Rajasthan Board RBSE Class 11 Biology Chapter 13 Plant Tissue: Internal Morphology and Anatomy
RBSE Class 11 Biology Chapter 13 Multiple Choice Objective Questions
Question 1
Which characteristic is not found in meristematic cells –
(a) Unclear nucleus
(b) Dense protoplasm
(c) Divisonal cells
(d) Nondivisonal cells
Question 2.
Protoderm forms which part of plant tissue ?
(a) Vascular tissue
(b) Epidermis
(c) Ground tissues
(d) Lactiferous vessels
Question 3.
Intercalary meristem is present –
(a) Meristematic zone
(b) In between permanent tissues
(c) In lateral
(d) In apical
Question 4.
Root cap is formed by –
(a) Periblem
(b) Pleorome
(c) Tunica
(d) calyptrogen
Question 5.
Sclerenchymatous dies slowly and slowly why ?
(a) Deposition of cellulose
(b) Deposition of pectin
(c) Deposition of lignin
(d) Deposition of silica
Question 6
Gymnospcrm and Pteridophytes do not contain –
(a) Seive tubes / plates
(b) Wood fibres
(c) Wood parenchyma
(d) Companion cells
Question 7.
When we break aak tree, liquid comes out is –
(a) Latex
(b) Gum
(c) Tannin
(d) Resin
Question 8.
Oil glands are found in –
(a) Beetle leaf
(b) Deodar
(c) Lemon
(d) Babool
Question 9.
Glandular hairs are –
(a) Internal secretory cells
(b) External secrotory or external excretory cells
(c) Hydrathodes
(d) Gum glands
Question 10.
Aerenchyma is found in –
(a) Hydrophytes
(b) Xerophytes
(c) Halophytes (plants growing in salt)
(d) In all plants
Answers:
1. a, 2. b, 3. b, 4. d, 5. c, 6. d, 7. a, 8. c, 9. b, 10. a
RBSE Class 11 Biology Chapter 13 Very Short Answer Questions
Question 1.
Which plant parts are observed under plant anatomy?
Ans: Root, stem and leaf
Question 2.
Meristematic tissue are divided into how many types on basis of plane of division ?
Answer:
On the basis of cell division, meristem are divided as
(i) Mass meristem-
- Cells of this tissue divides in all direction.
- These tissues form cells which are unspecified such as embryosac
(ii) Plate meristem-
- These cells form plate like structure by periclinal and anticlinal plane of division.
- This meristems form single layer of unseriate. Outer epidermis and mulilayer cells in leave
(iii) Rib meristem-
- This meristem divide by anticlinal division and form longitudional axis and form sap of stem and root.
Question 3.
Apical meristem is found in which part or organs of plants ?
Answer:
Located in growing aspects of main and lateral shoots and roots.
Question 4.
Corpus is situated at what place of plants ?
Answer:
Forms central portion in apex
Question 5.
What is calyptrogen?
Answer:
The root cap is derived from a separate layer of initials called calyptrogen.
Question 6.
Where is Korper and kappe found ?
Answer:
Root apex.
Question 7.
At the loss of divisional property of meristematic cells which cells are formed ?
Answer:
Meristematic cells form permanent tissues.
Question 8.
What is the role of Chlorenchyma tissue ?
Answer:
Photosynthesis.
Question 9.
What does special tissues do ?
Answer:
These tissues perform special function in the plants e.g., secretion of resin gum, oil and latex.
Question 10.
How many types of pits are there ?
Answer:
Simple and Bordered pits.
RBSE Class 11 Biology Chapter 13 Short Answer Questions
Question 1.
What are the functions of protoderm?
Answer:
It produces epidermal tissue system.
Question 2.
What is the difference in direction of division of tunica and corpus ?
Answer:
Tunica cells divide by anticlinal division and corpus divide in all planes.
Question 3.
What is the difference in base division of corpus and cap ?
Answer:
Tunica Corpus Theory:
This theory was proposed by Schmidt (1924) According to this theory, the shoot apex consists of two distinct zones-
(i) The outer tunica, which surrounds and envelops:
Tunica consists of one or more peripheral or outer layer of cells. These cells are comparatively smaller and divide by anticlinal divisions i.e.with the axis of mitotic spindleparalled to the surface. Thus the cross walls separating the two daughter cells are formed perpendicular to the surface so that the number of layers do not increase. Cells derived from tunica differentiate into epidermis
(ii) The inner corpus. which forms the central core:
The corpus occupies the central portion in which the cells arc comparatively larger. These cells divide in all the planes. These cell form the procambium and ground meristem. Procambium gives risc to pr mary xylem, primary phloem and intrafascicular cambium. The ground men stem forms the ground tissue (i.e. cortex, endodermis, penicycle and pith).
(B) Root Apex :
A group of initial cells, present at the subterminal region of the growing root tip, which is protected by a root cap is called root apical meristem or root apex.
- It is embryonic in origin and formed from the radicle part of embryo.
- In adventitious roots it is produced from derivatives of root appex.
- The root apex is short as compared to shoot apex. It is more or less uniform due to complete absence of lateral.
- Appendages (leaves and branches) and differentiation of nodes and intemodes.
- Cell division in the apical meristem adds new cells both to the body of the root and to the root cap.
- Histogen theory of Hanstein (1870), the root apex of most of the dicotyledons consists of three meristematic zones or layers –
- Plerome forms pith, vascular strands and pericycle,
- Periblem forms endodermis and cortex and
- Dermatocalyptrogen gives rise to protoderm as well as the root cap.
- The theory believes that in monocotyledons, the root cap is derived from a separate layer of initials called calyptrogen and the protoderm is derived from dermatogen. Periblem is derived from dermatogen.
- In addition to actively dividing cells, a zone of inactive cells is present in the central part of the root apex called quiescent centre (clowes, 1961). It is a central cap- like or hemispherical region of inactive cells present in between the root cap and the active meristematic region of root apex. This zone contains several hundred cells which are characterized by having lower concentration of DNA, RNA and protein. These cells also contain fewer number of mitochondria, less endoplasmic reticulum and small dictyosomes.
- The quiescent centre acts as reservoir of cells and becomes active whenever the initials get damaged or during the establishment of the secondary’roots. However, normally the cells of quiscent centre do not divide and remain inactive.
- Mainly in roots with a very regular arrangement of cells in the apical meristem, such as of Zea mays, it is possible to conclude form the study of cell lineages that there is a central region of cells which divide rarely or not at all. The cells on the periphery of this hemispherical or cup – shaped region are meristematic. This inactive or passive region of cells is known as ‘quiescent centre’.
Question 4.
many types of collenchyma are there ?
Answer:
Collenchyma :
Collenchyma (Greek, colla = glue; enchyma an infusion) is the tissue of primary body. The cells of this tissue contain protoplasm and are living. The cell walls show localized thickenings due to presence of approximately 45% pectin, 35 % hemicellulose and 20 % cellulose.
They are never lignified but may possess simple pits. Presence of cellulose and pectic substances in the cell wall accounts for the high water absorbing capacity to the cells. The tissue is plastic, extensible and has capacity to expand and gives a tensile strenth to the organ. Originates from elongated cells that resemble procambium.
Thus, the cells are generally elongated with oblique end walls. Sometimes the ends may be rounded. They occure chiefly in the hvpodermis of dicotyledonous stems (e.g. cucurbita, helianthus) and leaves. They are usually absent in monocots and in roots. However, they may occur in root cortex if the root is exposed to light.
Functions of Collenchyma:
- It is the chief supporting tissue in young dicotyledonous stems.
- Has capacity to expand and gives a tensile strength to the body.
- It is present at the margins of some leaves and resists tearing effect of the wind.
- Some cells possess chloroplasts and perform photosynthesis.
Question 5.
What is the difference between Sclerenchymatous fibres and sclereids ?
Answer:
S.No | Property | Fibres | Sclereids |
1. | Shape and structure | Long cells with tapering ends | Comparatively shorter in size |
2. | Presence of pits and their number | Wall possess simple and oblique pits. The pits are less in number | Wall possess simple and tubular pits. Presence of numerous pits |
3. | Origin | Originate from meristematic cells |
Originate from ordinary parenchvmetion cells by deposition of lignified second- dary walls |
Question 6.
What is the difference between tracheids and vessels in xylem ?
Answer:
S.No | Property | Tracheids | Vessels |
1. | Plants containing them | In all vascular elements(Pteri – dophytes, gymno – sperm and angio – sperms) | Found mainly in angiosperms. Also in some pterido- phytes (e.g sela- ginella, Equisetum and pteridium) and gymnosperms (eg Gnetales) |
2. | Length | Comparatively short and rarely exceed 1 mm in length | Usually long and may attain 10 cm in length. Rarely reach to 2-6 metres (Quercus, Eucalyptus) |
3. | Shape | Elongated with tapering ends end wall remains intact. | Cells placed one upon the other and their end walls are either absent or possess perforation |
4. | Cell cavities | Not much wide | Wide as compared to tracheids. |
Question 7.
What is the difference between Sieve tubes and companion cells ?
Answer:
(i) Sieve Elements (Plate and Sieve areas):
There is a presence of sieve plate and sieve areas in sieve elements.
- Groups of pores present in the walls of sieve elements are called sieve areas. In a sieve cell, these areas are generally located in lateral walls whereas in sieve-tube element. These areas are located in the cross-walls (end walls).
- The portion of cross-wall possessing sieve areas is called sieve plate.
- In most of the angiosperms the sieve plate is single and present in the transverse or oblique end wall (eg. Cucurbita.Nicotiana, etc) It is called simple sieve plate.
- In some of the cases, there are many sieve areas in the end walls. These are termed as compound sieve plates.
- The nucleus disappears in mature sieve elements.
Function of Sieve elements:
- Translocation of organic solutes. This is achieved by their special anatomical features. The sieve tubes are syncytes (formed by the fusion of cells) and allow free diffusion of soluble organic substances.
- The callose also plays important role. Usually the perforations in the sieve plates ae surrounded by callose. The callose is soluble and disappears when the solute is dilute so that the solute can pass from one cell to another cell through the pores. The callose reappears and sometimes closes the pores when solute is less dilute stopping the movement.
(ii) Companion cells:
- These are living cells, usually always associated with the sieve tubes.
- In primary phloem the companion cell is formed by unequal longitudinal division or procambial cell.
- Thus single companion cell is usually associated with each sieve tube element. Sometimes, there may be more (e g. Carrot).
- Each companion cell is a living cell with thin cellulose cell wall and active protoplast.
- It possesses all the important cellular contents viz. nucleus, mitochondria, endoplasmic reticulum, dictyosomes, plastids, ribosomes, etc.
- The cytoplasm is compartmentalized due to presence of membrane system. It also contains slime bodies. The common wall between companion cell and sieve tube shows presence of fine pits which are transverse by plasmodesmata.
- The companion cells are absent in pteridophytes and gymnosperms. They are present in angiosperms (both in monocots and dicots).
- They assist the sieve tubes in the process of translocation of solutes. .
Question 8.
How many different types of wall thickenings are present in tracheids ?
Answer:
The term xylem (Greek, xylos = wood) was introduced byNageli (1858). Chief conducting tissue of vascular plants responsible for conduction of water and inorganic solutes.
Components of Xylem
(i) Tracheids :
Tracheids are elongated tube like dead cells (without protoplasm) with tapering ends (tangenital section)
They appear elongated (tangenital section) rectangular or somewhat rounded (radial section), angular or polygonal (cross section) but in some cases they may appear rounded. The walls are hard and lignified but not much thick and enclose a wide empty lumen. The tracheids are long but not as long as fibres. They reach up to 1 mm in length (in some plants they may attain a length of 12 cm or more).
The tracheids of primary xylem developes from pro-cambium whereas those of secondary xylem developes from vascular cambium. In the beginning these cells possess living protoplasm but due to lignification and deposition of thickening materials in wall they become dead at maturity.
Wall thickenings in Tracheids :
Tracheids possess various types of wall thickenings viz – annular, spiral, scalariform, reticulate and pitted. The protoxylem tracheids have annular (ring-.like) and spiral (helical) thickenings. The metaxylem and secondary xylem tracheids have scalariform (ladder like), reticulate (network) and pitted thickenings. The pits are of two types simple or bordered. The size and number of pits vary greatly in each tracheid.
Functions of Tracheids:
- To conduct water and dissolved mineral elements from roots to the leaves. They are structurally adapted to their specific function.They are placed one above the other and also parallel to the long axis. The end walls are perforated by the presence of bordered pits which permit flow of water from one cell to another.
- Also provide mechanical support due to presence of hard and firm secondary walls.
Question 9.
What is difference between simple and complex tissues?
Answer:
(a) Simple Tissue:
Simple tissue is made up of same type of cells and mostly cover the surface of both, internal organs of the body and external organs of the body. Simple tissue is tightly packed together. A simple tissue is called epithelium in animals and epidermis in plants. Example of simple tissue is muscle tissue.
(b) Complex Tissue:
Complex tissue is made up of different type of cells. The main purpose of complex tissue is to actually bind organs together and to support them. These tissues are scattered everywhere in the body. They are also known as connectivity tissue in animals and vascular tissue in plants. Example of complex tissue is blood tissue.
Question 10.
What is the difference between laticiferous cells and laticiferous vessels ?
Answer:
(1) Latex cells: They differ from latex vessels in that they are not formed due to cell fusions and with other latex cells to form a network. They are branched or unbranched. They do not anastamose eg. Calotropis, Nerium, Thevetia. Euphorbia (Fig A)
(2) Latex vessels: They are composed of a large number of cells placed end to end with their transverse walls dissolved so as to form a long vessels. They are unbranched in the beginning but get branched later. Two or more latex vessels fuse with each other forming a network eg. Papaver, Argemone, Sonchus.(B)
RBSE Class 11 Biology Chapter 13 Essay Type Questions
Question 1.
Explain different theories with diagram in relation to organisation of shoot apex and root apex ?
Answer:
Shoot Apex:
The terminal meristem present at the apices of stem and its branches is called shoot apex. Formed either at the plumular tip of the embryo or in the axil of a leaf. Lies immediately above the uppermost primordial leaf. Radially symmetrical and appears like a cone with rounded (or convex) apex. Varies in shape and size in different plants or in different branches of the same plant. Not protected by any cap.
However it is protected by the overarching young leaves and often by bud scales. Cell division in the apical meristem continuously adds new cells to stern beneath it. Growth in the shoot apex is not uniform due to presence of leaves, nodes and internodes.
The apex shows alternating broad and narrow zones due to formation of leaf pnmordia which occur at regular intervals and in rctular nattern. (A leaf orimordiurn is on the flank of the apex. It results in the broadening of the apex at this region, The apex becomes narrow again after the formation of leaf primordium).
The interval between the two successive leaf primordia is called plastochron. Several theories have been put forward to describe the structure and organisation of shoot apex. These include
- Apical cell theory
- Histogen theory
- Tunica corpus theory, mantle-core hypothesis, etc.
Apical Cell Theory :
According to this theory, shoot apical meristem consists of single apical cell (Nageli, 1858)
Single apical cell leads to the development of entire plant body. This theory is applicable in case of higher algae, bryophytes and in many pteridophytes. Not applicable to higher plants (i.e. gymnosperms and angiosperms). This theory supported by Hofmeister.
Histogen Theory : This theory was proposed by Hanstein (1870) According to this theory, the shoot apical meristem consists of three distinct meristematic zones or layers (or histogens).
- Dermatogen (external layer) forms the outer covering in all organs of the plant i.e epidermis,
- Periblem (middle layer) gives rise to cortex and endodermis, and
- Plerome (the central core) forms the pith and primary vasular tissue.
Haberlandt (1914) proposed the name protoderm for dermatogen, ground meristem for periblem and procamium for plerome.
Tunica Corpus Theory: This theory was proposed by Schmidt (1924) According to this theory, the shoot apex consists of two distinct zones-
(i) The outer tunica, which surrounds and envelops:
Tunica consists of one or more peripheral or outer layer of cells. These cells are comparatively smaller and divide by anticlinal divisions i.e.. with the axis of mitotic spindle paralled to the surface. Thus the cross walls separating the two daughter cells are formed perpendicular to the surface so that the number of lay ers do not increase. Cells derived from tunica differentiate into epidermis
(ii) The inner corpus, which forms the central core:
The corpus occupies the central portion in hich the cells are comparatively larger.These cells divide in all the planes. These cell form the procambium and ground meristem. Procambium gives rise to pr mar xylem, primary phloem and intrafascicular cambium. The ground meristem forms the ground tissue (i.e. cortex, endodermis, pericycle and pith).
Root Apex :
A group of initial cells, present at the subterminal region of the growing root tip, which is protected by a root cap is called root apical meristem or root apex. It is embryonic in origin and formed from the radicle part of embryo. In adventitious roots it is produced from derivatives of root appex. The root apex is short as compared to shoot apex. It is more or less uniform due to complete absence of lateral. Appendages (leaves and branches) and differentiation of nodes and intemodes. Cell division in the apical meristem adds new cells both to the body of the root and to the root cap.
Histogen theory of Hanstein (1870), the root apexof most of the dicotyledons consists of three meristematic zones or layers –
- Plerome forms pith, vascular strands and pericycle,
- Periblem forms endodermis and cortex and
- Dermatocalyptrogen gives rise to protoderm as well as the root cap.
The theory believes that in monocotyledons, the root cap is derived from a separate layer of initials called calyptrogen and the protoderm is derived from dermatogen.
In addition to actively dividing cells, a zone of inactive cells is present in the central part of the root apex called quiescent centre (clowes, 1961). It is a central cap- like or hemispherical region of inactive cells present in between the root cap and the active meristematic region of root apex. This zone contains several hundred cells which are characterized by having lower concentration of DNA, RNA and protein.
These cells also contain fewer number of mitochondria, less endoplasmic reticulum and small dictyosomes. The quiescent centre acts as reservoir of cells and becomes active whenever the initials get damaged or during the establishment of the secondary’roots. However, normally the cells of quiscent centre do not divide and remain inactive.
Mainly in roots with a very regular arrangement of cells in the apical meristem, such as of Zea mays, it is possible to conclude form the study of cell lineages that there is a central region of cells which divide rarely or not at all. The cells on the periphery of this hemispherical or cup – shaped region are meristematic. This inactive or passive region of cells is known as ‘quiescent centre’.
Root apex: pattern of cell lineages in the root apex of Zea mays the cortex,vascular cylinde of stem, root cap quiescent center are indicated.
Question 2.
What are simple tissues? Describe salient features and functions of meristematic tissue ?
Answer:
These tissues are composed of similar type of cells which have common origin and function. They are further grouped under three categories parenchyma, collenchyma and sclcrenchyma.
(i) Parenchyma:
Parenchyma (Greek, para = beside; en – chein = to pour) is most simple and unspecialized tissue which is concmed mainly with the ordinary vegetative activities of the plant. It is phylogenetically and ontogenctically the primitive tissue. The tissue mainly consists of thin walled living cells which have intercellular spaces between them The cell wall is made of cellulose or calcium pectate. Possesses a prominent nucleus and vacuolate cytoplasm.
The intercellular spaces are either formed schizogenously (i.e by splitting apart of the middle lamellae region between cells) or lysigenously. However, they remain attached by plasmodesmata. Sometimes the intercellular spaces are absent.b Each individual parenchymatous cell may be spherical, oval, cylindrical, rectangular, stellate or long spindle like. It is that cells varies in different plants and in different organs of the same plant.
Parenchyma is distributed in almost all the parts of plant body constitutiong the vegetative ground tissue. It is found in epidermis, cortex, pith, pericycle, mesophyll of leaves, pulp of fruits, endosperm of seeds and in meristematic tissues. Parenchymatous cells are also found in xylem and phloem.
Functions of Parenchyma: Parenchymatous tissue performs the following functions in different plant organs –
- Storage of reserve food materials.
- Storage of water in succulents, (e.g., Opuntia, Euphorbia)
- Buoyancy and gaseous exchange in water plants. (Aerenchyma).
- Provide rigidity to plant body due to turgidity and help to maintain the shape of plant body.
- They give rise to secondary meristem in the form of cork cambium and vasular cambium, (secondary growth and healing)
- They perform all vital activities of plants.
- Sometimes develop chloroplasts and called as chlorenchyma and take part in photosynthesis.
(ii) Collenchyma:
Collenchyma (Greek, colla = glue; enchyma an infusion) is the tissue of primary body. The cells of this tissue contain protoplasm and are living. The cell walls show localized thickenings due to presence of approximately 45% pectin, 35 % hemicellulose and 20 % cellulose. They are never lignified but may possess simple pits. Presence of cellulose and pectic substances in the cell wall accounts for the high water absorbing capacity to the cells. The tissue is plastic, extensible and has capacity to expand and gives a tensile strenth to the organ.
Originates from elongated cells that resemble procambium. Thus, the cells are generally elongated with oblique end walls. Sometimes the ends may be rounded. They occure chiefly in the hvpodermis of dicotyledonous stems (e.g. cucurbita, helianthus) and leaves. They are usually absent in monocots and in roots. However, they may occur in root cortex if the root is exposed to light.
Functions of Collenchyma:
- It is the chief supporting tissue in young dicotyledonous stems.
- Has capacity to expand and gives a tensile strength to the body.
- It is present at the margins of some leaves and resists tearing effect of the wind.
- Some cells possess chloroplasts and perform photosynthesis.
Sclereids:
The sclerenchvmatous cells, which are short and possess extremely thick lamellated lignified waIls with long tubular simple pits are called sciereids. They originate from ordinary parenchymatous cells by the deposition of secondary wall layers. The’ mas’ be simple or branched. The sciereids vary greatly in their shape and size. they may be spherical, oval, cylindrical, T shaped, dumbell – shaped or even stellate. They are usually shorter than fibers.
Question 3.
Describe common salient features of meristematic tissues. On basis of origin and development they are divided into how many types ?
Answer:
Meristematic Tissues:
- Group of cells that are preparing to divide or are in continuous state of division or have the capacity to
divide. - In early embryonic stages all the cells are meristematic in nature but later on this activity of diyison get restricted to certain specific regions called meristem (meristem means = divisible).
- Meristemetic tissue are found in growing regions of plants and plants grow by these tissue.
(A) Based on origin and method of development meristems are of following three types.
1.Promeristem (= primordial meristem) –
- A group of cells originate from embryo end therefore called primordial or embryonic meristem.
- These tissue cells represent primary stages of meristemetic cells.
- These tissue are present in a small region at the apices of shoots and roots.
- Promeristem give rise to primary meristem.
2. Primary Meristem –
- The meristematie cells that originate from promeristem are primary meristems.
- These cells are always in active state of division and give rise to primary permanent tissues.
- They are present below the promeristem at shoot and root apices, at the apex of leaves and in intercalary parts.
- Protoderm (produces epidermal tissue system), procambium (produces primary vascular elements) ground meristem (produces cortex and pith) are kinds of primary meristem.
3. Secondary Meristem –
- They originate from primary permanent tissues.
- They do not have their own promeristem.
- Develop at a later stage and give rise to secondary permanent tissues.
- The cambium of root, vascular cambium (from interfascicular regions in dicots when secondary growth is needed and as cork cambium when formation of periderm and healing of wounds is needed.
S.No | Property | Primary Meristem | Secondary Meristem |
1. | Origin | Originates from promeriste or embryonic meristem of the plant | Developes os new meristem from permanent tissues due to de differentiation |
2. | Shape | Generall round, oval,polygonal and rectangular in shape. | Generally elongated |
3. | Central Vacuoles | Absent | Present |
4. | Form | They give rise to primary perma nent tissues of the primary body of plants In (rafascicular cambium is exception) | Give rise to secondary or supplementary tiss-ues of the plants |
5. | Examples | Protoderm, pro-cambimm and Ground meris tem | Vascular cambium (except intrafas- cicular cambium) |
Question 4.
Comment on structure, type and functions
(a) Collenchyma
(b) Sclerenchyma
Answer:
(i) Parenchyma:
Parenchyma (Greek, para = beside; en – chein = to pour) is most simple and unspecialized tissue which is concmed mainly with the ordinary vegetative activities of the plant. It is phylogenetically and ontogenctically the primitive tissue. The tissue mainly consists of thin walled living cells which have intercellular spaces between them The cell wall is made of cellulose or calcium pectate.
Possesses a prominent nucleus and vacuolate cytoplasm The intercellular spaces are either formed schizogenously (i.e by splitting apart of the middle lamellae region between cells) or lysigenously. However, they remain attached by plasmodesmata. Sometimes the intercellular spaces are absent. Each individual parenchymatous cell may be spherical, oval, cylindrical, rectangular, stellate or long spindle like. It is that cells varies in different plants and in different organs of the same plant.
Parenchyma is distributed in almost all the parts of plant body constitutiong the vegetative ground tissue. It is found in epidermis, cortex, pith, pericycle, mesophyll of leaves, pulp of fruits, endosperm of seeds and in meristematic tissues. Parenchymatous cells are also found in xylem and phloem.
Functions of Parenchyma :
Parenchymatous tissue performs the following functions in different plant organs –
- Storage of reserve food materials.
- Storage of water in succulents, (e.g., Opuntia, Euphorbia)
- Buoyancy and gaseous exchange in water plants. (Aerenchyma).
- Provide rigidity to plant body due to turgidity and help to maintain the shape of plant body.
- They give rise to secondary meristem in the form of cork cambium and vasular cambium, (secondary growth and healing)
- They perform all vital activities of plants.
- Sometimes develop chloroplasts and called as chlorenchyma and take part in photosynthesis.
(iii) Sclerenchyma:
Sclerenchyma (Greek, sclerous = hard; enchyma = an infusion) consists of thick – walled dead cells.Cells vary in shape, size and origin.They possess hard and extremely thick secondary walls due to uniform deposition of lignin . Sometimes, they may be unlignified. In the beginning the cells are living and have protoplasm, but due to deposition of impermeable secondary walls they become dead.
(b) Sclereids :
The sclerenchymatous cells, which are short and possess extremely thick lamellated lignified walls with long tubular simple pits are called sclereids. They originate from ordinary parenchymatous cells by the deposition of secondary wall layers. They may be simple or branched. The sclereids vary greatly in their shape and size, they may be spherical, oval, cylindrical, T shaped, dumbell – shaped or even stellate. They are usually shorter than fibers.
Question 5.
What are different types of vascular tissues? Write different components of it and explain any one in detail ?
Answer:
The term xylem (Greek, xylos = wood) was introduced by Nageli (1858). Chief conducting tissue of vascular plants responsible for conduction of water and inorganic solutes. Components of Xylem
(i) Tracheids :
Tracheids are elongated tube like dead cells (without protoplasm) with tapering ends (tangenital section)
They appear elongated (tangenital section) rectangular or somewhat rounded (radial section), angular or polygonal (cross section) but in some cases they may appear rounded. The walls are hard and lignified but not much thick and enclose a wide empty lumen. The tracheids are long but not as long as fibres. They reach up to 1 mm in length (in some plants they may attain a length of 12 cm or more).
The tracheids of primary xylem developes from pro-cambium whereas those of secondary xylem developes from vascular cambium. In the beginning these cells possess living protoplasm but due to lignification and deposition of thickening materials in wall they become dead at maturity.
Wall thickenings in Tracheids :
Tracheids possess various types of wall thickenings viz. – annular, spiral, scalariform, reticulate and pitted. The protoxylem tracheids have annular (ring-.like) and spiral (helical) thickenings. The metaxylem and secondary xylem tracheids have scalariform (ladder like), reticulate (network) and pitted thickenings. The pits are of two types simple or bordered. The size and number of pits vary greatly in each tracheid.
Functions of Tracheids:
- To conduct water and dissolved mineral elements from roots to the leaves. They are structurally adapted to their specific function.
- They are placed one above the other and also parallel to the long axis. The end walls are perforated by the presence of bordered pits which permit flow of water from one cell to another.
- Also provide mechanical support due to presence of hard and firm secondary walls.
(ii) Vessels (or Tracheae) :
The xylem vessel designates a long tube consisting of a series of drum-shaped cells placed one above the other with their end walls perforated or dissolved. The vessels are. thus, syncytes formed by fusion of cells. Each cell appears circular, oval or sometimes polygonal in cross section with a very wide lumen. They become dead and loose their protoplasm due to deposition of lignified secondary wall.
Vessels of primary xylem develop from pro cambium whereas those of secondary xylem develop from vascular cambium. They can also be derived by dissolution of end walls or pit membranes. Each cell is short but due to cell fusion the tube becomes much longer. It reaches upto 10 cm in length but in some cases it may reach up to 2 m (as in Quercus) or 3 – 6 m (as in Eucalyptus).
Wall thickenings in Vessels:
The most common ones wall thickenings are scalariform, reticulate and pitted. The protoxylem vessels possess annular and spiral thickening which later on become scalariform and reticulate due to deposition of more thickening materials. The metaxylem vessels generally possess simple pits. The vessels of secondary xylem also possess scalariform, reticulate and pitted thickenings. The pits may be simple or bordered.
Perforation plates:
The wall area bearing perforation is called perforation plate. Usually the perforations in vessels are present in the end walls but they may be present in the lateral walls too. The perforations may be simple (single perforation) or multiple (many perforations). The multiple perforations may be arranged in a row (Scalariform perdoration), in the form of net work (reticulate perforation) or in the form of groups of circular holes (foraminate perforation).
(iii) Xylem fibres (or wood fibres) :
The xylem fibres develop from the same meristematic tissue as the other xylem cells. They have lignified secondary walls and narrow cell xlumen. They are usually longer than the tracheids of the same plant and present both in primary as well as secondary xylem.
(iv) Xylem parenchyma :
These are living parenchymatous cells present as component of xylem both in primary as well as secondary xylem.
The parenchyma present in secondary xylem are of two types :
- Wood parenchyma and
- Ray parenchyma.
The wood parenchyma are formed from the fusiform cambial initials whereas ray parenchma are formed from ray initials of the cambium. Both the types have thin walls and living protoplasm. They help in conduction. The main function of xylem parenchyma is storage if fod reserves in the form of starch or fat.
Phloem:
Phloem is the chief food conducting tissue of vascular plants responsible for translocation of organic solutes. The phloem composed of several defferent kinds of cells. The basic components are
- Sieve elements,
- Companion cells,
- Phloem Parenchyma and
- Phloem fobres.
A fifth kind of cell type, the transfer cell, lias Recently been reported from the phloem. Though all the basic components of phloem occur in most of the vascular e&cftmature sieve element has thin or thick, cellulose wall surrounding a highly albuminous and viscous contents. Cytoplasm occurs in the form of thin lining enclosing a big central vacuole. The nucleus, plastids, mitochondria endoplasmic reticulum and dictyosomes are absent. The vacuole is filled with albuminous substances. Presence of leucoplasts has also been reported in the vacuole.
(i) Sieve Elements (Plate and Sieve areas):
There is a presence of sieve plate and sieve areas in sieve elements. Groups of pores present in the walls of sieve elements are called sieve areas. In a sieve cell, these areas are generally located in lateral walls whereas in sieve-tube element. These areas are located in the cross-walls (end walls).
The portion of cross-wall possessing sieve areas is called sieve plate. In most of the angiosperms the sieve plate is single and present in the transverse or oblique end wall (eg. Cucurbita.Nicotiana, etc) It is called simple sieve plate.
In some of the cases, there are many sieve areas in the end walls. These are termed as compound sieve plates.
The nucleus disappears in nature sieve elements.
Function of Sieve elements:
Translocation of organic solutes. This is achieved by their special anatomical features. The sieve tubes are syncytes (formed by the fusion of cells) and allow free diffusion of soluble organic substances. The callose also plays important role. Usually the perforations in the sieve plates are surrounded by callose. The callose is soluble and disappears when the solute is dilute so that the solute can pass from one cell to another cell through the pores. The callose reappears and sometimes closes the pores when solute is less dilute stopping the movement.
(ii) Companion cells:
These are living cells, usually always associated with the sieve tubes. In primary phloem the companion cell is formed by unequal longitudinal division or procambial cell. Thus single companion cell is usually associated with each sieve tube element. Sometimes, there may be more (e g. Carrot). Each companion cell is a living cell with thin cellulose cell wall and active protoplast.
It possesses all the important cellular contents viz.- nucleus, mitochondria, endoplasmic reticulum, dictyosomes, plastids, ribosomes, etc. The cytoplasm is compartmentalized due to presence of membrane system. It also contains slime bodies. The common wall between companion cell and sieve tube shows presence of fine pits which are transverse by plasmodesmata. The companion cells are absent in pteridophytes and gymnosperms. They are present in angiosperms (both in monocots and dicots). They assist the sieve tubes in the process of translocation of solutes. .
(iii) Phloem Parenchyma:
These are living parenchymatous cells present as component of phloem. The cells are elongated with rounded ends and possess cellulose cells walls. The phloem parenchyma are present in pteridophytes and most of the dicotyledonous angiosperms. They are absent in monocots and some of the dicots (Ranunculus). in active phloem, these cells remain active but as soon as the activity of sieve-tubes ceases they become lignified.The main function of phloem parenchma is translocation and storage of food reserves.
(iv) Phloem fibres:
These are also called bast fibers and mostly occur in secondary phloem. The fibers of primary phloem have both cellulose and lignified thickenings. The fibers of secondary phloem are elongated lignified cells with simple pits. The ends of these cells may be pointed needle like or blunt. They are non-living cells that provide mechanical support and give strength and rigidity to the organ.
Question 6.
What are different types of special tissues. Explain salient features and special tissues of each type?
answer:
special tissues:
These tissues perform special function in the plants e.g secretion of resin gum, oil and latex.
These tissues are of two types:
- Glandular tissue
- Laticiferous tissue.
Glandular tissues:
As the name indicates this tissue is present in the form of glands in or on various parts of plants. A gland is a specialized group of cells that are endowed with the capacity to secrete or excrete products. These are of two types:
- External glands,
- Internal glands.
1. External glands: They generally occur on the epidermis of stem and leaves as glandular outgrowth e.g glandular hair, nectar secreting and enzyme secreting glands.
(a) Glandular hair: These hair are present in epidermal layers of leaves and are of various kinds. They may be unicellular or multicellular. They are living e.g. Stinging hair on the under surface of Urtica dioica (Bichhu buti) is unicellular arising from lower epidermis of leaf. The walls of these hair are slicified, calcified and brittle. Contents of hair are poisonous and are secreted by a gland at the base of hair. When struck sharply the hair rupture the skin like hypodermic needle. The hair injects an albuminoid poison and causes irritation and blisters.
(b) Nectaries: Present in flowers or leaves. In Rutaccae they are found as a disc below the ovary. In Euphorbia pulcherrima the nectaries on the edge of involucere are composed of layer of elongated palisade like secrected cells. Cell walls of these cells are thin and the cells have dense cytoplasm.
(c) Digestive glands or Enzyme seereting glands: Insectivorous plants posssess the power of digesting proteins from bodies of insects by secreting some digestive enzymes by means of glands or glandular hair e.g drosera (sundew).
(2) Internal glands: These are of several types
- Oil glands: In cirus cinensis (orange) the internal glands secrete a volatile oil into a central reservoir.
- Resin glands: In Pinus the resin secreting cells form one or two peripheral layers that surround a schizo- genously developed canal or duct in the leaves and stem.
- Water secreting glands: (Hydathodes water stomata) These excrete water in the form of drops (found in leaves of some herbacious angiosperms that generally grow in humid.places. Hydathodes are present at the tip of leaves of som plants e.g colocasia or along margin (Tropaeoleum). They are present at the end and veins are always open and of large size.
Hydathode have an aperture guarded b guard cells. Below the aperture is an air cavity. Below which is a loose tissue calle epithem. Epithem is made of thin walled colourless cells with intercellular spaces filled with water. Below the epithem are terminal tracheids representing the end conducting tissue.
Laticiferous tissue:
This tissue is mainly composed of thin walled elongated, branched and multinucleate tube like structures that contain colourless milky or yellow coloured juice calle latex. They are scattered throughout the ground tissue of the plant and contai stored organic matter in the form of starch, rubber, tannins, alkaloids, mucilage enzymes, protein etc. This tissue is of two types:
- Latex cells
- Latex vessels
(1) Latex cells: They differ from latex vessels in that they are not formed due to cell fusions and with other latex cells to form a network. They are branched or unbranched. They do not anastamose e.g Calotropis, Nerium, Thevetia.
(2) Latex vessels: They are composed of a large number of cells placed end to end with their transverse walls dissolved so as to form a long vessels. They are unbranched in the beginning but get branched later. Two or more latex vessels fuse with each other forming a network e.g. Papaver, Argemone, Sonchus.