Exam (elaborations)
CHAPTER-15 PLANT GROWTH AND DEVELOPMENT
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CHAPTER-15 PLANT GROWTH AND DEVELOPMENT
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CBSE Quick Revision Notes (Class-11 Biology)CHAPTER-15 PLANT GROWTH AND DEVELOPMENT
• Root, stem leaves, flower, fruits and seeds arise in orderly manner in plants. The sequence of
growth is as follows-
• Plants complete their vegetative phase to move into
reproductive phase in which flower and fruits are formed
for continuations of life cycle of plant.
• Development is the sum of two processes growth and
differentiation. Intrinsic and extrinsic factors control the
process of growth and development in plants.
Growth is a permanent or irreversible increase in dry weight,
size, mass or volume of cell, organ or organism. It is
internal or intrinsic in living beings.
• In plants growth is accomplished by cell division, increase in cell number and cell
enlargement. So, growth is a quantitative phenomenon which can be measured in relation to
time.
• Plant growth is generally indeterminate due to capacity of unlimited growth throughout
the life. Meristem tissues present at the certain locality of plant body.
• The plant growth in which new cells are always being added to plant body is due to meristem
is called open form of growth.
• Root apical meristem and shoot apical meristem are responsible for primary growth and
elongation of plant body along the axis.
• Intercalary meristem located at nodes produce buds and new
branches in plants.
• Secondary growth in plants is the function of lateral meristem that
is vascular cambium and cork cambium.
Growth is measurable
At cellular level, growth is the increase in amount of protoplasm. It
is difficult to measure the increase in amount of protoplasm but
increase in cell, cell number and cell size can be measured.
The parameter used to measure growth is increase in fresh weight,
dry weight, length, area, and volume and cell number. All
parameters are not used for every kinds of growth.
Phases of
growth
Formative Phase Phase of Enlargement Phase of Maturation
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, Formative phase is also called as the phase of cell formation or cell division. It occurs at root
apex, shot apex and other region having meristematic tissue. The rate of respiration is very
high in the cells undergoing mitosis division in formative phase.
Phase of Enlargement- newly formed cells produced in formative phase undergo
enlargement. Enlarging cells also develops vacuoles that further increase the volume of cell.
Cell enlargement occurs in all direction with maximum elongation in conducting tissues and
fibres.
Phase of maturation- the enlarged cells develops into special
or particular type of cells by undergoing structural and
physiological differentiation.
Growth Rate- increase in growth per unit time is called growth
rate. Growth rate may be arithmetic or geometrical.
Arithmetic Growth- the rate of growth is constant and increase in
growth occurs in arithmetic progression- 2,4,6,8 ……. It is
found in root and shot elongation.
Lt = L0 + rt
Length after time = length at beginning + growth rate x time.
Geometric Growth- here initial growth is slow and increase rapidly thereafter. Every cell
divides. The daughter cells grow and divide and the granddaughter cells that result into
exponential growth.
Geometrical growth is common in unicellular oranisms when grows in nutrient rich medium.
Sigmoid growth curve consists of fast dividing exponential phase and stationary phase. It is
typical of most living organisms in their natural environment.
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