Page 127 - NCERT Science Class 10 English Medium

All of these are changes that can be grouped under the general process
of growth, in which the body becomes larger. But in early teenage years,
a whole new set of changes occurs that cannot be explained simply as
body enlargement. Instead, the appearance of the body changes.
Proportions change, new features appear, and so do new sensations.
Some of these changes are common to both boys and girls. We begin
to notice thick hair growing in new parts of the body such as armpits
and the genital area between the thighs, which can also become darker
in colour. Thinner hair can also appear on legs and arms, as well as on
the face. The skin frequently becomes oily and we might begin to develop
pimples. We begin to be conscious and aware of both our own bodies
and those of others in new ways.
On the other hand, there are also changes taking place that are
different between boys and girls. In girls, breast size begins to increase,
with darkening of the skin of the nipples at the tips of the breasts. Also,
girls begin to menstruate at around this time. Boys begin to have new
thick hair growth on the face and their voices begin to crack. Further,
the penis occasionally begins to become enlarged and erect, either in
daydreams or at night.
All of these changes take place slowly, over a period of months and
years. They do not happen all at the same time in one person, nor do
they happen at an exact age. In some people, they happen early and
quickly, while in others, they can happen slowly. Also, each change does
not become complete quickly either. So, for example, thick hair on the
face in boys appears as a few scattered hairs first, and only slowly does
the growth begin to become uniform. Even so, all these changes show
differences between people. Just as we have differently shaped noses or
fingers, so also we have different patterns of hair growth, or size and
shape of breast or penis. All of these changes are aspects of the sexual
maturation of the body.
Why does the body show sexual maturation at this age? We have
talked about the need for specialised cell types in multi-cellular bodies
to carry out specialised functions. The creation of germ-cells to participate
in sexual reproduction is another specialised function, and we have seen
that plants develop special cell and tissue types to create them. Human
beings also develop special tissues for this purpose. However, while the
body of the individual organism is growing to its adult size, the resources
of the body are mainly directed at achieving this growth. While that is
happening, the maturation of the reproductive tissue is not likely to be
a major priority. Thus, as the rate of general body growth begins to slow
down, reproductive tissues begin to mature. This period during
adolescence is called puberty.
So how do all the changes that we have talked about link to the
reproductive process? We must remember that the sexual mode of
reproduction means that germ-cells from two individuals have to join
together. This can happen by the external release of germ-cells from the
bodies of individuals, as happens in flowering plants. Or it can happen
by two individuals joining their bodies together for internal transfer of
germ-cells for fusion, as happens in many animals. If animals are to

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