RBSE Solutions for Class 11 Biology Chapter 17 Root: External Morphology

RBSE Solutions for Class 11 Biology Chapter 17 Root: External Morphology

Rajasthan Board RBSE Class 11 Biology Chapter 17 Root: External Morphology

RBSE Class 11 Biology Chapter 17 Multiple Choice Objective Questions

Question 1.
From which part of plant, root arises?
(a) Plumule
(b) Radicle
(c) Seed coat
(d) Seed embryo

Question 2.
The root arises from other then radicle is called which root
(a) Tap root
(b) Fibrous root
(c) Lateral root
(d) Adventitious root

Question 3.
Root hairs are found in which zone of root apex
(a) Static zone
(b) Meristematic zone
(c) Maturation zone
(d) Elongation zone

Question 4.
The shape of root of carrot is
(a) Conical
(b) Tuberous
(c) Napiform
(d) Fusiform

Question 5.
Lateral roots originate from
(a) Pericycle
(b) Epidermis
(c) Peribleme
(d) Xylem bundles

Question 6.
Out of the following which plant part cannot be considered as root
(a) Radish
(b) Colocassia
(c) Sweet potato
(d) Dahelia

Question 7.
In banyan tree, following is found
(a) Prop roots
(b) Stilt roots
(c) Mycorrhiza root
(d) Parasitic root

Question 8.
In maize, roots are developed from-
(a) from nodes of stem
(b) from leaves
(c) Inflorescence
(d) shoot apex

Question 9.
Hygroscopic roots are found in
(a) Mangroove trees
(b) Epiphytic roots
(c) Aquatic roots
(d) Xerophytes

Question 10.
Parasitic roots are found in
(a) Maize
(b) Potato
(c) mistletoe
(d) Teak

Answers:
1. b, 2. d, 3. c, 4. a, 5. a, 6. b, 7. a, 8. a, 9. b, 10. c

RBSE Class 11 Biology Chapter 17 Very Short Answer Questions

Question 1.
Respiratory roots are found in which plants?
Answer:
Plants in marshy areas e.g. Mangrove plants.

Question 2.
Hygroscopic root are found in epiphytic roots?
Answer:
Epiphytic or Aerial absorbing roots absorb atmospheric moisture by hygroscopic roots.

Question 3.
What are the function of Root cap/calyptra?
Answer:
Function of Root Cap / Calyptra:

1. Protects root meristem,
2. Secrete mucilage that help tender root to penetrate the hard soil
3. Helps in perception of gravity (Darwin, 1880)
4. Root packet’s functions as balances.

RBSE Class 11 Biology Chapter 17 Short Answer Questions

Questions 1.
How many types of root are there? Write the names of them.
Answer:
Types of Roots: On the basis of their origin, roots are of two types – tap root and adventitious root.
(a) Tap root:
On germination of a seed, the radicle elongates into primary root or true root or tap root. In dicot plants, the tap root is persistent and produces lateral roots such as secondary roots, tertiary roots etc. All lateral roots arise in acropetal succession i.e. younger roots towards apex and older roots towards base. The tap root and its branches constitute the tap root system.

(b) Adventitious root:
These are the roots that grow from any part of the plant other than radicle. In monocot plants, the tap root is short lived and soon replaced by adventitious roots. A group of adventitious roots and their branches constitute adventitious root system. On the basis of their origin, the adventitious roots are of following three types –

• Fibrous roots:
  These are a cluster of equally prominent thread-like roots that develop either from the base of stem (e.g., rice, wheat, maize, onion etc.) or from the nodes of horizontal stem (e.g., grass, wood sorrel etc.)
• Foliar roots:
  They arise from petiole (e.g., Pogostemon, rubber plant etc.) or veins of leaf due to some injury. These can also be induced by application of hormones. Some foliar buds can produce foliar roots, e.g.,Bryophyllum, Begonia etc.
• True adventitious roots:
  They arise from the nodes and intemodes of the stem, e.g.,Prop roots of banyan, stilt roots of sugarcane, clasping roots of money plant and roots from the stem cuttings.
  

Questions 2.
What are the function of root?
Answer:
Functions of Roots:
Roots perform two kinds of functions Primary and Secondare. The primary functions are performed by all kinds of roots, and they are structurally adapted to per-form these functions. The secondary functions are specialized one and are performed only by those roots which are modified accordingly.
(A) The primary functions of roots are:

1. Anchorage: The roots anchor or fix the plant to the substratum or soil and provide mechanical support to the aerial part of the plant.
2. Absorption: Roots perform very important function of absorption of water and minerals from the soil in almost all the terrestrial plants. Since these functions are not critical in submerged aquatics, the roots are poorly developed or totally absent in them (e.g. Ceratophyllum, Utriculciria, etc.)
3. Conduction of water and minerals: Upward movement of absorbed water and minerals is done by roots. Root pressure also plays an important role in this process.
4. Translocation of organic nutrients. Roots are non – green: They lack chlorophyll and they are incapable of photosynthesis. Sugar, produced in the leaves by photosynthesis, is transported downward to the tissues of the root where it is metabolised.

(B) The Secondary Functions of root are:

1.  Food storage. It occurs mainly by fleshy roots. Examples – Carrot, Radish, Beet, Sweet potato, Turnip, Asparagus, Dahlia, Curcuma, etc.
2. Additional mechanical support: In some plants, roots are modified to provide additional mechanical support. Examples – prop roots (e.g., Banyan, Rhizophora), stilt roots (e.g., Maize, Sugar-cane, Pandanus. etc.), buttress roots (e.g., Bomb ax), etc.
3. Haustorial roots: Roots of some parasitic plants act as haustoria e.g., Cuscuta). They penetrate upto phloem of host and absorb nourishment.
4. Assimilation: Roots of some plants are photosvnthetic. e.g., Trapa, Taeniophyllum, Tinospora, Podostemum.
5. Aeration: Roots of some plants help in exchange of gases, e.g., Rhizophora, Sonneratia, Heritiera.
6. Symbiotic nitrogen fixation: Roots of leguminous plants have nodules containing nitrogen fixing bacteria.
7. Floating and balancing: Roots of some aquatic plants store air and help in floating and balancing, e.g.,Jussiaea (= Ludwigia), Pistia, Eich – homia, etc.
8. Hygroscopic roots: Aerial roots absorb moisture from the air e.g., epiphytic plants, Orchids, young prop roots of Banyan, etc.
9. Reproduction: Some modified roots possess adventitious buds which grow to produce new plants and help in vegetative propagation, e.g.. Sweet potato, Dalbergia, etc.
10. Climbing: Some weak stemmed plants develop climbing roots which help the plant to climb up the support, e.g.,Betal, Money plant, Tecomct, etc.

Question 3.
Differentiate between Tap root and adventitious roots?
Answer:

S.No	Tape Root System	S.No	Adentitious Root System
1.	The radicle of embryo gives rise to branches of primary, secondary or higher orders form the tap root system.	1.	The root system developing from any-where excepting the radicle is known as adventitious root system.
2.	The primary root, formed from the elongation of radicle, is long lived.	2.	The primary root is short-lived.
3.	It has a prominent primary root on which the lateral branches arise in acropetal succession (i.e.,youngest at the tip and oldest at the base).	3.	Primary root is soon replaced by adventitious roots so that all the roots are of uniform thickness forming cluster.
4.	Tap root system may be deep feeder (as in tall trees) as well as surface feeder (as in herbs).	4.	Adventitious root system is usually surface feeder.
5.	This system is usually found in dicots.	5.	This system is usually found in monocots as well as in those plants which require root modifications for specialised functions.

RBSE Class 11 Biology Chapter 17 Essay Type Questions

Question 1.
Write in detail how the roots are modified as mechanical tissue with help of well labelled diagram?
Answer:
modified as mechanical tissue:
1. Prop Roots:
In some tropical trees like Ficus bengahtensis (banyan), the horizontal aerial branches give rise to aerial roots which are provided with root-caps and hang vertically down from the boughs like so many strings. These grow down and, on reaching the soil and becoming anchored, they begin to stouten and ultimate become almost as strong as the main trunk. They support or prop up the horizontal branches like so many pillars.

Ultimately, the main trunk may die when the prop roots fully replace it. Long living banyan trees cover large areas by their spreading branches supported on prop roots. The banyan tree at the Indian Botanical Garden, Shibpur, Calcutta is about 200 years old, covers a large area and has produced more than 900 prop roots. A similar tree in the Theosophical Society compound Adyar, Madras and another in the Buitenzorg Botanical Garden, Java, are equally remarkable.

2. Stilt Roots:
Certain shrubs and small trees like screw-pine (Pandanus foetidus) grow on the edges of tanks, marshes, etc., where the anchorage is not very strong. In these cases, short roots grow obliquely downwards from near the base of the stem and act like stilts providing additional support as well as anchorage to the stem. The adventitious roots growing from the lower nodes of maize plants act in a similar way. Such stilt roots are also seen in mangrove plants like Rhizophora.

3. Root Buttresses:
In some large trees, instead of stilt roots, there are great plank-like roots radiating from the base of the tree like wings These are called buttresses and are actually partly root and partly stem They may be seen in old trees of Bombax ceiba, Terminalia catappa, Ficus sp., etc.

4. Climbing Roots:
Some climbers can climb up their supports as adventitious roots growing from the nodes of the frail climber twine round and clasp the support as if the climber has been tied to the support at those points. Common examples are to be found in the aroid Scindapsus officinalis, the betel vine etc.

5. Clinging Roots:
Epiphvtes like orchids cling to their support by means of special clinging roots which enter the crevices of the support and fix the epiphvtc Clinging roots may carry on some absorption but are different from the specialised aerial absorbing roots.

6. Haptera or Holdfasts:
The thalloid branching root of Podostemaceae , which is their main plant body carrying on assimilation as well as reproduction, is stuck up to the rock by means of special root processes which may be called holdfasts or haptera as in some algae. The adhesive discs of adhesive climbers like Ficus repens and Ivy are also types of hold fasts. It may be noted that all the three types of roots, climbing, clinging and hold-fasts, may behave in the same way by becoming flattened and disc – like and sticking to their supports or to the substratum.

7. Contractile or Pull Roots:
In plants with underground stems (rhizome, bulb, tuber, corm), there are certain roots which are different from the others as they are found to contract or swell so that the aerial shoot or the underground parts arc kept at a proper level in the soil. These roots are, therefore, called pull or contractile roots. Those may be seen in Canna, Crocus, Allium, Lilium, etc.

8. Floating Roots:
Certain aquatic floating plants like fussiaea repens (Onagraceae) have special roots growing from the nodes in addition to the ordinary adventitious roots. These roots look like masses of white cotton and are extremely spongy in nature. Their buoyancy helps to keep the plant floating. If taken out of water they dry and shrivel up quickly. The large amount of air contained in the floating roots may also be of some use in the aeration (‘breathing’) of the submerged organs.


9. Root – Thorns:
In many palms (e.g., Acanthorhiza and Iriartea), some aroids (Pothos armatus) and others, adventitious roots from the base of the stem become hard pointed and thron – like. These are called root – thorns. A They are of indirect help as an Armature to the plants in driving out marauding animals. Old adventitious roots of coconut, etc., also serve the same purpose.

Question 2.
How tap root and adventitious roots are modified for storage function with help of well labelled diagram?
Answer:
Modification for Storage of Food – Stoage Roots:
In some plants, the primary’ tap roots are modified for storing reserve food materials. The secondary roots remain thin and they are absorptive in function. The storage roots are usually swollen and assume various Roots are modified into different forms to perform specific functions other than their normal functions. Modification in

• Conical: The swollen root is broad at the base and tapers gradually towards the apex giving a shape of cone, e.g., Carrot.
•  Fusiform: The root is swollen in the middle and narrow towards both its base and apex giving a shape of spindle, e.g., Radish. Half or less than half portion towards the base of fusiform root is formed by hypocotyl.
• Napiform: The root is nearly globular or spherical in shape. The basal portion of root is much swollen which suddenly tapers towards the apex giving a top – shaped appearance, e.g., Turnip (Brassica napus, vern. Shazgam) and Beet (Beta vulgaris, vern. Chukandar).
• Tuberous: The storage root having no definite shape is called tuberous, e.g., Mirabilis jalapa (4 O’clock plant), Trichosanthes (vem. Par-wal), Echinocystis Zobata (The tuberous root is lobed and weighs as much as 22 kg.).
  

Modifications of Adventitious Root:
1. Roots modified for storage of food:

• Tuberous roots: Some of the adventitious roots store food materials and become swollen. They arise singly and do not attain a definite shape, e.g., Sweet potato (Ipomoea batata). The tubers of sweet potato also bear adventitious buds and behave as reproductive roots. They arise from the nodes of running stem.
•  Fasciculated roots: The swollen tuberous roots, when occur in clusters, are called fasciculated roots. Examples are – Dahlia, asparagus, etc. In Dahlia, cluster of tuberous roots he at the base of stem. In asparagus, the fleshy roots occur at intervals on the normal roots.
• Palmate tuberous roots: Some fleshy roots are palmate in shape, called palmate tuberous roots. In some orchids, they appear as palm of human hand.
•  Nodulose roots: The adven – titious roots swell only near their apices like single beads, e.g., Mango, ginger (Curcuma amada), Cosuts speciosus, etc.
• Moniliform roots:  These roots are alternately swollen and constricted giving a beaded appearance, e.g., Dioscorea alata, Basella rubra (Indian spinach vem. Kulfa), Momordica charantia (Bitter gourd), etc.
• Annulated roots:  These thickened roots look as if formed by a number of discs placed one above another, e.g., Ipecac (Psychotria ipecacuanha).
  

Question 3.
Explain the different zones of root apex with help of well labelled diagram?
Answer:
A typical root can be differentiated into five regions. From apex to base they are:

(a) Root Cap (Calyptra):

1. It is a cap like protective structure of the growing root tip.
2. In Pandanus (screwpine) multiple root caps present while in aquatic plants (Pistia, Eichhomia, Lemna) root pockets present instead of root cap.
   Function: 
   • Protects root meristem,
   • Secrete mucilage that help tender root to penetrate the hard soil,
   • Helps in perception of gravity,
   • Root packets functions as balances.

(b)  Growing point or Meristematic Zone:

1. It is about 0.25 – 1.0 mm long, lies just behind the root cap and thus sub-terminal in position.
2. Its shape is like an inverted concave dome of cells.
3. The central rarely dividing cells are called quiescent centre.
   Function: 
   • Root meristem adds cells to root cap and the basal region of the root.

(c) Zone of elongation:

1. It is about 1 -10 mm long and lies just behind the meristematic zone.
2. As the name implies, it is the site of rapid and extensive cell elongation.
3. This zone increases length of the root.
4. The external cells can absorb water and minerals from the soil.

(d) Root hair Zone or Zone of differentiation:

1. It is about 1 – 6 cm long.
2. It is the zone where cell differentiate to form epiblema, cortex, endodermis, pericycle, xylem and phloem.
3. Many cells of epiblema elongate to form unicellular root hairs.
4. As the root grows, new root hairs develop and older one shrivel and sloughed off.
   Function: 
   • Root hairs increase the absorptive surface area of root.

(e) Zone of maturation:

1. It constitute the major portion of the root.
2. The cells attain maturity when they reach this zone. Function
   • Lateral roots may emerge from pericycle.
   • Radial differentiation of tissues causes secondary growth in dicots.

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