RBSE Solutions for Class 11 Biology Chapter 15 Internal Structure of Root, Stem and Leaf

RBSE Solutions for Class 11 Biology Chapter 15 Internal Structure of Root, Stem and Leaf

Rajasthan Board RBSE Class 11 Biology Chapter 15 Internal Structure of Root, Stem and Leaf

RBSE Class 11 Biology Chapter 15 Multiple Choice Objective Questions

Question 1.
Casparian strips are found in:
(a) Cuticle
(b) General cortex
(c) Endodermis
(d) Pith

Question 2.
In T.S. of dicot stem we observe:
(a) Scattered Vascular bundle
(b) Vascular bundle present in ring
(c) radial vascular bundle
(d) losed vascular bundle

Question 3.
In T.S. of monocot stem, we observe:
(a) scattered
(b) arranged in ring
(c) open vascular bundle
(d) radial vascular bundle

Question 4.
Vascular bundle in root are:
(a) Conjoint
(b) Collatoral
(c) Open
(d) Radial

Question 5.
Mesophyll is
(a) Chlorenchymatous
(b) Sclerenchymatous
(c) Meristematic
(d) made from bulliform cells

Answers:
1. c, 2. b, 3. a, 4. d, 5. a

RBSE Class 11 Biology Chapter 15 Very Short Answer Questions

Question 1.
Which type of vascular bundles are found in root?
Answer:
Radial.

Question 2.
What are conjunctive tissue?
Answer:
In between the xylem and phloem patches of paren – chymatous cells are found in root. This tissue is called conjunctive tissue.

Question 3.
What is hairy layer?
Answer:
Presence of hairs on epidermis.

Question 4.
How many type of Stele are formed on basis of number of xylem?
Answer:
1.Protostele = solid core of xylem, has no pith, no leaf gaps
2. Siphonostele = hollow cylinder of xylem, has pith, has leaf gaps
3. Eustele = xylem and phloem located in vascular bundles, sympodia, has pith, does not have leaf gaps.

Question 5.
How are vascular bundles are arranged in monocot stem.
Answer:
The vascular bundles are numerous and scattered in parenchymatous ground tissue (except in runners and grasses). They are smaller in size towards periphery aftd larger towards centre. Each vascular bundle is conjoint, collateral, endarch and closed.

Question 6.
How the vascular bundles are arranged in Dicot stem?
Answer:
The vascular system of dicotyledonous stem consists of a large number of vascular bundles arranged in ring between cortex and pith. Each vascular bundle is conjoint i.e., xylem and phloem both are present in the same radius. They are usually collateral, i.e., the phloem lies towards the outerside of xylem (e.g., Helianthus) or bicollateral, i.e., the phloem is present on either side of xylem (e.g., Cucurbita). In some cases, the vascular bundles are concentric type as in case of Begonia, Rumex, etc., they are amphivasal type, i.e. the phloem lies in the centre surrounded by xylem. The vascular bundles are open, i.e., cambium is present between the xylem and phloem.

Question 7.
Where the bast or hard bast is found?
Answer:
The thick – walled patches usually occur above the primary phloem and have been called hard bast. The thin-walled patches usually occur above the primary medullary rays. The thick – walled sclerenchymatous fibres are also called primary extraxylary fibres found in Dicot Stem.

Question 8.
What are ground tissue?
Answer:
Ground tissue: In case of monocot stem, the cortex, endodermis, pericycle and pith are absent. The entire mass from hypodermis to the centre is called ground tissue. The ground tissue is made up of parenchymatous cells.

Question 9.
What are lysogenous cavity?
Answer:
This type of intercellular space arises through dissolution of entire cells, which are therefore called lysigenous intercellular spaces (lysis, loosening, Greek). These cavities of intercellular spaces store up water, gases and essential oils in them. The examples are commonly found in water plants and many monocotyledonous plants. The secretory cavities in Eucalyptus, Citrus and Gossypium are good examples.

Question 10.
Dorsiventral leaves are devoid or very less number of stomata. What are the benefits of this to plant.
Answer:
Less or no stomata on upper epidermis prevent water loss on exposure to sunlight.

RBSE Class 11 Biology Chapter 15  Short Answer Questions

Question 1.
What are the anatomical features of structure of root?
Answer:

1. Outermost layer is named as epiblema  (= piliferous layef = rhizodermis) which bears large number of short lived unicellular hair, Cuticle and stomata are absent.
2. Cortex is made up of parenchymatous cells.
3. Endodermis is very distinct.
4. Pericycle is very distinct.
5. Vascular bundles are radially arranged.
6. Xylem is exarch i. e., protoxylem is towards the periphery and metaxylem towards centre.
7. Phloem is made up of sieve tubes, companion cells and phloem parenchyma. (Phloem parenchyma is absent in monocotyledonous plants).
8. In between the patches of xylem and phloem is found parenchyma which is called conjuctive tissue.
   • For studying similarities and differences of internal structure of monocot and dicot root, we will study with help of transverse section of maize and gram respectively.

Question 2.
How you will differentiate between monocot and dicot root?
Answer:

Character	Dicot root	Monocot root
1. Pericycle	Gives rise to secondary roots and lateral meristem	Gives rise to lateral roots only
2. Vascular bundles	Diarch to hexarch	Hexarch to polyarch
3. Cambium	Develops at the time of secondary growth	Absent
4. Pith	Absent or poorly developed	Fully developed.

Question 3.
Draw a well labelled diagram of T.S. of monocot root?
Answer:
Internal Structure of Orchid Root: Most orchids are epiphytes. They have hanging aerial roots. Their anatomy is different from other monocotyledonous roots and is as follows:
1. Velamen:

• It is the outermost tissue of the root.
• The cells of this tissue are large, closely packed, with fibrous thickenings.
• These are dead cells. These cells are filled with air in dry season and during rains these cells absorb water.
• Velamen is like a multilayered epiblema.
• The outermost layer of velamen is called limiting layer. It is cuticularized.

2. Exodermis:

• It is the outermost layer of the cortex.
• The lateral walls of the exodermal cells are thickened.
• Passage cells are found here and there.

3. Cortex:

• The cortex is made up of thin walled parenchymatous cells.
• The innermost layer of the cortex is endodermis.
• All tissues enclosed by the endodermis are called stele.

4. Pericycle:

• It is one layered tissue on the inner side of endodermis.

5. Conjunctive tissue:

• It is the parenchymatous tissue surrounding and in between the vascular bundles.

6. Vascular bundles:

• Vascular bundle are radial. Xylem and phloem are present as alternate patches and are situated in a ring.
• Vascular bundles are more than six. Xylem is exarch.
  

Question 4.
Draw a well labelled diagram of T.S. of dicot stem?
Answer:

Transverse section of young stem of Sunflower (Helianthus annuus)

Detailed structure of a portion of T.S. of sunflower stem.

Question 5.
Write salient features of Monocot leaf?
Answer:
Most of the monocotyledonous leaves are isobilateral but in some plants (Canna, Lilium, Musa, etc.), they are dorsiventral. The leaves usually show parallel venation. Each leaf is differentiated into leaf blade (lamina) and leaf sheath. In some cases, they may be petiolate. The monocotyledonous leaves also possess three distinct tissue systems –

1. epidermis (epidermal tissue system),
2. mesophyll (the ground tissue system) and
3. vascular system

1. Epidermis:

1. Each leaf has upper and lower epidermis made up of single layer of compactly arranged cells.
2. The outer cells of epidermal cells are coated with thick or thin cuticle.
3. In many grasses, the epidermal cells are impregnated with silica. The stomata are generally found on both the upper and lower epidermis.
4. In some free floating hydrophytes and a few grasses, the stomata are found only on upper epidermis.
5. All the epidermal cells are alike but in Poa pratensis, Ammophilla arenaria, Zea mays and many grasses, the epidermis is made up of two types of cells.
   • Either upper or lower epidermis bears groups of large
   • bubble-like cells in addition to ordinary epidermal cells. ‘
   • These bigger cells are called bulliform cells or motor cells.
   • These cells may be distributed irregularly or arranged in regular pattern.
     These cells, by osmotic changes, help in the rolling and unrolling of leaves to regulate loss of water.

2. Mesophyll:

1. The bulk of tissues lying between upper epidermis and lower epidermis (except vascular bundles) is called mesophyll.
2. The mesophyll is either composed of similar types of cells (e.g., maize) or differentiated into palisade and spongy

parenchyma.

1. The monocot leaves are generally isobilateral and, therefore, the palisade is present on both upper and lower sides and the spongy parenchyma occupies the central position.
2. All the cells of mesophyll contain chloroplasts and perform photosynthesis.
3. These cells are separated by intercellular spaces which are interconnected and open into sub-stomatal chambers to maintain continuity with external atmosphere through stomata.
4. A few monocot leaves are dorsiventral and possess palisade only below the upper epidermis (e.g., Lilium; Canna, Musa, etc.).

3. Vascular system:

1. The monocot leaves are characterized by possessing parallel venation.
2. Each vein comprises of single vascular bundle.
3. Each bundle is conjoint, collateral and surrounded by distinct bundle sheath. ,
4. In some cases, the bundle sheath is connected with upper and lower epidermis by groups of compact parenchymatous or sclerenchymatous cells called the bundle sheath extensions.
5. The extensions are more pronounced in the mid-rib region.
6. Each vascular bundle consists of xylem facing towards upper epidermis and phloem towards lower epidermis.
7. In some cases, the phloem lies towards upper side and xylem towards lower side. The xylem and phloem elements are similar to those of dicotyledonous leaves.

Question 6.
What is mesophyll tissue and how it is differentiated in leaf of Dicot plants?
Answer:
Mesophyll:
The bulk of tissue lying between upper and lower epidermis (except vascular bundles) is called mesophyll. It consists of parenchymatous cells containing abundant chloroplasts and separated by lots of intercellular spaces. In some leaves (e.g., Hydrophytes), it is made up of one type of cells but In others the mesophyll is differentiated into palisade parenchyma and spongy parenchyma.

The palisade is made up of compactly arranged columnar cells elongated at right angles to the leaf epidermis. The spongy parenchyma, on the other hand, consists of loosely arranged cells (spherical,oval, and are irregularly arranged) with wide intercellular spaces. These spaces are interconnected and open into substomatal chambers to maintain gaseous exchange through stomata.

Besides palisade and spongy parenchyma, the mesophyll also possess different kinds of sclereids. For example, the leaves of Hakea possess osterosclereids (rod-shaped stone cells) among palisade. Some hydrophytes possess branched sclereids in their larger air spaces (Nymphaea) or sphaeraphides in specialized cells (e.g., Trapa bispinosa).

Question 7.
Why the ventral surface is lighter green in Dorsiventral leaves?
Answer:
Less exposed to sunlight.

Question 8.
What is Bundle sheath and what is difference of it in dicot and monocot?
Answer:
In Dicot leaf made up of parenchyma above and below the vascular bundle some parenchymatous cells or collenchymatous cells are present up to epidermis but in monocot root it is just made of parenchyma but just above and below the vascular bundles are fount sclerenchymatous cells(upto epidermis).

Question 9.
Differentiate between T.S. of Monocot and dicot stem?
Answer:

RBSE Class 11 Biology Chapter 15 Essay Type Questions

Question 1.
Explain the internal structure of Dicot root with help of well labelled diagram and also differentiate between vascular bundle od Monocot and dicot root?
Answer:
1. Epiblema:

• ( = piliferous layer = rhizodermis)
•  It is the outermost layer.
• Consists of thin walled, living parenchymatous cells.
• The outer walls of the cells of epiblema form unicellular tubular prolongations called root hairs.
• These hairs help in absorption of water from the soil.

2. Cortex:

• It is situated below the epiblema upto endodermis.
• It is made up of thin walled circular or polygonal living parenchymatous cells with numerous intercellular spaces.
• Cortical cells store starch.

3. Endodermis:

• The innermost layer of cortex that surrounds the stele is called endodermis.
• Cells of endodermis have special thickenings called casparian strips in their radial and tangential walls.
• Endodermal cells outside the protoxylem, do not have casparian strips.
• Such cells are called passage cells.

4. Pericycle :

• This unilayered structure is found inside the endodermis.
• Consists of thin waded cells.

5. Vascular bundles:

• These are always arranged in a ring and are radial i. e., Xylem and phloem are situated at different radii.
• The protoxylem is always away from the centre and metaxylem towards the centre.
• This condition of xylem is called exarch.
• The vascular bundles in gram root are tetraeh.

6. Conjuctive tissue:

• In between the xylem and phloem patches of paren-chymatous cells are found called as conjunctive tissue.

7. Pith:

• It is found in the centre and is feebly developed.
• It is made up of parenchymatous cells with intercellular spaces.
  
  
  T.S. of Dicot Root (Gram) (A sector enlarged)

Orchid Root:
Vascular bundles:

• Vascular bundle are radial. Xylem and phloem are present as alternate patches and are situated in a ring.
• Vascular bundles are more than six. Xylem is exarch.

Dicot Root:
Vascular bundles:

• These are always arranged in a ring and are radial i. e., Xylem and phloem are situated at different radii.
• The protoxylem is always away from the centre and metaxylem towards the centre.
• This condition of xylem is called exarch.
• The vascular bundles in gram root are tetraeh.

Question 2.
Explain the T.S. of monocot stem with help of well labelled diagram and also differentiate between cortex of Dicot and monocot stem?
Answer:
Internal Structure of Mon ocot Stern:
A typical monocotyledonous stem shows the following internal structures from periphery to centre (Typical example: Zea mciys)

1. Epidermis:
The epidermis is outermost single layered protective covering made up of living parenchymatous cells. The outer walls of epidennal cells arc highly cutinised. A few stomata may be present. Multicellular hairs are usually absent.

2. Hypodermis:
The epidermis is followed by a few layers (2-4 layers) of sclerenchinatous hpoderrnis. The cells possess lignified cell walls and it provides,
mechanical strength to the stein. Intercellular spaces are absent. In some cases, the hvpodermis may be absent (Wheat, Asparagus etc.).

3. Ground tissue:
In case of monocot stem. the cortex, endodermis, pericycle and pith are absent. The entire mass from hvpodcrmis to the centre is called ground tissue. The ground tissue is made up of parenchymatous cells. The cells of ground tissue towards outerside are smaller polygonal and compact whereas those towards centre.The cells of ground tissue towards outerside are smaller polygonal and compact whereas those towards centre are Large. oval rounded and loosely arranged. These cells contain starch grains.

4. Vascular system:
The vascular bundles arc numerous and scattered in parenchvmatous ground tissue (except in runners and grasses).They are smaller in size towards periphery and larger towards centre. Each vascular bundle is conjoint, collateral, endarch and closed. Each vascular bundle is parenchymatous surrounded by a sheath of scierenchymatous fibres.

(a) Xylem: The Xylem consists of vcssels,tracheids and xylem parenchvma.The xylem is Y- shaped or V-shaped with two big oval metaxylem vessels occupying the divergent ends of Y’ and no smaller protoxvlcm vessels occupying the lower arm of the Y. Metaxvlcm faces towards periphery and protoxylem towards centre. There is a water-containing lvsigenous cavity at the end of protoxylem vessels fonned by dissolution of inner protoxvlem vessel and parcnchv ma.

(b) Phloem: The phloem lies toards outerside. It consists of sieve-tubes and companion cells only. The phloem parenchyma are absent. Phloem can be distinguished into an outer crushed protophloem and inner metaphloern and metaphlocm is functional.

Diagrammatic representation of T.S. of young maize stem.
Detailed structure of a portion of T.S. of maize stem.

Detailed structure of one vascular bundle of maize

Internal Structure of Dicot Stem: A typical dicotyledonous stem (T.S. of stem of sunflower) shows the following internal structure from periphery to centre.

1. Epidermis:
The epidermis is outermost single layered protective covering made up of compactly arranged parenchvmatous cells. The cells are rectangular in transverse section. The outer walls of cells are highly cutinised or coated with wax. The stomata may be present in young stem.The epidermal outgrowths include prickels, spines or glandular or non-glandular hairs. The hairs are usually multicellular.

2. Cortex:
The epidermis is followed by a few to several layered thick distinct zone, called the cortex. It may be entirely made up of parenchymatous cells (e.g; Ranunculus, Fumaria) or differentiated into two parts – hypodermis and cortex. The hypodermis of young stem is collenchymatous (3-5 layers). The intercellular spaces are absent and the comers of the cells are thickened due to deposition of extra cellulose impregnated with pectic substances . These cells have chloroplasts. Rest of the cortex is made up of loosely arranged parenchymatous cells, which are spherical or oval with some intercellular spaces.

3. Endodermis :
The endodermis is the innermost layer of cortex. In most of dicotyledonous stem the endodermis is not distinct. It consists of single layer of barrel shaped cells which may contain starch grains and lack casparian strips.Due to presence of starch grains in these cells, this lqyer is also called starch sheath.

4. Pericycle :
The pericycle of dicotyledonous stem is a layer or layers found between the endodermis and vascular cylinder. It is made up of alternate bands of parenchymatous and sclerenchymatous cells. It may be in the form of continuous cylinder of sclerenchymatous tissue (e.g., Cucurbita) or in the form of alternating patches of thick-walled and thinwalled cells (e.g., Helianthus). The thick-walled patches usually occur above the primary phloem and have been called hard bast, The thin-walled patches usually occur above the primary medullary rays. The thick-walled sclerenchymatous fibres are also called primary extraxylary fibres.

5. Vascular system:
The vascular system of dicotyledonous stem consists of a large number of vascular bundles arranged in ring between cortex and pith. Each vascular bundle is conj oint, i. e., xylem and phloem both are present in the same radius. They are usually collateral, i. e., the phloem lies towards the outerside of xylem (e.g, Helianthus) or bicollateral, i.e., the phloem is present on either side of xylem (e.g., Cucurbita). In some cases, the vascular bundles are concentric type as in case of Begonia, Rumex, etc.,

they are amphivasal type, i. e. the phloem lies in the centre surrounded by xylem.The vascular bundles are open, i. e., cambium is present between the xylem and phloem. The phloem consists of sieve tubes, companion cells, phloem parenchyma and phloem fibres. The xylem consists of vessels, tracheids, xylem fibres and xylem parenchyma. The xylem is endarch, i.e., the protoxylem lies towards pith and metaxylem towards periphery.

6. Medullary rays:
The primary medullary rays are parenchymatous areas between the two adjacent vascular bundles.
Provide pathways of radial conduction of food and water.7. Pith:
The central portion of dicotyledonous stem is occupied by large, thin-walled parenchymatous cells with intercellular spaces. Sometimes it is represented by hollow cavity.

Transvrse section of young stem of sunflower

Question 3.
Explain the internal structure of dorsiventral leaf with help of well labelled diagram? Differentiate between internal structure of Dorsiventral and Isobilateral leaf?
Answer:
Internal Structure of Leaf: On basis of internal structure leaf has been divided into three types

• Bifacial or dorsiventral leaves: The leaves which possess distinct dorsal and ventral surfaces are called dorsiventral. The palisade is usually present below the upper epidermis.
• Unifacial leaves: The leaves which do not show any distinction of upper and lower surfaces are called unifacial. Example, cylindrical leaves of Allium.
• Isobilateral or Equifacial leaves: The leaves in which the upper and lower surfaces are similar, are called Equifacial. The mesophyll is generally not differentiated into palisade and spongy parenchyma or, if differentiated, the palisade is present on both the sides.
  Detailed structure of a part of T.S of maize Leaf
  Detailed structure of a part of T.S. of mango leaf.
  Three dimensional structure of some part of a dicot leaf (Various parts in different section)

Question 4.
Differentiate between internal structure of Dicot and monocot stem?
Answer:

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