Plant Growth And Development | पादप वृद्धि एवं परिवर्धन | Class 11 biology hindi audiobook | NCERT

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Plant Growth And Development | |पादप वृद्धि एवं परिवर्धन | Class 11 biology hindi audiobook | NCERT

Have you ever thought about where and how the structures like roots,
stems, leaves, flowers, fruits and seeds arise and that too in an orderly
sequence? You are, by now, aware of the terms seed, seedling, plantlet,
mature plant. You have also seen that trees continue to increase in height
or girth over a period of time. However, the leaves, flowers and fruits of the
same tree not only have limited dimensions but also appear and fall
periodically and some time repeatedly. Why does vegetative phase precede
flowering in a plant? All plant organs are made up of a variety of tissues; is
there any relationship between the structure of a cell, a tissue, an organ
and the function they perform? Can the structure and the function of these
be altered? All cells of a plant are descendents of the zygote. The question
is, then, why and how do they have different structural and functional
attributes? Development is the sum of two processes: growth and
differentiation. To begin with, it is essential and sufficient to know that the
development of a mature plant from a zygote (fertilised egg) follow a precise
and highly ordered succession of events. During this process a complex
body organisation is formed that produces roots, leaves, branches, flowers,
fruits, and seeds, and eventually they die (Figure 15.1). The first step in the
process of plant growth is seed germination. The seed germinates when
favourable conditions for growth exist in the environment. In absence of
such favourable conditions the seeds do not germinate and goes into a
period of suspended growth or rest. Once favourable conditions return,
the seeds resume metabolic activities and growth takes place.
In this chapter, you shall also study some of the factors which
govern and control these developmental processes. These factors are both
intrinsic (internal) and extrinsic (external) to the plant
Growth is one of the most conspicuous events in any living organism. It is an irreversible increase expressed in parameters such as size, area, length, height,volume, cell number etc. It conspicuously involves increased protoplasmic material.In plants, meristems are the sites of growth. Root and shoot apical meristemssometimes alongwith intercalary meristem, contribute to the elongation growth ofplant axes. Growth is indeterminate in higher plants. Following cell division in root and shoot apical meristem cells, the growth could be arithmetic or geometrical.
Growth may not be and generally is not sustained at a high rate throughout the life of cell/tissue/organ/organism. One can define three principle phases of growth –
the lag, the log and the senescent phase. When a cell loses the capacity to divide, it leads to differentiation. Differentiation results in development of structures that is commensurate with the function the cells finally has to perform. General principles for differentiation for cell, tissues and organs are similar. A differentiated cell may dedifferentiate and then redifferentiate. Since differentiation in plants is open, the development could also be flexible, i.e., the development is the sum of growth and
differentiation. Plant exhibit plasticity in development.
Plant growth and development are under the control of both intrinsic and
extrinsic factors. Intercellular intrinsic factors are the chemical substances, called plant growth regulators (PGR). There are diverse groups of PGRs in plants, principally belonging to five groups: auxins, gibberellins, cytokinins, abscisic acid and ethylene.
These PGRs are synthesised in various parts of the plant; they control different differentiation and developmental events. Any PGR has diverse physiological effects on plants. Diverse PGRs also manifest similar effects. PGRs may act synergistically or antagonistically. Plant growth and development is also affected by light, temperature, nutrition, oxygen status, gravity and such external factors.
Flowering in some plants is induced only when exposed to certain duration of photoperiod. Depending on the nature of photoperiod requirements, the plants are called short day plants, long day plants and day-neutral plants. Certain plants also need to be exposed to low temperature so as to hasten flowering later in life.

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