NCERT Book Class 11 Biology Chapter 13 Plant Growth and Development

166 BIOLOGY

C HAPTER 13
PLANT G ROWTH AND D EVELOPMENT
13.1 Growth You have already studied the organisation of a flowering plant in Chapter
5. Have you ever thought about where and how the structures like roots,
13.2 Differentiation,
stems, leaves, flowers, fruits and seeds arise and that too in an orderly
Dedifferentiation
sequence? You are, by now, aware of the terms seed, seedling, plantlet,
and
mature plant. You have also seen that trees continue to increase in height
Redifferentiation
or girth over a period of time. However, the leaves, flowers and fruits of the
13.3 Development same tree not only have limited dimensions but also appear and fall
periodically and some time repeatedly. Why does vegetative phase precede
13.4 Plant Growth
flowering in a plant? All plant organs are made up of a variety of tissues; is
Regulators
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 13.1). 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.