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BIOLOGY
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SHAHINA AKTHERGRADE 11
GULF ASIAN ENGLISH SCHOOL
ANATOMY OF FLOWERING PLANTS
Anatomy
Study of internal organisation of living organisms
Histology
Study of tissues & tissue system in multicellular organisms
1. TISSUE
• Group of cells, having common origin
Tissues
Meristematic Tissue
Permanent Tissues
Simple Permanent Tissues1) Parenchyma2) Collenchyma3) Sclerenchyma
Complex Permanent Tissues1) Xylem2) Phloem
2. MERISTEMATIC TISSUES
• Cells have power of division• A. Characteristics of Meristematic Tissues Cells are thin walled Have abundant cytoplasm Retain power of division No intracellular spaces
B. Classification of meristems :
• Based on position in plant body• (i) Apical meristems• Occur at apices• Differentiate into primary tissues• Cause increase in length• Axillary buds are present in axils of leaves
(ii) Lateral meristems :
Arranged parallel to the sides of organs of plant
Cells produced by them differentiate into secondary tissues
Cause increase in width of plant organ
e.g., Fascicular cambium & cork cambium
(iii) Intercalary meristems :
Meristems occur in between mature/permanenet tissues
Produce cells that form primary tissues
Cause increase in length
Occur at bases of internodes & leaf sheaths of grasses & other monocots;They regenerate parts removed by grazing animals
Based on origin
(i) Promeristems :
Group of meristematic cells in embryo / seedlings
Give rise to primary meristems
(ii) Primary meristems :
Formed from promeristems
Cells produced by them differentiate into primary / secondary permanent tissues
e.g., Apical meristems, fascicular cambium & intercalary meristem
(iii) Secondary meristems :
Formed at a later stage in the life of plant from permanent tissues by process of dedifferentiation, e.g., Cork cambium & inter-fascicular cambium
3. PERMANENT TISSUES
• Cells have lost power of division & become structurally & functionally specialised
Characteristics :
Cells have lost power of division
Undergone differentiation into specific types for a particular function
2 types:
(i) Simple permanent tissues ( Tissue composed of 1 type of cell)(ii) Complex permanent tissues ( Tissue is composed of more than 1
type of cell)
B. Simple Permanent Tissues :(i) Parenchyma
Cells are thin- walled
Isodiametric
Retain capacity to divide at maturity
No intracellular spaces
Main function is storage
When parenchyma cells contain a number of chloroplasts they are called chlorenchyma & when they are arranged with regular system of intercellular air spaces, they constitute aerenchyma
Forms major component of any organ of plant
(ii) Collenchyma
Cells living at maturity
Cells are variously shaped
Cell wall is unevenly thickened
Occurs below epidermis of dicot stem
Cells may possess chloroplast
Provides strength & flexibility to growing organs
(iii) Sclerenchyma Cells are dead at maturity
Cell wall is lignified evenly
Gives mechanical support to organs
Has 2 types of cells :
(a) SCLEREIDS (STONE CELLS) :
Oval/spherical & have very thick walls with narrow lumen
Occur in shells of nuts & in pulp of fruits & in tea leaves
(b) FIBRES :
Elongated & thick walled cells
Generally occur in groups
Present in xylem , phloem & cortex & pericycle
C. Complex Permanent Tissues :(i) XYLEM :
Forms continuous channel
Concerned with transport of water & minerals
Provides mechanical support
Composed of tracheary elements, xylem parenchyma & xylem fibres
(a) XYLEM VESSELS :
Long cylindrical tubular structures formed by many cells
End walls of vessel members have either single large opening / perforation / several small openings
Have thick lignified walls
Vessles are dead at maturity & found in angiosperms only
(b) XYLEM TRACHEIDS :
Elongated cells
Overlap one another at their slanting ends
Do not have perforation plates
Have thick lignified walls
Dead at maturity
(c) XYLEM PARENCHYMA ;
Thick/ thin walls of cellulose Only living components of xylem
Involved in short distance transport
Help in storage of sugars, starch, lipids & tannins
(d) XYLEM FIBRES ( SCLERENCHYMA)Dead elements
Provide mechanical support
Xylem formed in primary plant body by procambium is called primary xylem
1st formed primary xylem is called protoxylem
Later formed is called metaxylem
In stems, protoxylem lies towards pith & metaxylem towards periphery ; such an arrangement is called endarch
In roots, protoxylem lies towards periphery & metaxylem towards pith ; such an arrangement is called exarch
Xylem constituents formed by fascicular cambium constitue secondary xylem
(ii) PHLOEM
• Concerned with transport of organic substances
• Composed of sieve elements, companion cells, phloem parenchyma & phloem fibres
(a) SIEVE TUBES:
Formed by elongated sieve tube members
Cross walls have number of perforations
Mature sieve tube has peripheral cytoplasm
Functions are controlled by nucleus of companion cells
Members are characteristically present in angiosperms
(a) SIEVE CELLS :
Sieve areas are found to occur throughout the end walls & lateral walls
Cells are living, but lack nucleus
Found in lower vascular plants
(c) COMPANION CELLS:
Found in association with sieve tube members
Sieve tube elements & companion cells are connected by pit fields
Help in maintaining the pressure gradient
(d) PHLOEM PARENCHYMA :
Cells are elongated & cylindrical
Have dense cytoplasm & prominent nucleus
Stores food materials & other substances
Absent in monocot plants
(e) PHLOEM FIBRES (BAST FIBRES) :
Found along with other elements of phloem
Elongated & thick walled cells
Dead at maturity
Absent in primary phloem
1st formed primary phloem is known as protophloem
Later formed is known as metaphloem
Elements formed by fascicular cambium constitute secondary phloem
TISSUE SYSTEM IN PLANTS
• 3 tissue sysytems: (i) Epidermal tissue system (ii) Vascular tissue system (iii) Ground/ fundamental tissue system
(i) EPIDERMAL TISSUE SYSTEM• Forms outermost covering of plant body• Consists of epidermal cells, epidermal appendages &
stomata• Epidermis is outermost layer• Epidermis is single-layered• Each cell has small amount of cytoplasm & large
vacuole• Outer surface is covered with thick layer• Cuticle prevents loss of water from aerial part of plants• Epidermis is interrupted by small pores called stomata• Stoma is surrounded by 2 guard cells
• Guard cells are bean-shaped in dicot plants & dumb bell in monocots
• Outer wall is thin & inner wall is thick• They possess chloroplasts & carry out photosynthesis• Epidermal cells in their vicinity become specialised in their size
& shape• Stomatal apparatus – stomatal aperture, guard cells &
surrounding epidermal cells• Epidermis also bears appendages• Root hairs are unicellular elongation of epidermal cells of the
root• Appendages on stem epidermis are called trichomes• Help in preventing water loss by transpiration • Glandular/ secretory in many plants
(ii)VASCULAR TISSUE SYSTEM
• Includes xylem & phloem• They occur as discrete strands called vascular
bundles• Occur along same radius, vascular bundle is
called collateral• When strip of cambium is present b/w xylem &
phloem – open vascular bundle• No cambium in vascular bundle – closed
vascular bundle
• 2 phloem poles occur in a vascular bundle , separated from central xylem – bicollateral vascular bundle
• Xylem & phloem occur along different radii, alternating with each other – radial bundle
• When protoxylem is towards periphery & metaxylem is towards centre – exarch
• When protoxylem is towards centre & metaxylem is towards periphery - endarch
(iii) GROUND TISSUE SYSTEM
• Ground tissue – all tissues except epidermis & vascular bundles
• Consists of simple permanent tissues• Parenchyma cells present in cortex, pericycle;
pith & medullary rays• Ground tissue in leaves - mesophyll
My special thanx goes to my biology teacher Mrs Alermelu Natchair who gave and confirmed this permission and encouraged me to go ahead.