Plant tissues
Short answer type questions
Q1. Give an example of secondary mesristem.
Ans. Vascular cambium of dicot root.
Q2. What makes the root's apical meristem sub-terminal?
Ans. Presence of root cap makes the root's apical meristem sub-terminal.
Q3. What type of tissue constitutes calyptrogen?
Ans. Metistematic tissues.
Q4. List the parts of periderm.
Ans. Phellogen(cork cambium), phelloderm(secondary cortex) and phellum(cork).
Q5. What does fascicular cambium give rise to?
Ans. Secondary vascular tissues.
Q6. What is most significant role of peticycle?
Ans. The formation of lateral roots and helps in secondary growth.
Q7. What is the most significant role of fusiform initials?
Ans. Differentiate into secondary xylem and pholem.
Q8. Mention the most significant role of bulliform cells.
Ans. To reduce transpiration by rolling of the leaf during dry seasons.
Q9. What is a bicollateral vascular bundle?
Ans. A vascular bundle having both external and internal phloem is called bicollateral vascular bundle.
Q10. What is the function of root hairs?
Ans. Absorb water and mineral nutrients from the soil.
Q11. Why is propagation through grafting not successful in monocots?
Ans. In monocots, vascular bundles are scattered, and moreover secondary growth is wanting due to the absence of cambium the union of xylem and phloem is in grafting is not possible. Hence propagation through grafting is not successful in monocots.
Q12. Where is the quiescent centre located?
Ans. Its located in the root apex.
Q13. What is dendrochronology?
Ans. Its is the determination of age of tree by counting the annual rings.
Q14. Which group of plants contains collateral, conjoint and open vascular bundles?
Ans. Dicotyledonous stems.
Q15. What kind of vascular bundies are found in monocotyledonous plants?
Ans. The vascular bundles are scattered, collateral and closed.
Q16. Mention one significant difference between the following:
i) Vascular cambium and cork cambium
ii) Trachieds and vessels
iii) Open vascular bundle and closed vascular bundle
iv) Phellem and Phelloderm
v) Exarch xylem and Endarch xylem
vi) Heartwood and sap wood
vii) Root apex and shoot apex
Ans. i) Vascular cambium Cork cambium
It develops between It develops from cortex or
Primary and secon- pericycle and gives rise to
dary phloem, and periderm.
gives rise to secon-
dary vascular
tissue.
These are single- These are made up of a
celled, elongated row cells, cylindrical
structures with tubes with wide ends,
tapering ends, and longer in size.
and shorter in size.
iii) Open vascular Closed vascular
Bundles bundles
These vascular bun- These vascular bundle
dle conataining do not contain cambium
cambium, in between in between xylem and
xylem and phloem. phloem. E.g.monocot
E.g. dicot stem. stem.
iv) Phellem Phelloderm
Dead tissue formed Living parenchymatous
by the activity of cork tissue formed by the
cambium in the outer activity of cork
region of cortex during cambium in the inner
secondary growth. side of cortex during
secondary growth.
v) Exarch Xylem Endarch Xylem
The protoxylem The protoxylem lies
lies towards the toward the centre.
periphery. E.g.stems.
E.g. roots.
vi) Sap wood Heart wood
The outer light The inner dark coloured
coloured region of region of wood is known
wood is known as as heart wood. It consists
sapwood. It consists of dead cells.
of living cells.
vii) Root apex Shoot apex
Protected by root cap Protected by young leaves
and sub terminal in and terminal meristem
position. in the shoots.
Long Answer Type Questions
Q1. Give an account of the various types of
vascular bundles in plants.
Ans. There are mainly three types of vascular bundles on the basis of relative
position of xylem and phloem. They are:
i) Radial: The xylem and the phloem are arranged alternatively on different radii e.g. roots.
ii) Conjoint: The xylem and phloem together form a bundle. There are two subtype:
a) Collateral: This xylem and phloem combine together and lie on the same radius. In such an arrangement, xylem occupies the internal position and pholem occupies the external position. These bundles maybe open (when cambium is present example- Dicot stem) or closed (when cambium is absent example -monocot stem)
b) Bicollateral:The phloem and cambium lie on both side of the xylem. Simultaneously, two cambium strips also occur. The sequence of arrangement of tissues is outer phloem, outer cambium ,xylem, inner cambium, inner phloem .example -stem of solanaceae and curcurbitaceae.
iii) Concentric: The xylem and phloem lie concentrically, that is, one surrounds the other. When xylem is in the centre-amphicribal e.g.Ferns.When phloem is in the centre-amphivasal. E.g. Dracaena and yucca.
Q2. Write the main characteristics of a meristematic tissue (Meristems).
Ans. The main characteristics of a meristematic tissue are:
1. The cells of meristematic tissues are thin walled,mostly isodiametric and are compactly arranged without any intercellular spaces.
2. They are large nucleus.
3. They have dense cytoplasm either with very small vacuoles or without any vacuole.
4. The cells are capable of continuous division.
5. The cells have poorly develop endoplasmic reticulum and mitochondria.
Q4. Write short notes on the following:
i) Annual ring
ii) Quiescent centre
iii) Spring wood and autumn wood
i) Annual ring: A line appearing in the cross section marking the end of growing seasons ans showing the volume of wood adding during the year is called annual ring. In other words, the formed during one growth period is termed as annual ring. The annual rings are formed in temperate regions with seasonal variations.
ii) Quiescent centre : Clowes (1956) ,discovered a central cup-like region of cells lying between the root cap and the active meristematic region. The cells in this region have a low mitotic activity and have low concentration of DNA,RNA and the protein than the other cells in the root apex. This group of cells, which appears in the shape of hemisphere, was termed as quiescent centre.
iii) Spring wood and autumn wood : The wood formed in the spring is known as spring wood and that formed in dry summer or cold winter is known as autumn wood.
Q6. Write the anatomical difference between dicot and monocot root.
Ans. Dicot Root Monocot root
1. Vascular bundles 1. Vascular bundles are
are usually 2-6. usually 6-20.
2. Conjunctive tissue 2. Connective tissue is
is parenchymatous; its mostly sclerenchymatous
cells differentiate into but sometimes parenchy
vascular cambium. matous; it never
differentiates into
vascular cambium.
3. Cambium appears as 3. Cambium is altoghter
a secondary meristem absent.
at the time of secondary
growth.
4. Pith is absent or poorly 4. Pith is large and well-
developed. developed.
5. Bundle sheath is 5. Bundle sheath is
absent. present.
Q6.What are the differentiate between a
monocot and dicot stem?
Ans. Monocot stem Dicot stem
1. Ground tissue made 1. Ground tissue differentia
up of similar cells ted into cortex, endodermis
without differentiation ,pericycle,pith.
cortex, endodermis and
pericycle.
2. Vascular bundles are 2. Vascular bundles are few
numerous and scattered and arranged in a ring.
in ground tissue.
3. Bundle sheath 3. Bundle sheath absent.
present.
4. Vascular bundles are 4. Vascular bundles are open
closed and endarch. and endarch.
5. Secondary growth 5. Secondary growth present.
absent.
6. Medually rays 6. Medually rays present.
absent.
7. Lysigenous cavity 7. Lysigenous cavity absent.
present.
8. Pith absent. 8. Pith present.
Q7. Write the difference between root and stem.
Ans. Root Stem
1. Epidermis without 1. Epidermis with cuticle.
cuticle.
2. Hairs are unicellular. 2. Hairs are multicellular.
3.Chlorenchymatous 3. Usually present in young
tissue absent. stems.
4. Endodermis is very 4. Endodermis is generally
distinct. absent.
5. Pericycle is usually 5. Pericycle is usually
single layered. multilayered.
6.Vascular bundles are 6. Vascular bundle conjoint,
radial. and collateral.
7.Xylem showing 7. Xylem showing endarch
exarch condition. condition.
Q8.What is Xylem? Explain the structure of various xylem elements.
Ans. Xylem a permanent,complex tissue concerned with the conduction of water and minerals. The main components of xylem are:
1. Trachieds: There are elongated dead cells,spindle-shaped,enclosed a large empty cavity. They appear polygonal in cross section. Thickening of their cell wall is caused by the deposition of lignin. They may be annual, scalariform and pitted. They are primarily meant for conduction of water and providing mechanical strength.
2. vessels : These are cylindrical,tube-like structures formed by a row of cells placed end to end. The transverse wall between the cell partly or completely dissolves to form a complete channel or water pipe. They also process different types of thickings of cellulose and lignin of their cell wall . They occur only in stems and roots of angiosperms and their main function is conduction of water.
3. Xylem parenchyma : They are made up of thin-walled, living parenchyma cells. Their function is storage of water and food materials.
4. Xylem fibres: They consists of long, slender, pointed, dead, sclerenchymatous cells. These fibres provide mechanical strength. They have thick lignified walls and narrow lumen.
Q9. What is Phloem? Discribe the structure of various components of Phloem.
Ans. Phloem is a specialized complex tissue mainly responsible for the translocation of food materials. Sieve elements, Companion cells, Phloem parenchyma and Phloem fibres and the basic components of phloem.
1.Sieve elements: The conducting of phloem are collectively known as sieve elements. There are two kinds of sieve elements:i) sieve cells, and ii)sieve tube elements. Sieve cells are single cells with less specialized sieve areas usually in their lateral walls. Sieve Tubes are longitudinal file of cells with highly specialized pores(known as sieve plates) usually in or near an end wall.
2. Companion cells: These are parenchyma cells associated with sieve tube elements. They are living cells having dense cytoplasm. They remain connected with the sieve tube by pores.
3. Phloem parenchyma: They are typical parenchyma cells found associated with sieve tube cells. These cells are elongated, pointed, cylindrical with storage of starch, fat and other organic food materials, accumulation of tannins, resins, crystals, mucilage, etc. And lateral transport of soluble food materials and water.
4. Phloem fibres: They are typically elongated cells with interlock ends and lignified walls having single pits. Besides providing support, phloem fibres also also play a role in the translocation of food materials. They are composed of dead cells.
Q10. What is meant by secondary growth? Which meristems are responsible for secondary growth?
Ans. The formation of secondary tissues from lateral meristem is called secondary growth. It helps in increase of birth. Secondary tissues are formed(secondary growth) from two types of lateral meristems. They are:
1. Vascular cambium :It is present between primary xylem and primary phloem and is called fascicular cambium. In the medullary region, interfascicular cambium is formed between two vascular bundles. Interfascicular and vascular cambium form the complete ring in the stem. Cambium cells divide to form secondary xylem and secondary phloem.
2. Cork cambium(phellogen) : It develops in the cortex region. The cork cambium produces the cork(phellem) tissue towards the epidermis and produces the phelloderm on the inner side. Cork cambium (phellogen), cork(phellem) and phellodetm constitute the periderm. The formation of peridetm starts with the production of secondary vascular tissues.
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