The root system - class-VII

The edible part of sweet potato is a modified adventures fleshy root which is called as tuberous root or single root tuber. Due to storage of food, the adventitious roots become thick and fleshly. In sweet potato, the swollen roots do not occur all over the tuber.

Red root is present in the plant beetroot. This is due to the presence of a substance named betacyanin which gives its color.

Stilt roots occur in sugarcane/Maize because these stems are weak and need support where adventitious roots grow from the nodes obliquely downwards towards the ground.

Roots do not show the distinction of nodes and internodes because the meristematic part of the roots is at the tip, but not in the middle showing differentiation. Roots have endogenous primary secondary and tertiary roots and rootlets.

A root cap is a protective covering over the tip of the root. Pandanus is known to have multiple roots because it has multiple prop roots covered with root caps.

Hygroscopic roots occur means water absorbing roots from the atmosphere. Hygroscopic roots occur in Vanda because it is an epiphyte which absorbs moisture from the atmosphere as its source of water.

Answer is option A i.e. "2,1,4,3"
Four zones in the root from apex to base are arranged in the sequence. Firstly, new root tips grow continuously throughout the life of the plant which is due to Meristematic zone. This in later growth phases provide the surfaces through which most of the nutrients and water move, hence followed by Mineral absorption zone and Water absorption zone and finally forming Maturation zone.

Regions of root from base to root tip are maturation zone , elongation zone and cell division zone and root cap because the meristematic tissue is present at the tip of the root above the root cap which grows downwards as the upper layers mature into permanent structures.

Origin of lateral roots is endogenous in origin because for absorption of water and minerals the roots should contain vascular structures which are in the deeper layers.

The main root of tap root system represents radicle because, in a seed, radicle is the part which is destined to produce where it grows and it produces branches from the main root.

A. Wolffia is a free-floating thallus, so its body does not contain roots.

Root hair the large thread like structure arises from the epidermis layer of the root. These basically arise from the region of elongation. Root hairs are rarely branched. These are exogenous in origin because arise from the superficial layer of the epidermis. Root hairs are unicellular.

Thus, the correct answer is 'False.'

They persist until the epidermis separates from the root, although hairs composed of living cells are usually found only on the tip 1 cm. of the roots. Hairs of adventitious roots growing in the soil are most commonly or always unicellular and look very much the same as hairs of many other roots.

Primary roots continue to grow to form a secondary root system as the secondary root system is large and extends deep into the ground.

Respiratory roots are non-photosynthetic and non-green in nature. They are seen in plants growing in marshy regions and in aquatic plants. They are found in wheat. They are also called as breathing roots. Fasciculated roots are modified adventitious roots. They are arranged in fascicles.

Some roots, called adventitious roots, arise from an organ other than the root—usually a stem, sometimes a leaf. They are especially numerous on underground stems, such as rhizomes, corms, and tubers, and make it possible to vegetatively propagate many plants from stem or leaf cuttings.

Root hairs are unicellular extensions of epidermal cells found in the zone of maturation, where they are responsible for water and mineral absorption.

Safranin is a common biological stain used to highlight cell walls and nuclei in plant tissue samples like onion root tips.

Roots exhibit negative phototropism, meaning they grow away from the light source, while stems exhibit positive phototropism.

The quiescent centre (QC) is a small group of cells with low mitotic activity (they divide sometimes, but only rarely). 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, root apex has a zone of slow dividing cells in the middle of rapidly dividing cells which is called as quiescent centre. 

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. Cork, epiblema and hypodermis are not capable of absorbing water from air. 
Thus, the correct answer is option B.

Plants absorb water through the entire surface using roots, stems and leaves. However, mainly the water is absorbed by roots. The area of young roots where most absorption takes place is the root hair zone. The root hairs are delicate structures which get continuously replaced by new ones at an average rate of 100 millions per day. The root hairs lack cuticle and provide a large surface area. They are extensions of the epidermal cells. They have sticky walls by which they adhere tightly to soil particles. As the root hairs are extremely thin and large in number, they provide enormous surface area for absorption. They take in water from the intervening spaces mainly by osmosis. So, most water absorption in plants takes place through root hair zone and not by root apex, root cap or meristematic zone.
Thus, the correct answer is option C.

Root xylem is exarch xylem in which xylem formed first is present towards the periphery and is termed as protoxylem while metaxylem is present near the centre. Exarch xylem refers to the presence of protoxylem and metaxylem in different radii, not in same. 

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.

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 :

Nymphaea, Sagittaria, Ceratophyllum and Vallesneria are hydrophytes, which grow in water. Nymphea, Sagittaria and Vallisnaria are rooted hydrophytes, while Ceratophyllum is a submerged floating hydrophyte. 

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.

When oxygen levels fall too low, the root cells respire anaerobically, producing ethanol (seedling only). Some marshy roots also respire anaerobically.

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

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.

1. Haustoria is the specialized structure present in parasitic  plant or fungus that absorbs water and nutrients. For example, Cuscuta.
2. Mycorrhizal roots are formed by the symbiotic association of plant roots and fungus and helps in nutrient absorption. For example, Monotropa.
3. Clinging roots are many short branch like adventitious roots arise from nodes. For example, Piper betel.
4. Adventitious roots are the roots that develop from any part of plant other than radicle. For example, banyan tree

In some plants, root get modified for storage and are of mainly four types:-

The taproot is the primary root which develops from the elongation of the radicle of the embryo and persists throughout the life of the plant. It forms lateral or secondary roots which further divided to form tertiary roots.

Functions of root:-

Utricularia is an insectivorous plant. It does not have roots because it is specially modified to trap insects for feeding, so its vegetative organs are not seperated into roots stems and leaves.

$\to$ Endodermis is followed by one or more layers of pericycle.

• The parts which arise from the cortical region or the cortex are called exogenous in origin.
• The parts which arise from the pericycle are called endogenous origin.
• The lateral roots or root branches originate endogenously as they originate from the pericycle.
  
• So, the correct answer is 'Root branches are endogenous'

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

• The root-promeristems that contain the initials of epidermis, cortex and stele is known as Quiescent centre.
• 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 'Quiescent centre'

A plant with epidermis specialized to absorb moisture from the air is Vanda because vanda is an epiphyte with modified epidermis called velamen. As it stays on the host plant branches, its roots hang in the air absorbing moisture from the atmosphere.

Lateral roots arise endogenously from other roots and increase the absorptive surface of the plant. Most lateral roots are initiated some distance basipetal to the apical meristem, differentiated cells must become reprogrammed to give rise to the initial divide and enlarge in very precise patterns to organize a new organ recognizable as a root. 

• The quiescent centre is that part of the root-promeristems that contains the initials of epidermis, cortex and stele which divides less frequently and are present at the pole of cortex and stele.
  
• In closed meristems, QC is hemispherical in shape whereas, in open meristem it is disc-shaped. 
• The cells with QC have small dictyosomes, nuclei and nucleoli. 
• 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 'All of the above'.

The small, tubular, unicellular outgrowths formed from the root epidermal cells called root hairs.

So, the correct option is ‘Always unicellular’.

When the tunica is multilayered, the condition is called multistratose tunica. The layers of tunica can be designated as L1, L2, L3 and so forth. The L1 or the outermost layer of the tunica would give rise to the epidermis and the rest of the layers would form the cortex and the vascular tissues, as seen in Datura.

• The quiescent centre or QC is a part of the root-promeristems that contains the initials of epidermis, cortex and stele.
  
• The cells here 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 'Light cytoplasm and small nuclei'.

Rootlets are also called as lateral root and are defined as the small branches of roots that form from the main root and helps the plant for the absorption of water and minerals as they increase surface area.

In dicot roots, the xylem arrangement is exarch, meaning the protoxylem is located towards the periphery and the metaxylem is towards the center.

Salvinia is an aquatic fern where the modified leaves act as root-like structures to absorb water and nutrients.

The protoplasm of the cell is surrounded by a primary cell wall which is laid down as the cell begins to grow. It is thin and composed of cellulose, hemicellulose and pectic substances. Once growth has ceased a secondary cell wall may form inside the primary cell wall.

Dicot root shows radial vascular bundles, i.e., vascular bundles arranged in a ring. In this type of vascular bundle, the xylem and phloem are situated at different radii. Xylem is of exarch type, i.e., protoxylem is away from centre and metaxylem is towards centre. Hence, statement (a) is wrong.
The innermost layer of cortex in a dicot root is endodermis. It completely surrounds the stele. It consists of single layer of barrel shaped cells which lack intercellular spaces. Hence, statement (b) is correct. 
In a dicot root, the phloem masses are separated from the xylem by conjunctive tissues. Later, vascular cambium forms from this conjunctive tissue. Hence, statement (c) is correct. 
Thus, the correct answer is '(a) is false; but (b) and (c) are true'.

In the root cap there is a special subset of cells, called as statocytes. Inside the statocyst cells, some specialized amyloplasts are involved in the perception of gravity by the plant (gravitropism). Statoliths settle at the bottom part of their cells and allow plants to sense gravity. Statoliths are also found in the endodermal layer of the inflorescence stem. The redistribution of auxin causes the shoot to turn in a direction opposite that of the gravity stimuli.

The cortex is the outermost layer of the stem or root of a plant, bounded on the outside by the epidermis and on the inside by the endodermis. In plants, it is composed mostly of differentiated cells, usually large thin-walled parenchyma cells of the ground tissue system.

Roots produced other than radicle are called adventitious roots. These are formed from pericycle or interfascicular cambium.

So, the correct option is ’Pericycle or interfascicular cambium’.

The region of cell differentiation or maturation is differentiated into root hairs. Most of the water absorption occurs through this region.

Quiescent centre is present in the apical meristem of the root also called the root apex. It occur in the form of a hemisphere. 

Outer most part of the stele is pericycle . It is found in roots and dicot stem. in roots it is parenchymatous. In dicot root it is involved in the formation of lateral roots and in monocot roots it is involved in the formation of lateral roots.

• The epidermal cells of the roots give out fine hair-like outgrowths called the root hairs that absorb water and minerals

Pisum sativum, also called pea plant has nodulated roots because they are found in association with a nitrogen-fixing bacterium called Rhizobium. This rhizobium resides in these nodules.

• Vegetative parts of the plant include roots, stem, leaves 

The ability to bend and growing the root towards a moisture gradient is essential because plants need water to grow. Water, together with soluble mineral nutrients, is taken up by the root hairs. Then, in vascular plants, water and minerals are transported to all parts of a plant through a lignified transport system called as xylem. The second transport system in vascular plants is called as phloem. The phloem also carries water, not with soluble minerals, but mainly with soluble organic nutrients instead. These organic nutrients are delivered by photosynthesis and are called as photosynthate. 

A. Adventitious roots are the roots which are produced from other plant parts like stems, leaves etc.

Root cap takes part in the protection of root meristem because it is the layer separating the meristem from the external forces. It protects the tender apex while root makes its way into the soil.