Plant Growth & Development Class 11 Notes Biology Chapter 15

 Page 1


Points To Remember
Seed Germination : The seed germinates only when favourable conditions 
for growth exists in the environment. In absence of favourable conditions it goes 
into a period of suspended growth or rest, called dormancy.
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. Some, seeds undergo a period of dormancy and can 
germinate only after dormancy period gets over.
Phytochrome : A pigment, found in plants which control the light dependent 
developmental process.
Phytohormone : Chemicals’ secreted by plants in minute quantities which 
influence the physiological activities.
Sensecene : 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, volume and weight of 
an organ or its parts or even of an individual.
Quiescence : Non germination of a viable seed due to non-availability of 
proper environmental conditions.
Vivipary : It is the germination of seed while it is still attached to the parent 
plant and is nourished by it. e.g., Rhizophora and Sonneratia. As the germinating 
seed forms a seedling. It all down into the mud due to increase in weights. In the 
mud, lateral roots develops for anchorage.
Heterophylly :Occurrence of more than one type of leaves in plants e.g., 
larkspur, Coriander leaves of Juvenile plant are different in shape from mature 
plant.
Page 2


Points To Remember
Seed Germination : The seed germinates only when favourable conditions 
for growth exists in the environment. In absence of favourable conditions it goes 
into a period of suspended growth or rest, called dormancy.
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. Some, seeds undergo a period of dormancy and can 
germinate only after dormancy period gets over.
Phytochrome : A pigment, found in plants which control the light dependent 
developmental process.
Phytohormone : Chemicals’ secreted by plants in minute quantities which 
influence the physiological activities.
Sensecene : 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, volume and weight of 
an organ or its parts or even of an individual.
Quiescence : Non germination of a viable seed due to non-availability of 
proper environmental conditions.
Vivipary : It is the germination of seed while it is still attached to the parent 
plant and is nourished by it. e.g., Rhizophora and Sonneratia. As the germinating 
seed forms a seedling. It all down into the mud due to increase in weights. In the 
mud, lateral roots develops for anchorage.
Heterophylly :Occurrence of more than one type of leaves in plants e.g., 
larkspur, Coriander leaves of Juvenile plant are different in shape from mature 
plant.
Bolting : Elongation of internodes prior to flowering in plants like Cabba ge.
Photoperiodism : Response of Plants to relative periods of day/night to 
induce flowering.
According to duration of exposure of plants to light, plants are divided in 
3 categories :
1. Long Day Plants (LDP)—Plants which need exposure to light for period
exceeding critical duration e.g., wheat, rice, cucumber.
2. Short Day Plants (SDP)—Plants that need exposure to light for period less
than the critical length e.g., Cabbage.
3. Day Neutral Plants (DNP)—There is no correlation between exposure to
light duration & induction of flowering e.g., Tomato.
Abbreviations
IAA Indole acetic acid
NAA Napththalene acetic acid
ABA Abscisic acid
IBA Indole-3 butyric acid
2.4D 2.4 dichlorophenoxy acetic acid
PGR Plant growth regulator
              Seed Dormancy Quiescence
It is the  condition of  seed when it is  The condition of a seed when it is
unable  to  germinate  in  spite  of the unable to  germinate  because the
availability of all environmental condi- conditions for germination are not
tions suitable for germination.  available.
Measurement of growth : Plant growth can be measured by a variety of 
ft 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, meristematic, elongation and maturation.
(i) Meristematic zone : New cell produced by mitotic 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.
Page 3


Points To Remember
Seed Germination : The seed germinates only when favourable conditions 
for growth exists in the environment. In absence of favourable conditions it goes 
into a period of suspended growth or rest, called dormancy.
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. Some, seeds undergo a period of dormancy and can 
germinate only after dormancy period gets over.
Phytochrome : A pigment, found in plants which control the light dependent 
developmental process.
Phytohormone : Chemicals’ secreted by plants in minute quantities which 
influence the physiological activities.
Sensecene : 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, volume and weight of 
an organ or its parts or even of an individual.
Quiescence : Non germination of a viable seed due to non-availability of 
proper environmental conditions.
Vivipary : It is the germination of seed while it is still attached to the parent 
plant and is nourished by it. e.g., Rhizophora and Sonneratia. As the germinating 
seed forms a seedling. It all down into the mud due to increase in weights. In the 
mud, lateral roots develops for anchorage.
Heterophylly :Occurrence of more than one type of leaves in plants e.g., 
larkspur, Coriander leaves of Juvenile plant are different in shape from mature 
plant.
Bolting : Elongation of internodes prior to flowering in plants like Cabba ge.
Photoperiodism : Response of Plants to relative periods of day/night to 
induce flowering.
According to duration of exposure of plants to light, plants are divided in 
3 categories :
1. Long Day Plants (LDP)—Plants which need exposure to light for period
exceeding critical duration e.g., wheat, rice, cucumber.
2. Short Day Plants (SDP)—Plants that need exposure to light for period less
than the critical length e.g., Cabbage.
3. Day Neutral Plants (DNP)—There is no correlation between exposure to
light duration & induction of flowering e.g., Tomato.
Abbreviations
IAA Indole acetic acid
NAA Napththalene acetic acid
ABA Abscisic acid
IBA Indole-3 butyric acid
2.4D 2.4 dichlorophenoxy acetic acid
PGR Plant growth regulator
              Seed Dormancy Quiescence
It is the  condition of  seed when it is  The condition of a seed when it is
unable  to  germinate  in  spite  of the unable to  germinate  because the
availability of all environmental condi- conditions for germination are not
tions suitable for germination.  available.
Measurement of growth : Plant growth can be measured by a variety of 
ft 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, meristematic, elongation and maturation.
(i) Meristematic zone : New cell produced by mitotic 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.
           Growth Mathematical expression     Curve
In Arithmetic growth : L
1
 = L
0
 + rt Linear curve
Only one daughter cell continues L
1
 = Length at  time t 
to divide mitotically while other L
0
 = Length at time zero
differentiate and matures. r = growth rate
Sigmoid Growth Curve
  Geometrical growth     Formula Shape of curve
The initial growth is W
1
 = W
0
e
rt
 Sigmoid or
slow (lag phase) and increase W
0
 = Initial size S-curve 
rapidly there-after at an W
1
 = Final Size
exponential rate (log phase) r = growth rate
In both, the progeny cells divide t = time of growth 
mitotically and continue to do so. e = base of natural
However, with limited nutrient       logarithms
supply, the growth slow down 
leading to stationary phase.
Page 4


Points To Remember
Seed Germination : The seed germinates only when favourable conditions 
for growth exists in the environment. In absence of favourable conditions it goes 
into a period of suspended growth or rest, called dormancy.
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. Some, seeds undergo a period of dormancy and can 
germinate only after dormancy period gets over.
Phytochrome : A pigment, found in plants which control the light dependent 
developmental process.
Phytohormone : Chemicals’ secreted by plants in minute quantities which 
influence the physiological activities.
Sensecene : 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, volume and weight of 
an organ or its parts or even of an individual.
Quiescence : Non germination of a viable seed due to non-availability of 
proper environmental conditions.
Vivipary : It is the germination of seed while it is still attached to the parent 
plant and is nourished by it. e.g., Rhizophora and Sonneratia. As the germinating 
seed forms a seedling. It all down into the mud due to increase in weights. In the 
mud, lateral roots develops for anchorage.
Heterophylly :Occurrence of more than one type of leaves in plants e.g., 
larkspur, Coriander leaves of Juvenile plant are different in shape from mature 
plant.
Bolting : Elongation of internodes prior to flowering in plants like Cabba ge.
Photoperiodism : Response of Plants to relative periods of day/night to 
induce flowering.
According to duration of exposure of plants to light, plants are divided in 
3 categories :
1. Long Day Plants (LDP)—Plants which need exposure to light for period
exceeding critical duration e.g., wheat, rice, cucumber.
2. Short Day Plants (SDP)—Plants that need exposure to light for period less
than the critical length e.g., Cabbage.
3. Day Neutral Plants (DNP)—There is no correlation between exposure to
light duration & induction of flowering e.g., Tomato.
Abbreviations
IAA Indole acetic acid
NAA Napththalene acetic acid
ABA Abscisic acid
IBA Indole-3 butyric acid
2.4D 2.4 dichlorophenoxy acetic acid
PGR Plant growth regulator
              Seed Dormancy Quiescence
It is the  condition of  seed when it is  The condition of a seed when it is
unable  to  germinate  in  spite  of the unable to  germinate  because the
availability of all environmental condi- conditions for germination are not
tions suitable for germination.  available.
Measurement of growth : Plant growth can be measured by a variety of 
ft 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, meristematic, elongation and maturation.
(i) Meristematic zone : New cell produced by mitotic 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.
           Growth Mathematical expression     Curve
In Arithmetic growth : L
1
 = L
0
 + rt Linear curve
Only one daughter cell continues L
1
 = Length at  time t 
to divide mitotically while other L
0
 = Length at time zero
differentiate and matures. r = growth rate
Sigmoid Growth Curve
  Geometrical growth     Formula Shape of curve
The initial growth is W
1
 = W
0
e
rt
 Sigmoid or
slow (lag phase) and increase W
0
 = Initial size S-curve 
rapidly there-after at an W
1
 = Final Size
exponential rate (log phase) r = growth rate
In both, the progeny cells divide t = time of growth 
mitotically and continue to do so. e = base of natural
However, with limited nutrient       logarithms
supply, the growth slow down 
leading to stationary phase.
154
Sigmoid growth curve
Lag phase—Growth is slow in initial stage.
Log phase : Period of maximum growth
Stationary phase—When the nutrients become limiting, growth slows down.
Relative Growth : The growth per unit time as percentage of initial size
RGR = × 100
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 nature to perform specific functions.
Conditions or factors influencing Growth
1. Nutrition 2. Availability of water 3. Temperature 4. Oxygen 5. Light
6. Gravity 7. Stress factors like minerals, water or temperature etc.
Phytohormone or Plant Growth-Regulator
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, cytokinis.
Growth inhibitor : Involved in growth inhibiting activities such as dormancy 
and abscission. e.g., Abscisic acid and Ethylene.
Hormones Functions
1. Auxins (Growth Promoters) 1. Apical dominance, cell elongation,
Promote flowering prevent premature 
leaf and fruit falling, initiate rooting 
in stem cutting, as weedicide, induce 
parthenocarpy.
2. Gibberellins 2. Delay senescence, speed up malting
process, increase in length of axis 
(grape stalk), increase in length of stem 
(sugarcane), bolting in beet, cabbages and 
many plants with rosette habit.
3 19 22 6
4 7 19
20
GA (C H O
eg. GA ,GA ,GA and
GA etc.
??
??
??
??
??
e.g.Indole 3-Acetic Acid
[2, 4-D and 2, 4, 5,-T etc.]
(Growth Promoters)
Page 5


Points To Remember
Seed Germination : The seed germinates only when favourable conditions 
for growth exists in the environment. In absence of favourable conditions it goes 
into a period of suspended growth or rest, called dormancy.
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. Some, seeds undergo a period of dormancy and can 
germinate only after dormancy period gets over.
Phytochrome : A pigment, found in plants which control the light dependent 
developmental process.
Phytohormone : Chemicals’ secreted by plants in minute quantities which 
influence the physiological activities.
Sensecene : 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, volume and weight of 
an organ or its parts or even of an individual.
Quiescence : Non germination of a viable seed due to non-availability of 
proper environmental conditions.
Vivipary : It is the germination of seed while it is still attached to the parent 
plant and is nourished by it. e.g., Rhizophora and Sonneratia. As the germinating 
seed forms a seedling. It all down into the mud due to increase in weights. In the 
mud, lateral roots develops for anchorage.
Heterophylly :Occurrence of more than one type of leaves in plants e.g., 
larkspur, Coriander leaves of Juvenile plant are different in shape from mature 
plant.
Bolting : Elongation of internodes prior to flowering in plants like Cabba ge.
Photoperiodism : Response of Plants to relative periods of day/night to 
induce flowering.
According to duration of exposure of plants to light, plants are divided in 
3 categories :
1. Long Day Plants (LDP)—Plants which need exposure to light for period
exceeding critical duration e.g., wheat, rice, cucumber.
2. Short Day Plants (SDP)—Plants that need exposure to light for period less
than the critical length e.g., Cabbage.
3. Day Neutral Plants (DNP)—There is no correlation between exposure to
light duration & induction of flowering e.g., Tomato.
Abbreviations
IAA Indole acetic acid
NAA Napththalene acetic acid
ABA Abscisic acid
IBA Indole-3 butyric acid
2.4D 2.4 dichlorophenoxy acetic acid
PGR Plant growth regulator
              Seed Dormancy Quiescence
It is the  condition of  seed when it is  The condition of a seed when it is
unable  to  germinate  in  spite  of the unable to  germinate  because the
availability of all environmental condi- conditions for germination are not
tions suitable for germination.  available.
Measurement of growth : Plant growth can be measured by a variety of 
ft 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, meristematic, elongation and maturation.
(i) Meristematic zone : New cell produced by mitotic 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.
           Growth Mathematical expression     Curve
In Arithmetic growth : L
1
 = L
0
 + rt Linear curve
Only one daughter cell continues L
1
 = Length at  time t 
to divide mitotically while other L
0
 = Length at time zero
differentiate and matures. r = growth rate
Sigmoid Growth Curve
  Geometrical growth     Formula Shape of curve
The initial growth is W
1
 = W
0
e
rt
 Sigmoid or
slow (lag phase) and increase W
0
 = Initial size S-curve 
rapidly there-after at an W
1
 = Final Size
exponential rate (log phase) r = growth rate
In both, the progeny cells divide t = time of growth 
mitotically and continue to do so. e = base of natural
However, with limited nutrient       logarithms
supply, the growth slow down 
leading to stationary phase.
154
Sigmoid growth curve
Lag phase—Growth is slow in initial stage.
Log phase : Period of maximum growth
Stationary phase—When the nutrients become limiting, growth slows down.
Relative Growth : The growth per unit time as percentage of initial size
RGR = × 100
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 nature to perform specific functions.
Conditions or factors influencing Growth
1. Nutrition 2. Availability of water 3. Temperature 4. Oxygen 5. Light
6. Gravity 7. Stress factors like minerals, water or temperature etc.
Phytohormone or Plant Growth-Regulator
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, cytokinis.
Growth inhibitor : Involved in growth inhibiting activities such as dormancy 
and abscission. e.g., Abscisic acid and Ethylene.
Hormones Functions
1. Auxins (Growth Promoters) 1. Apical dominance, cell elongation,
Promote flowering prevent premature 
leaf and fruit falling, initiate rooting 
in stem cutting, as weedicide, induce 
parthenocarpy.
2. Gibberellins 2. Delay senescence, speed up malting
process, increase in length of axis 
(grape stalk), increase in length of stem 
(sugarcane), bolting in beet, cabbages and 
many plants with rosette habit.
3 19 22 6
4 7 19
20
GA (C H O
eg. GA ,GA ,GA and
GA etc.
??
??
??
??
??
e.g.Indole 3-Acetic Acid
[2, 4-D and 2, 4, 5,-T etc.]
(Growth Promoters)
3. Cytokinins (Growth Promoters) 3. Promote cell division, induce cell
enlargement, reduce apical dominance, 
induce growth in auxiliary bud, chlorophyll 
preservation, lateral shoot growth, 
adventitious root formation.
4. [Ethylene (H
2
C = CH) 4. Promotes senescence and abscission of
leaf and fruits, promotes ripening of fruits, 
break seed and bud domancy, initiate 
germination in peanut, sprouting of potato 
tuber, promotes root growth and root hair 
formation.
 5. Inhibit seed germination, stimulate closer
of stomata, increase tolerance to various 
stress, induce dormancy in seed and bud, 
promotes ageing of leaf (senescence).
Can delay the ripening of stored fruits as 
it absorbs the ethylene.
Zeatin (trans6-purine
DMAA-Dimethylalyl
adenineand Isopentyl
adenine(IP)etc.
??
??
??
??
??
??
5. Abscisic acid (ABA)
eg. (Abscisin II Dormin)
A goreous PGR which acts
as Growth Promoters as well
growth inhibitor (mainly as
growth inhibitor)
e.g.