All plant cells are descendants of the zygote (fertilized egg). The zygote develops into a mature plant through growth and
differentiation forming roots, leaves, branches, flowers, fruits and seeds. Then they eventually die.
GROWTH
- Growth is an irreversible permanent increase in size of an
organ or its parts or an individual cell. Detection of zones of
- It involves metabolic processes that consume energy. elongation by the
parallel line
Plant Growth Generally is Indeterminate technique.
- Plant growth continues
Zones A, B, C, D
throughout the life due to the immediately behind
presence of meristems. the apex have
- Meristematic cells have elongated most.
capacity to divide & self-
perpetuate.
Growth Rates
- The growth where new cells
- It is the increased growth per unit time.
are always added to the plant
- The growth rate may be arithmetic or geometrical.
body by the meristem is called
Arithmetic growth:
open form of growth.
- Primary growth: It occurs - In this, following mitotic division, only one daughter cell
due to root apical meristem & continues to divide while the other differentiates & matures.
shoot apical meristem. It - On plotting the length of the organ against time, a linear
causes the elongation of the curve is obtained.
plants along the axis.
- Secondary growth (In
gymnosperms & dicots): It
occurs due to lateral meristems, vascular cambium &
cork-cambium. It causes increase in the girth of organs.
Growth is Measurable
- At cellular level, growth occurs due to increase in the
amount of protoplasm.
- Increase in protoplasm is difficult to measure directly. So
growth is measured by parameters like increase in fresh Mathematically, it is expressed as Lt = L0 + rt
weight, dry weight, length, area, volume & cell number. E.g. Lt = length at time ‘t’
o Cell number: E.g. A maize root apical meristem can L0 = length at time ‘zero’
produce more than 17,500 new cells per hour. r = growth rate / elongation per unit time.
o Cell size: E.g. Cells in a watermelon can increase in size Geometrical growth:
by up to 3,50,000 times.
- Here, both daughter cells continue mitotic cell division.
o Length: E.g. Growth of a pollen tube.
- In most systems, the initial growth is slow (lag phase),
o Surface area: E.g. Growth in a dorsi-ventral leaf.
then it increases rapidly (log or exponential phase).
Phases of Growth - If nutrient supply is limited, the growth slows down
3 phases: meristematic, elongation & maturation. leading to a stationary phase.
• Meristematic phase: It occurs in the meristems at the root - On plotting the parameter of growth against time, we get a
apex & the shoot apex. Here, cells have rich protoplasm typical sigmoid (S) curve.
and large nuclei. Cell walls are primary, thin & cellulosic - A sigmoid curve is a characteristic of living organism
with abundant plasmodesmata. growing in a natural environment. It is typical for all cells,
• Elongation phase: It occurs in cells proximal (just next, tissues and organs of a plant.
away from the tip) to the meristematic zone. The cells have
increased vacuolation, size and new cell wall deposition.
• Maturation phase: It occurs in the cells further away from
the apex, i.e., more proximal to the phase of elongation.
The cells attain maximal size in terms of wall thickening
and protoplasmic modifications.
1
, Exponential growth is
expressed as W1 = W0 ert
W1 = final size (weight,
height, number etc.)
W0 = initial size at the
beginning of period
r = growth rate (relative)
t = time of growth
e = base of natural
logarithms
Diagrammatic comparison of absolute & relative growth rates
- Here, r is relative growth rate. It is also the measure of Conditions (essential elements) for Growth
ability of plant to produce new plant material (efficiency 1. Water: Essential for cell enlargement. Turgidity of cells
index). Hence, final size W1 depends on initial size, W0. helps in extension growth. Water provides medium for
- Quantitative comparisons between the growth can also be enzymatic activities needed for growth.
made in 2 ways: 2. Oxygen: It helps to release metabolic energy for growth.
(i) Absolute growth rate: Measurement & comparison 3. Nutrients: Macro & micro elements are needed for the
of total growth per unit time. synthesis of protoplasm and act as source of energy.
(ii) Relative growth rate: Measurement of growth of the 4. Temperature: At optimum temperature, growth is
given system per unit time expressed on a common maximum. Deviation from this may harm the plants.
basis, e.g., per unit initial parameter. 5. Light & gravity: Affect certain phases/stages of growth.
DIFFERENTIATION, DEDIFFERENTIATION & REDIFFERENTIATION
- Differentiation is the process in which the cells in - The dedifferentiated cells can divide and produce cells that
meristems (root apical & shoot-apical) and cambium again lose the capacity to divide but mature to perform
differentiate and mature to perform specific functions. specific functions. It is called redifferentiation.
- In this, cell walls & protoplasm undergo major structural - Plant growth is open, i.e., it can be indeterminate or
changes. The capacity of cell division is lost. determinate. Differentiation in plants is also open, because
E.g. Loss of protoplasm to form a tracheary element. They cells/tissues arising out of the same meristem have
also develop very strong, elastic, lignocellulosic secondary different structures at maturity.
cell walls to carry water to long distances even under - Final structure at maturity of cell/tissue is also determined
extreme tension. by the location of the cell.
- Under certain conditions, living differentiated cells regain E.g. cells positioned away from root apical meristems
the capacity of division. This is called dedifferentiation. differentiate as root-cap cells, while those pushed to the
E.g. formation of meristems (interfascicular cambium & periphery mature as epidermis.
cork cambium) from differentiated parenchyma cells.
DEVELOPMENT
- It is a process that includes all changes in the life cycle of
an organism from seed germination to senescence.
- It is the sum of growth and differentiation.
- Plants follow different pathways in response to
environment or phases of life to form different kinds of
structures. This ability is called plasticity. E.g.
• Heterophylly due to phases of life: E.g. In cotton,
Factors controlling the development:
coriander and larkspur, the leaves of the juvenile plants and
• Intrinsic factors: Include intracellular (genetic) or
mature plants are different in shape.
intercellular factors (such as plant growth regulators).
• Heterophylly due to environment: E.g. Difference in
• Extrinsic factors: Include light, temperature, water,
shapes of leaves produced in air and water (e.g. buttercup).
oxygen, nutrition, etc.
2
differentiation forming roots, leaves, branches, flowers, fruits and seeds. Then they eventually die.
GROWTH
- Growth is an irreversible permanent increase in size of an
organ or its parts or an individual cell. Detection of zones of
- It involves metabolic processes that consume energy. elongation by the
parallel line
Plant Growth Generally is Indeterminate technique.
- Plant growth continues
Zones A, B, C, D
throughout the life due to the immediately behind
presence of meristems. the apex have
- Meristematic cells have elongated most.
capacity to divide & self-
perpetuate.
Growth Rates
- The growth where new cells
- It is the increased growth per unit time.
are always added to the plant
- The growth rate may be arithmetic or geometrical.
body by the meristem is called
Arithmetic growth:
open form of growth.
- Primary growth: It occurs - In this, following mitotic division, only one daughter cell
due to root apical meristem & continues to divide while the other differentiates & matures.
shoot apical meristem. It - On plotting the length of the organ against time, a linear
causes the elongation of the curve is obtained.
plants along the axis.
- Secondary growth (In
gymnosperms & dicots): It
occurs due to lateral meristems, vascular cambium &
cork-cambium. It causes increase in the girth of organs.
Growth is Measurable
- At cellular level, growth occurs due to increase in the
amount of protoplasm.
- Increase in protoplasm is difficult to measure directly. So
growth is measured by parameters like increase in fresh Mathematically, it is expressed as Lt = L0 + rt
weight, dry weight, length, area, volume & cell number. E.g. Lt = length at time ‘t’
o Cell number: E.g. A maize root apical meristem can L0 = length at time ‘zero’
produce more than 17,500 new cells per hour. r = growth rate / elongation per unit time.
o Cell size: E.g. Cells in a watermelon can increase in size Geometrical growth:
by up to 3,50,000 times.
- Here, both daughter cells continue mitotic cell division.
o Length: E.g. Growth of a pollen tube.
- In most systems, the initial growth is slow (lag phase),
o Surface area: E.g. Growth in a dorsi-ventral leaf.
then it increases rapidly (log or exponential phase).
Phases of Growth - If nutrient supply is limited, the growth slows down
3 phases: meristematic, elongation & maturation. leading to a stationary phase.
• Meristematic phase: It occurs in the meristems at the root - On plotting the parameter of growth against time, we get a
apex & the shoot apex. Here, cells have rich protoplasm typical sigmoid (S) curve.
and large nuclei. Cell walls are primary, thin & cellulosic - A sigmoid curve is a characteristic of living organism
with abundant plasmodesmata. growing in a natural environment. It is typical for all cells,
• Elongation phase: It occurs in cells proximal (just next, tissues and organs of a plant.
away from the tip) to the meristematic zone. The cells have
increased vacuolation, size and new cell wall deposition.
• Maturation phase: It occurs in the cells further away from
the apex, i.e., more proximal to the phase of elongation.
The cells attain maximal size in terms of wall thickening
and protoplasmic modifications.
1
, Exponential growth is
expressed as W1 = W0 ert
W1 = final size (weight,
height, number etc.)
W0 = initial size at the
beginning of period
r = growth rate (relative)
t = time of growth
e = base of natural
logarithms
Diagrammatic comparison of absolute & relative growth rates
- Here, r is relative growth rate. It is also the measure of Conditions (essential elements) for Growth
ability of plant to produce new plant material (efficiency 1. Water: Essential for cell enlargement. Turgidity of cells
index). Hence, final size W1 depends on initial size, W0. helps in extension growth. Water provides medium for
- Quantitative comparisons between the growth can also be enzymatic activities needed for growth.
made in 2 ways: 2. Oxygen: It helps to release metabolic energy for growth.
(i) Absolute growth rate: Measurement & comparison 3. Nutrients: Macro & micro elements are needed for the
of total growth per unit time. synthesis of protoplasm and act as source of energy.
(ii) Relative growth rate: Measurement of growth of the 4. Temperature: At optimum temperature, growth is
given system per unit time expressed on a common maximum. Deviation from this may harm the plants.
basis, e.g., per unit initial parameter. 5. Light & gravity: Affect certain phases/stages of growth.
DIFFERENTIATION, DEDIFFERENTIATION & REDIFFERENTIATION
- Differentiation is the process in which the cells in - The dedifferentiated cells can divide and produce cells that
meristems (root apical & shoot-apical) and cambium again lose the capacity to divide but mature to perform
differentiate and mature to perform specific functions. specific functions. It is called redifferentiation.
- In this, cell walls & protoplasm undergo major structural - Plant growth is open, i.e., it can be indeterminate or
changes. The capacity of cell division is lost. determinate. Differentiation in plants is also open, because
E.g. Loss of protoplasm to form a tracheary element. They cells/tissues arising out of the same meristem have
also develop very strong, elastic, lignocellulosic secondary different structures at maturity.
cell walls to carry water to long distances even under - Final structure at maturity of cell/tissue is also determined
extreme tension. by the location of the cell.
- Under certain conditions, living differentiated cells regain E.g. cells positioned away from root apical meristems
the capacity of division. This is called dedifferentiation. differentiate as root-cap cells, while those pushed to the
E.g. formation of meristems (interfascicular cambium & periphery mature as epidermis.
cork cambium) from differentiated parenchyma cells.
DEVELOPMENT
- It is a process that includes all changes in the life cycle of
an organism from seed germination to senescence.
- It is the sum of growth and differentiation.
- Plants follow different pathways in response to
environment or phases of life to form different kinds of
structures. This ability is called plasticity. E.g.
• Heterophylly due to phases of life: E.g. In cotton,
Factors controlling the development:
coriander and larkspur, the leaves of the juvenile plants and
• Intrinsic factors: Include intracellular (genetic) or
mature plants are different in shape.
intercellular factors (such as plant growth regulators).
• Heterophylly due to environment: E.g. Difference in
• Extrinsic factors: Include light, temperature, water,
shapes of leaves produced in air and water (e.g. buttercup).
oxygen, nutrition, etc.
2
