These notes for CBSE Class 11 Biology, Chapter 15, cover Plant Growth and Development. Key concepts explained include growth as an irreversible increase in size, and its measurement through parameters like weight and length. The three phases of growth – meristematic, elongation, and maturation – are detailed, along with growth rate, differentiation, dedifferentiation, and redifferentiation. The chapter also defines important terms like abscission, apical dominance, dormancy, photoperiodism, phytochrome, phytohormone, senescence, and vernalisation. Phytohormones are classified into growth-promoting (auxin, gibberellins, cytokinins) and growth-inhibiting (abscisic acid, ethylene) types, influencing various physiological activities. These notes are ideal for students preparing for their exams, offering a concise overview of the chapter's core topics.
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Abscission : Shedding of plant organs like leaves, flowers and fruits etc.
from the mature plant.
Apical dominance : Suppression of the growth of lateral buds in presence
of apical bud.
Dormancy : A period of suspended activity and growth usually associated
with low metabolic rate.
Photoperiodism : Response of plant to the relative length of day and night
period to induce flowering.
Phytochrome : A pigment, which control the light dependent developmental
process.
Phytohormone : Chemicals secreted by plants in minute quantities which
influence the physiological activities.
Senescene : The last phase of growth when metabolic activities decrease.
Vernalisation : A method of promoting flowering by exposing the young
plant to low temperature.
Growth : An irreversible permanent increase in size of an organ or its parts
or even of an individual.
Abbreviations
IAA Indole acetic acid
NAA Naphthalene acetic acid
ABA Abscissic acid
IBA Indole-3 butyric acid
2.4D 2.4 dichlorophenoxy acetic acid
PGR Plant growth regulator
Measurement of growth : Plant growth can be measured by a variety of
parameters like increase in fresh weight, dry weight, length, area, volume and
cell number.
Phases of growth : The period of growth is generally divided into three
phases, namely, meristamatic, elongation and maturation.
(i) Meristematic zone : New cell produced by metotic division at root-tip
and shoot tip thereby show increase in size. Cells are rich in protoplasm and
nuclei.
(ii) Elongation zone : Zone of elongation lies just behind the meristematic
zone and concerned with enlargement of cells.
(iii) Maturation zone : The portion lies proximal to the phase of elongation.
The cells of this zone attain their maximum size in terms of wall thickning and protoplasmic modification.
Growth rate : The increased growth per unit time is termed as growth rate.
The growth rate shows an increase that may be arithmetic or geometrical.
Differentiation : A biochemical or morphological change in meristemic
cell (at root apex and shoot apex) to differentiate into permanent cell is called
differentiation.
Dedifferentiation : The phenomenon of regeneration of permanent tissue
to become meristematic is called dedifferentiation.
Redifferentiation : Meristems/tissue are able to produces new cells that
once again lose the capacity to divide but mature to perform specific functions.
Growth promoting hormones : These are involved in growth promoting
activities such as cell division, cell enlargement, flowering, fruiting and seed
formation. e.g., Auxin, gibberellins, cytokinins.
Growth inhibitor : Involved in growth inhibiting activities such as dormancy
and abscission. e.g.,
Abscisic
acid and Ethylene. a
These notes define growth as an irreversible, permanent increase in the size of a plant organ or individual, and development as the sequence of changes from germination to senescence.
The three main phases of plant growth are the meristematic phase (cell division), elongation phase (cell enlargement), and maturation phase (cells attain maximum size and modify).
Phytohormones, or plant growth regulators, are chemicals produced by plants in small amounts that influence physiological activities. They are classified as growth-promoting (auxins, gibberellins, cytokinins) and growth-inhibiting (abscisic acid, ethylene).
Photoperiodism is the response of plants to the relative length of day and night, which induces flowering.
Apical dominance is the suppression of the growth of lateral buds by the presence of the apical bud.
Plant growth can be measured using parameters like increase in fresh weight, dry weight, length, area, volume, and cell number.
Differentiation is the process where meristematic cells change morphologically or biochemically to become permanent cells. Dedifferentiation is the reverse process, where permanent tissues regain their meristematic capacity.
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