The document will help you understand and revise the chapter PLANT GROWTH AND DEVELOPMENT in less time covering all the key points . it helps you to write long and short ans question in your exams of class 11th as well as build a foundation for the most competitive exam NEET
PLANT GROWTH AND DEVELOPMENT
Plant growth hormones are the intercellular mechanisms to regulate the metabolic activity occurring inside
the plant body
-The vegetative phase precedes the reproductive phase in the plants
Development is the cumulative effect of two processes growth and differentiation.
Growth:
o Growth is termed as one of the conspicuous characteristics of the living being because it is clearly
visible from outside
o Growth is irreversible permanent increase
o Growth is accompanied by both anabolic and catabolic at the expense of energy, not only anabolic
changes lead to growth but catabolic reactions will also lead to the increase of cytoplasm
o Growth at a cellular level is accompanied by the increase in the contents of protoplasm
Examples:
o Increase in the cytoplasmic content could be measured by increase in cell number, cell size, (could be
in terms of area, volume, length), increase in fresh weight or dry weight
o The expansion of leaf due to the turgidity of the guard cell could also be regarded as example of
growth
o The growth of pollen tube through the tissues of style is also regarded as growth in terms of its length
o An increase in the surface area of the dorsiventral leaf could also be termed as one of the parameters
of growth
Phases of growth
Elongation Maturation
Meristmatic
• region consists of • the region promixal to the • away from the apex but
constantly dividing cells ( merismatic zone is the proximal to the phase of
root and shoot apex) zone of elongation elongation is the phase of
• rich in protoplasm , • increased vaculation , cell maturation
possess large conspicuous largement takes place • the cells of this phase
nuclei , cell wall are therefore this region attains maximal size in
primary in nature contributes to the increase terms of wall thickening
• the cell wall is thin and in the length of the plant and protoplasmic
have abudant • cell wall deposition also modification
plasmodesmatal takes place in this region
connections creating secondary walls
Growth rates –
It could be defined as the increase in the growth per unit time . different organism have their
different ways of growth . in unicellular organism the growth is synonymous with reproduction.
, • in this type of growth curve , only one daughter cell continues to
divide And other differentiate and mature .
• this occurs when resources are limited
Arithmetic growth rate • the equation is of linear curve
• L = l +rt
• where L length at a particular time , l is initial length , r is growth rate
• for ex - root elongating at the constant rate .
• in this type of growth curve , there are lag , log and stationary phase
• lag phase represents the phase of adaptation
• log represents the phase of growth
• and stationery phase is the phase when the carrying capactivy is
reached and no growth is possible after that
Geometrical growth • occurs when resources are unlimited
rate • the equation is of exponential curve
• W=wert
• W - final size , w - intial size , r- growth rate , e - base of natural log
(2.71)
• for ex - inital phases of growth of embryo( cleavage)
Processes
DIFFERENTIATION DEDIFFERENTIATION REDIFFERENTATION
• The cells of root and • the differentiated cells • the secondary
shoot apical sometimes lose the meristems after
meristems and differentiation and replacing the
cambium differentiate gain the capacity to damaged epidermal
and mature to divide , this process is cells regain the
perform specific termed as the function and lose the
functions this process dedifferentiation ability to divide , this
of maturation is called • tumours are example process is called
differentiation. of this process redifferentiation .
• cells have to undergo • formation of • for ex - cork,
few structural changes interfasicular and cork secondary cortex ,
to take over a cambiums-, the secondary xylem
particular function differentiated
• for ex - to form parenchymatous cells
tracheary elements lose the function and
the cells would have started to divide
to lose the protoplasm again.
Development
It is a term used to refer to all the processes an organism goes through its life cycle
from germination of seed to senescence.
Plasticity-It is developmental process by which plants follows different pathways
in response to environmental or phases of life to form different kind of structures
o For ex – in cotton , coriander and larkspur , the leaves of the juvenile plant is
different from that of mature plant represents different developmental
process due to various phases of life
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