RBSE Class 11 Biology Important Questions Chapter 6 Anatomy of Flowering Plants

Rajasthan Board RBSE Class 11 Biology Important Questions Chapter 6 Anatomy of Flowering Plants Important Questions and Answers.

RBSE Class 11 Biology Chapter 6 Important Questions Anatomy of Flowering Plants

Multiple Choice Questions

Question 1.    
Root hairs develop from the region of:
(a) maturation
(b) elongation
(c) root cap
(d) meristematic activity
Answer:
(d) meristematic activity

Question 2.    
Identify the wrong statement in context of heartwood
(a) organic compounds are deposited in it
(b) It is highly durable
(c) It conducts water and minerals efficiently
(d) It comprises dead elements with highly lignified walls
Answer:
(c) It conducts water and minerals efficiently

Question 3.    
Which of the following is made up of dead cells?
(a) Xylem parenchyma
(b) Collenchyma
(c) Phellem
(d) Phloem
Answer:
(c) Phellem

Question 4.    
The vascular cambium normal gives rise to:
(a) Phelloderm    
(b) Primary phloem
(c) Secondary xylem    
(d) Periderm
Answer:
(c) Secondary xylem    

Question 5.    
Specialised epidermal cells surrounding the guard cells are called:
(a) subsidiary cells    
(b) bulliform cells 
(c) lenticels    
(d) complementary cells
Answer:
(a) subsidiary cells    

Question 6.    
The balloon - shaped structures called tyloses:
(a) originate in the lumen of vessels
(b) characterise the sapwood
(c) are extensions of xylem parenchyma cells into vessel
(d) are linked to the ascent of sap through xylem vessels
Answer:
(c) are extensions of xylem parenchyma cells into vessel

Question 7.    
Cortex is the region found between:
(a) epidermis and stele
(b) pericycle and endodermis
(c) endodermis and pith
(d) endodermis and vascular bundle
Answer:
(a) epidermis and stele

Question 8.    
Read the different components from I - IV in the list given below and tell the correct order of the components with reference to their arrangement from outer side to inner side in a woody dicot stem.
I. Secondary xylem    
II. Wood
III. Secondary phloem 
IV. Phellem
The correct order is:
(a) III, IV, II, I    
(b) I, II, IV, III
(c) IV, I, III, II    
(d) IV, III, I, II
Answer:
(c) IV, I, III, II

Question 9.    
You are given a fairly old piece of dicot stem and a dicot root. Which of the following anatomical structures will you use to distinguish between the two?
(a) Secondary xylem    
(b) Secondary phloem
(c) Protoxylem    
(d) Cortical cells
Answer:
(c) Protoxylem

Question 10.    
Tracheids differ from other tracheary elements in:
(a) having casparian strips
(b) being imperforate
(c) lacking nucleus
(d) being lignified
Answer:
(b) being imperforate

Question 11.    
Interfascicular cambium develops from the cells of:
(a) medullary rays    
(b) xylem parenchyma
(c) endodermis    
(d) pericycle
Answer:
(a) medullary rays    

Question 12.    
Age of a tree can be estimated by:
(a) its height and girth
(b) biomass
(c) number of annual rings
(d) diameter of its heartwood
Answer:
(c) number of annual rings

Question 13.    
The common bottle cork is a product of:
(a) dermatogen    
(b) phellogen
(c) xylem    
(d) vascular cambium
Answer:
(b) phellogen

Question 14.    
Companion cells are closely associated with:
(a) seive elements 
(b) vessel elements
(c) trichomes
(d) guard cells
Answer:
(a) seive elements 

Question 15.    
Water containing cavities in vascular bundles are found in:
(a) sunflower    
(b) maize
(c) cycas    
(d) pinus
Answer:
(b) maize

Question 16.    
Closed vascular bundles lack:
(a) ground tissue    
(b) conjunctive tissue
(c) cambium    
(d) pith
Answer:
(c) cambium

Question 17.    
The cork cambium, cork and secondary cortex are collectively called:
(a) phellogen    
(b) periderm
(c) phellem    
(d) phelloderm
Answer:
(b) periderm

Question 18.    
Ground tissue includes:
(a) all tissues except epidermis and vascular bundles
(b) epidermis and cortex
(c) all tissues internal to endodermis
(d) all tissues external to endodermis
Answer:
(a) all tissues except epidermis and vascular bundles

Question 19.    
The chief water conducting elements of xylem in gymosperms are:
(a) vessels    
(b) fibres
(c) transfusion tissue    
(d) tracheids
Answer:
(b) fibres

Question 20.    
Which one of the following is not a lateral meristem?
(a) Intrafascicular cambium
(b) Interfascicular cambium
(c) Phellogen
(d) Interactory meristem
Answer:
(d) Interactory meristem

Question 21.    
Heartwood differs from sapwood in:
(a) presence of rays and fibres
(b) absence of vessels and parenchyma
(c) having dead and non - conducting elements
(d) being susceptible to pests and pathogens
Answer:
(c) having dead and non - conducting elements

Question 22.    
Palisade perenchyma is absent in leaves of:
(a) sorghun    
(b) mustard
(c) soyabean    
(d) gram
Answer:
(a) sorghun

Question 23.    
Anatomically fairly old dicotyledonous root is distinguished from the dicotyledonous stem by:
(a) absence of secondary xylem
(b) absence of secondary phloem
(c) presence of cortex
(d) position of protoxylem
Answer:
(d) position of protoxylem

Question 24.    
The annular and spirally thickened conducting elements generally develop in the protoxylem when the root or stem is:
(a) maturing    
(b) elongating 
(c) widening    
(d) differentiating
Answer:
(c) widening

Question 25.    
In barley stem, vascular bundles are:
(a) open and scattered    
(b) closed and scattered
(c) open and in a ring    
(d) closed and radial
Answer:
(b) closed and scattered

Question 26.    
The length of different internodes in a culm of sugarcane is variable because of:
(a) shoot apical meristem
(b) position of axillary buds
(c) size of leaf lamina at the node below each internode
(d) intercalary meristem
Answer:
(d) intercalary meristem

Question 27.    
Vascular tissues in flowering plants develop from:
(a) phellogen    
(b) plerome
(c) periblem    
(d) dermatogen
Answer:
(b) plerome

Question 28.    
Passage cells are thin walled cells found in:
(a) endodermis of roots facilitating rapid transport of water from cortex to pericycle
(b) Phloem elements that serve as entry points for substances for transport to other plant parts
(c) testa of seeds to enable emergence of growing embryonic axis during seed germination
(d) central region of style through which the pollen tube grows towards the ovary
Answer:
(a) endodermis of roots facilitating rapid transport of water from cortex to pericycle

Question 29.    
For a critical study of secondary growth in plants which one of the following pair is suitable:
(a) sugarcane ans sunflower
(b) teak and pine
(c) deodar and tern
(d) wheat and maiden hair fern
Answer:
(b) teak and pine

Question 30.    
A common structural feature of vessel elements and sieve tube elements are:
(a) pores in lateral walls
(b) presence of P - protein
(c) enucleate condition
(d) thick secondary walls
Answer:
(a) pores in lateral walls

Question 31.    
In a woody dicotyledonous tree which of the following parts will mainly consist of primary tissues:
(a) All parts
(b) Stem and root
(c) Flowers, fruits and leaves
(d) Shoot tips and roop tips
Answer:
(d) Shoot tips and roop tips

Question 32.    
In a longitudinal section of root, starting from the tip upward, the four zones occur in following order:
(a) root cap, cell division, cell enlargement, cell maturation 
(b) root cap, cell division, cell maturation, cell enlargement
(c) cell division, cell enlargement, cell maturation, root cap
(d) cell division, cell maturation, cell enlargement, root cap
Answer:
(a) root cap, cell division, cell enlargement, cell maturation 

Question 33.    
Chlorenchyma is known to develop in the;
(a) Pollen tube of pinus
(b) Cytoplasm of chlorella
(c) Mycelium of a green mould such as Aspergillus
(d) Spore capsule of a moss
Answer:
(d) Spore capsule of a moss

Question 34.    
The apical meristem of the root is present:
(a) in all the roots
(b) only in radicals
(c) only in tap roots
(d) only in adventitious roots
Answer:
(a) in all the roots

Question 35.    
The cells of the quiescent centre are characterised by:
(a) dividing regularly to add to tunica
(b) having dense cytoplasm and prominent nuclei
(c) having light cytoplasm and small nuclei
(d) dividing regularly to add to the carpus
Answer:
(c) having light cytoplasm and small nuclei

Question 36.    
Main function of lenticel is:
(a) transpiration    
(b) guttation
(c) gaseous exchange 
(d) bleeding
Answer:
(c) gaseous exchange

Question 37.    
Vessels are found in:
(a) all angiosperms and some gymnosperms
(b) most of angiosperms and few gymnosperms
(c) all angiosperms and few gymnosperms and some pteridophytes
(d) all pteriodophytes
Answer:
(b) most of angiosperms and few gymnosperms

Question 38.    
Four radial vascular bundles are found in:
(a) dicot root    
(b) monocot root
(c) dicot stem    
(d) monocot stem
Answer:
(a) dicot root

Question 39.    
Axillary bud and terminal bud are derived from the activity of:
(a) lateral meristem
(b) intercalary meristem
(c) apical meristem
(d) parenchyma
Answer:
(c) apical meristem

Question 40.    
Which of the following statements is true?
(a) Vessels are multicellular with narrow lumen
(b) Tracheids are multicellular with narrow lumen 
(c) Vessels are unicellular with wide lumen
(d) Tracheids are unicellular with wide lumen
Answer:
(a) Vessels are multicellular with narrow lumen

Question 41.    
Loading of phloem is related to:
(a) increase of sugar in phloem
(b) elongatipn of phloem cell 
(c) separation of phloem parenchyma
(d) strengthening of phloem fibre
Answer:
(a) increase of sugar in phloem

Question 42.    
What happens during vascular/station in plants?
(a) Differentiation of procambium is immediately followed by development of secondary xylem and phloem
(b) Differentiation of procambium followed by the development of xylem and phloem
(c) Differentiation of procambium, xylem and phloem is simultaneous,
(d) Differentiation of procambium followed by the development of primary phloem and then by primary xylem
Answer:
(c) Differentiation of procambium, xylem and phloem is simultaneous

Question 43.    
Which of the following meristems is responsible for extrastelar secondary growth in dicotyledonous stem?
(a) Intrafascicular cambium
(b) Interfascicular cambium
(c) Intercalary meristem
(d) Phellogen
Answer:
(d) Phellogen

Question 44.    
A leaf primordium grows into the adult leaf lamina by means of:
(a) apical meristem
(b) lateral meristem
(c) marginal meristem
(d) at first by apical meristem and later largely by marginal meristem
Answer:
(d) at first by apical meristem and later largely by marginal meristem

Question 45.    
At maturity which of the following is enucleate?
(a) Sieve cell    
(b) Companion cell
(c) Palisade cell    
(d) Cortical cell
Answer:
(a) Sieve cell

Question 46.    
What is not true about sclereids?
(a) These are parenchyma cells with thickened lignified walls
(b) These are elongated and flexible with tapered ends
(c) These are commonly found in the shells of nuts and in the pulp of guava, pear, etc.
(d) These are also called the stone cells
Answer:
(d) These are also called the stone cells

Question 47.    
As the secondary growth takes place (proceeds) in the tree, thickness of:
(a) heartwood increases 
(b) sapwood increases 
(c) both increase    
(d) both remain constant
Answer:
(a) heartwood increases

Question 48.    
Procambium forms:
(a) only primary vascular bundles
(b) only vascular cambium
(c) only cork cambium 
(d) primary vascular bundles and vascular cambium
Answer:
(d) primary vascular bundles and vascular cambium

Question 49.    
Abnormal/anamalous secondary growth occurs in:
(a) dracaena    
(b) ginger
(c) wheat    
(d) sunflower
Answer:
(a) dracaena

Question 50.    
Bordered pits are found in:
(a) sieve cells    
(b) ginger
(c) companion cells    
(d) sieve tubewall
Answer:
(b) ginger

Very Short Answer Type Questions

Question 1. 
Define meristem.
Answer:
The tissue consisting of actively dividing cells located in specific regions of plant is called meristem.

Quesiton 2. 
Name the tissue which provides mechanical strength to the plant organs.
Answer:
Sclerenchyma.

Question 3. 
Indicate the location of cambium in a dicot stem.
Answer:
Intrafascicular, between xylem and phloem within each vascular bundle.

Question 4. 
Name any two types of sieve elements found in phloem.
Answer:
Sieve cells and seive tubes.

Question 5. 
What is the role of lenticels in plants?
Answer:
Lenticels are the minute pores in the bark which perform the function of gaseous exchange.

Question 6. 
Name the tissue represented by the jute fibres used in making ropes.
Answer:
Sclerenchyma.

Question 7. 
Name the main components of xylem.
Answer:
Tracheids, vessels, xylem parenchyma and xylem fibres.

Question 8. 
Give two examples of fruits having sclereids. 
Answer:
Pear and coconut.

Question 9. 
What forms the cambial ring in a dicot stem during the secondary growth?
Answer:
Interfascicular cambium and intrafascicular cambium units to form cambium ring. 

Question 10. 
Define closed vascular bundle.
Answer:
A vascular bundle without cambium is called close vascular bundle.

Question 11. 
Define open vascular bundle.
Answer:
A vascular bundle having cambium is called open vascular bundle.

Question 12. 
What category of a permanent plant cell is companion cell?
Answer:
Companion cell is a component of phloem which is a complex permanent tissue. It is a living cell with dense cytoplasm and prominent nucleus.

Question 13. 
What is the function of companion cell?
Answer:
Companion cells assist the seive tubes in the process of translocation of solutes.

Question 14. 
What type oftissue constitutes catyptrogen? 
Answer:
Meristematie tissue.

Question 15. 
Which tissue of the leaf contains the chloroplasts.
Answer:
Meristematie tissue.

Question 16. 
What is exarch condition?
Answer:
When protoxylem lies towards periphery and metaxylem towards centre in primary xylem then this condition is called exarch condition.

Question 17. 
Name the components of secondary xylem. 
Answer:
Tracheids, vessels, xylem parenchyma and xylem fibres.

Question 18. 
Which tissue of the leaf contains the chloroplasts?
Answer:
Mesophyll.

Short Answer Type Questions - I

Question 1. 
Define intercalary meristem.
Answer:
The meristem located in between the regions of permanent tissues mostly at the base of node, base of internode or base of the leaf is termed as intercalary meristem.

Question 2. 
What is palisade parenchyma?
Answer:
Tissue consisting of thin walled, living, green, photo synthetic columner cells which lie vertically elongated just below the upper epidermis of leaves is called palisade parenchyma.

Question 3. 
Define meristematie tissue.
Answer:
A group of cells which are in continuous state of division and new cells of the plant body is called meristematie tissue.

Question 4. 
Where are companion cells located in flowering plants. Mention their function.
Answer:
Companion cells are the components of phloem and located alongwith the seive tubes. They help seive tubes in the translocation of solutes.

Question 5. 
Mention two differences between the vascular bundles of monocot and dicot stems.
Answer:

• Vascular bundles of dicots are open whereas those of monocots are closed.
• Vascular bundles of monocots are surrounded by bundle sheath whereas those of dicots are not.

Question 6. 
On the basis of vascular bundles give any two differences between monocot stem and dicot root. 
Answer:
Vascular bundles of monocot stem are conjoint, collateral and endarch. The vascular bundles of monocot root are radial and exarch.

Question 7. 
State the differences between the function of collenchyma and aerenchyma.
Answer:
Collenchyma acts as a chief supporting tissue in young dicotyledonous stem whereas aerenchyma provides buoyancy and gaseous exchange in aquatic plants.

Question 8. 
Why are mechanical tissues lacking in hydrophytes?
Answer:
Hydrophytes do not require much internal support to resist the stress and strains. Therefore, mechanical tissues are lacking in hydrophytes.

Question 9. 
What is an annual ring?
Answer:
The two bands in secondary xylem i.e., autumn wood and spring wood, produced in one year is called an annual ring.

Question 10. 
Name a plant organ where endodermis is absent. Give one basic difference between endodermis and epidermis.
Answer:
Endodermis is absent in leaves. Cells of endodermis passes casparian strips or bands in their radial and transverse walls whereas epidermal cells do not.

Short Answer Type Questions - II

Question 1. 
Why a large number of stomata are present at the lower surface of the dicotyledonous leaves in the terresterial plants?
Answer:
Dicotyledonous leaves are generally dorsiventral having distinct dorsal and ventral surfaces. The spongy parenchyma is located towards the lower side so that stomata are mostly present at the lower surface to help in gasebus exchange.

Question 2. 
What are medullary rays and what are their functions?
Answer:
Medullary rays are radially arranged living cells present between the xylem and phloem. They form the radial system responsible for radial conduction of solutes. They maintain connection between pith and cortex.

Question 3. 
Why there is secondary growth in dicots and no such growth in monocots?
Answer:
Dicotyledons possess cambium in their vascular bundles i.e., the vascular bundles are open. On the otherhand monocotytedons have no cambium in their vascular bundles. Therefore, secondary growth occurs in dicotyledons and not in monocotyledons.

Question 4. 
What is collenchyma? Explain its structure and function in a herbaceious angiosperm plant. 
Answer:
Collenchyma: The collenchyma occurs in layers below the epidermis in most of the dicotyledonous plants. It is found either as a homogeneous layer or in patches. It consists of cells which are much thickened at the corners due to a deposition of cellulose, hemicellulose and pectin. Collenchymatous cells may be oval, spherical or polygonal and often contain chloroplasts. These cells assimilate food when they contain chloroplasts. Intercellular spaces are absent. They provide mechanical support to the growing parts of the plant such as young stem and petiole of a leaf.

angiosperm, also called flowering plant, any of about 300,000 species of flowering plants, the largest and most diverse group within the kingdom Plantae. Angiosperms represent approximately 80 percent of all the known green plants now living. The angiosperms are vascular seed plants in which the ovule (egg) is fertilized and develops into a seed in an enclosed hollow ovary. The ovary itself is usually enclosed in a flower, that part of the angiospermous plant that contains the male or female reproductive organs or both. Fruits are derived from the maturing floral organs of the angiospermous plant and are therefore characteristic of angiosperms. By contrast, in gymnosperms (e.g., conifers and cycads), the other large group of vascular seed plants, the seeds do not develop enclosed within an ovary but are usually borne exposed on the surfaces of reproductive structures, such as cones.

Unlike such nonvascular plants as the bryophytes, in which all cells in the plant body participate in every function necessary to support, nourish, and extend the plant body (e.g., nutrition, photosynthesis, and cell division), angiosperms have evolved specialized cells and tissues that carry out these functions and have further evolved specialized vascular tissues (xylem and phloem) that translocate the water and nutrients to all areas of the plant body.

The specialization of the plant body, which has evolved as an adaptation to a principally terrestrial habitat, includes extensive root systems that anchor the plant and absorb water and minerals from the soil; a stem that supports the growing plant body; and leaves, which are the principal sites of photosynthesis for most angiospermous plants. Another significant evolutionary advancement over the nonvascular and the more primitive vascular plants is the presence of localized regions for plant growth, called meristems and cambia, which extend the length and width of the plant body, respectively. Except under certain conditions, these regions are the only areas in which mitotic cell division takes place in the plant body, although cell differentiation continues to occur over the life of the plant.

Question 5. 
Describe the location of interfascicular cambium and formation of interfascicular cambium in a dicot stem.
Answer:
The cells of cambium found between primary phloem and primary xylem in dicot stems are the intra - fascicular cambium. The cells of the medullary rays adjacent to this intra - fascicular cambium turn meristematic, hence forming the inter-fascicular cambium. Consequently, a continuous ring of cambium takes form

Intrafascicular cambium is primary meristem. It develops from the procambium of the stem apex. It is located inside the open vascular bundles, between phloem and xylem patches. During secondary growth the derivatives are only secondary phloem and secondary xylem. So, intrafascicular cambium is situated inside the vascular bundles. Interfascicular cambium is secondary meristem. It develops from the parenchymatous cells of medullary rays. It is located between two consecutive vascular bundles. During secondary growth its derivatives are secondary phloem, secondary xylem and conjunctive tissue. Thus, option B is the correct answer.

Long Answer Type Questions

Question 1. 
Name three permanent tissue found in flowering plants. Write the functions of xylem and phloem.
Answer:
In simple words, the permanent tissues in a plant are those tissues that contain nondividing cells. The cells are also modified to perform specific functions in the plants.  The cells of the permanent tissue are derived from the meristematic tissue.

The permanent tissue cells are also fully differentiated. The cells are large and a definite shape and size. You can see intercellular spaces being present in between the cells. Large vacuoles are also present inside these cells. The metabolism that occurs in the cells of the permanent tissue is fairly at a lower rate.

The permanent tissue in plants mainly helps in providing support, protection as well as in photosynthesis and conduction of water, minerals, and nutrients. Permanent tissue cells may be living or dead.
Permanent tissues can be classified into two types. They are:

• Simple permanent tissue
• Complex Permanent tissue

Xylem: Xylem functions as a conducting tissue for water and minerals from roots to the stem and leaves. It also provides mechanical strength to the plant parts. It is composed of four different kinds of elements, namely, tracheids, vessels, xylem fibres and xylem parenchyma. Gymnosperms lack vessels in their xylem. Tracheids are elongated or tube like cells with thick and lignified walls and tapering ends, These are dead and are without protoplasm. The inner layers of the cell walls have thickenings which vary in form. In flowering plants, tracheids and vessels are the main water transporting elements. Vessel is a long cylindrical tube - like structure made up of many cells called vessel members, each with lignified walls and a large central cavity.

The vessel cells are also devoid of protoplasm. Vessel members; are interconnected through perforations in their common walls. The presence of vessels is a characteristic feature of angiosperm. Xylem fibres have highly thickened walls and obliterated central lumens. These may either be septate or aseptate. Xylem parenchyma cells are living and thin walled, and their cell walls are made up of cellulose. They stores food materials in the form of starch or fat, and other substances like tannins. The radial conduction of water takes place by ray parenchymatous cells.

Primary xylem is of two types - protoxylem and metaxylem. The first formed primary xylem elements are called protoxylem and the later formed primary xylem is called metaxylem. In stems, the protoxylem lies towards the centre (pith) and the metaxylem lies towards the periphery of the organ. This type of primary xylem is called endarch. In roots, the protoxylem lies towards periphery and metaxylem lies towards the centre. Such arrangement of primary xylem is called exarch.

Phloem: Phloem transports food materials, usually from leaves to other parts of the plant. Phloem in angiosperms is composed of sieve tube elements, companion cells, phloem parenchyma and phloem fibres. Gymnosperms have albuminous cells and sieve cells. They lack sieve tubes and companion cells. Sieve tube elements are also long, tube - like structures, arranged longitudinally and are associated with the companion cells. Their end walls are perforated in a sieve - like manner to form the sieve plates.

A mature sieve element possesses a peripheral cytoplasm and a large vacuole but lacks a nucleus. The functions of sieve tubes are controlled by the nucleus of companion cells. The companion cells are specialised parenchymatous cells, which are closely associated with sieve tube elements. The sieve tube elements and companion cells are connected by pit fields present between their common longitudinal walls. The companion cells help in maintaining the pressure gradient in the sieve tubes.

Phloem parenchyma is made up of elongated, tapering cylindrical cells which have dense cytoplasm and nucleus. The ce,ll wall is composed of cellulose and has pits through which plasmodesmatal connections exist between the cells. The phloem parenchyma stores food material and other substances like resins, latex and mucilage. Phloem parenchyma is absent in most of the monocotyledons. Phloem fibres (bast fibres) are made up of sclerenchymatous cells. These are generally absent in the primary phloem but are found in the secondary phloem.

These are much elongated, unbranched and have pointed, needle like apices. The cell wall of phloem fibres is quite thick. At maturity, these fibres lose their protoplasm and become dead. Phloem fibres of jute, flax and hemp are used commercially. The first formed primary phloem consists of narrow sieve tubes and is referred to as protophloem and the later formed phloem has bigger sieve tubes and is referred to as metaphloem.

Question 2. 
Describe the tissue system in plants.
Answer:
We were discussing types of tissues based on the types of cells present. Let us now consider how tissues vary depending on their location in the plant body. Their structure and function would also be dependent on location. On the basis of their structure and location, there are three types of tissue systems. These are the epidermal tissue system, the ground or fundamental tissue system and the vascular or conducting tissue system.

The Epidermal Tissue System:
The epidermal tissue system forms the outer-most covering of the whole plant body and comprises epidermal cells, stomata and the epidermal appendages - the trichomes and hairs. The epidermis is the outermost layer of the primary plant body. It is made up of elongated, compactly arranged cells, which form a continuous layer. Epidermis is usually single - layered. Epidermal cells are parenchymatous with a small amount of cytoplasm lining the cell wall and a large vacuole. The outside of the epidermis is often covered with a waxy thick layer called the cuticle which prevents the loss of water. Cuticle is absent in roots. Stomata are present in the epidermis of leaves. Stomata regulate the process of transpiration and gaseous exchange.

Each stomata is composed of two bean- shaped cells known as guard cells which enclose stomatal pore. In grasses, the guard cells are dumb-bell shaped. The outer walls of guard cells (away from the stomatal pore) are thin and the inner walls (towards the stomatal pore) are highly thickened. The guard cells possess chloroplasts and regulate the opening and closing of stomata. Sometimes, a few epidermal cells, in the’ vicinity of the guard cells become specialised in their shape and size and are known as subsidiary cells. The stomatal aperture, guard cells and the surrounding subsidiary cells are together called stomatal apparatus (Figure 6.4).

The cells of epidermis bear a number of hairs. The root hairs are unicellular elongations of the epidermal cells and help in absorb water and minerals from the soil. On the stem the epidermal hairs are called trichdmes. The trichomes in the shoot system are usually multicellular. They may be branched or unbranched and soft or stiff. They may even be secretory. The trichomes help in preventing water loss due to transpiration.

The Ground Tissue System:
All tissues except epidermis and vascular bundles constitute the ground tissue. It consists of simple tissues such as parenchyma, collenchyma and sclerenchyma. Parenchymatous cells are usually present in cortex, pericycle, pith and medullary rays, in the primary stems and roots. In leaves, the ground tissue consists of thin - walled chloroplast containing cells and is called mesophyll.

The Vascular Tissue System:
The vascular system consists of complex tissues, the phloem and the xylem. The xylem and phloem together constitute vascular bundles (Figure 6.5). In  dicotyledonous stems, cambium is present between phloem and xylem. Such vascular bundles because of the presence of cambium possess the ability to form secondary xylem and phloem tissues, and hence are called open vascular bundles. In the monocotyledons, the vascular bundles have no cambium present in them.

Hence, since they do not form secondary tissues they are referred to as closed. When xylem and phloem within a vascular bundle are arranged in an alternate manner along the different radii, the arrangement is called radial such as in roots. In conjoint type of vascular bundles, the xylem and phloem are jointly situated along the same radius of vascular bundles. Such vascular bundles are common in stems and leaves. The conjoint vascular bundles usually have the phloem located only on the outer side of xylem.

Question 3. 
Draw neat labelled diagrams of a cross section of dicot and monocot roots.
Answer:

Question 4. 
Describe secondary growth in a dicot root. 
Answer:
In the dicot root, the vascular cambium is completely secondary in origin. It originates from the tissue located just below the phloem bundles, a portion of pericycle tissue, above the protoxylem forming a complete and continuous wavy ring, which later becomes circular (Figure 6.13). Further events are similar to those already described above for a dicotyledon stem.

Secondary growth also occurs in stems and roots of gymnosperms. Howevr, secondary growth does not occur in monocotyledons. 

Question 5.
Describe the process of secondary growth in a dicot stem.
Answer:
The growth of the roots and stems in length with the help of apical meristem is called the primary growth. Apart from primary growth most dicotyledonous plants exhibit an increase in girth. This increase is called the secondary growth. The tissues involved in secondary growth are the two lateral meristems: vascular cambium and cork cambium.