial herb that grows 1 to 1.5 m tall. The species is native to the deserts of Iran, mountains of Afghanistan and is mainly cultivated in nearby India. Thus, option A is correct. 

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. 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. So, velamen tissues are associated with absorption of moisture and not with nutrition, assimilation and haustorial function.
Thus, the correct answer is option C.

In some plants, the roots are chlorophyllous and perform photosynthesis. For example, Tinospora, Taeniophyllm, Trapa, Podostemum.

Asafoetida is the dried latex (gum; oleoresin) exuded from the rhizome or tap root of several species of Ferula, a perennial herb that grows 1 to 1.5 m (35 ft) tall. It is also known as asant, food of the gods, jowani badian, stinking gum, Devil's dung, hing, ingu, kayam and ting.
Asafoetida is used for breathing problems including ongoing (chronic) bronchitis, H1N1 "swine" flu and asthma. It is also used for digestion problems including intestinal gas, upset stomach, irritable bowel syndrome (IBS), and irritable colon. Other uses include treatment of whooping cough (pertussis), croup and hoarse throat.
Some people use asafoetida for hysteria, insanity, convulsions and as a nerve stimulant for ongoing mental and physical fatigue with depression (neurasthenia).
Women sometimes use asafoetida to restart their menstrual periods after menstruation has stopped for some reason.
Asafoetida is sometimes applied directly to the skin for corns and calluses.
In manufacturing, asafoetida is used as a fragrance in cosmetics and as a flavoring ingredient in foods and beverages. Asafoetida is also used in products meant to repel dogs, cats and wildlife.

Roots form thorny branches in Acanthorhiza. Acanthorhiza has aerial roots which form thorny branches while terminating. Roots that are exposed to the atmosphere, at least during low tide, may be called as aerial or pneumatophores. Aerial roots are roots above the ground. They are almost always adventitious. They are found in diverse plant species, including epiphytes such as orchids, tropical coastal swamp trees such as mangroves.
Thus, the correct answer is option A.

Two kinds of root systems are present in flowering plants :
(i) Tap root : Primary root grows vertically down into soil, secondary roots grow from this at an acute angle outwards and downwards, and from these other branches may arise. The main or primary root is known as the tap root; together with its many branch roots it forms a tap root system e.g. the bean.
(ii) Adventitious root : The primary root usually dies at an early stage and is replaced by numerous roots that develop from the stem, e.g., the mealie.

Chicory (Cichorium intybus), is a somewhat woody, perennial herbaceous plant usually with bright blue flowers, rarely white or pink. Many varieties are cultivated for salad leaves, chicons (blanched buds) or for roots, which are baked, ground, and used as a coffee substitute and additive. 

A) Blue-green algae

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.

From the region of maturation in roots, the epidermis develops a special unicellular hair like structure known as root hairs that help to increase the surface area of root to maximize the absorption of water and minerals.

Plants can absorb nitrate or nitrite from the soil via their root hairs. If nitrate is absorbed, it is first reduced to nitrite ions and Ammonium ions for incorporation into various compounds.

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'

Pandanus has stilt roots with very large conspicuous aerial root cap. These are the largest and multiple persistent root caps.

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 external protective layer in dicot root is called as epiblema or piliferous layer. The cells of epidermis extend into unicellular root hairs. In the root cap there is no root hair present. In absence of root hairs water absorption is not possible. So, the correct answer is option B.

• 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.

The substance was named Cytokinin and it is involved in cell division and in the making of new plant organs, like a root or a shoot. Cytokinins are produced in the root apical meristems (very tip of the roots) and travel upward hitching a ride with water and traveling up the stem through the xylem.

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 roots of the plant Rauwolfia serpentina or sarpagandha is used to treat hypertension and mental disorders. The roots of the plant are dried to extract  the alkaloid resperine from the plant, which is used for medicinal purposes.

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. 

Inulin, is a levulosan which is found  among numerous angiosperm families. This carbodyhrate is found in the cell sap of some species, while in others it accumulates as an amorphous material. However, in some species this is form as inulin crystals and are found deposited in living tissues. This is found in colloidal condition in the roots of dahlia, artichoke and other members of Compositeae family. In Dahlia roots, the inulin depositions appear like fan like crystals.

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.