Page 126 - NCERT Science Class 10 English Medium

The swollen bottom part is the ovary, middle elongated part is the style
and the terminal part which may be sticky is the stigma. The ovary
contains ovules and each ovule has an egg cell. The male germ-cell
produced by pollen grain fuses with the female gamete present in
the ovule. This fusion of the germ-cells or fertilisation gives us the
zygote which is capable of growing into a new plant.
Thus the pollen needs to be transferred from the stamen to the
stigma. If this transfer of pollen occurs in the same flower, it is
referred to as self-pollination. On the other hand, if the pollen is
transferred from one flower to another, it is known as cross-
pollination. This transfer of pollen from one flower to another is
achieved by agents like wind, water or animals.
After the pollen lands on a suitable stigma, it has to reach the
female germ-cells which are in the ovary. For this, a tube grows
out of the pollen grain and travels through the style to reach the
ovary.
After fertilisation, the zygote divides several times to form an
embryo within the ovule. The ovule develops a tough coat and is
gradually converted into a seed. The ovary grows rapidly and ripens
to form a fruit. Meanwhile, the petals, sepals, stamens, style and
stigma may shrivel and fall off. Have you ever observed any flower
Figure
Figure 7.8
7.8
Figure
Figure 7.87.8
part still persisting in the fruit? Try and work out the advantages Figure 7.8
of seed-formation for the plant. The seed contains the future plant Germination of pollen on
stigma
or embryo which develops into a seedling under appropriate
conditions. This process is known as germination.
Activity
Activity 7.7
Activity 7.7
Activity 7.77.7
Activity
7.7
n Soak a few seeds of Bengal gram (chana)
and keep them overnight.
n Drain the excess water and cover the seeds
with a wet cloth and leave them for a day. Figure 7.97.9
Figure
Figure 7.9
Figure
7.9
Figure 7.9
Make sure that the seeds do not become dry. Germination
n Cut open the seeds carefully and observe
the different parts.
n Compare your observations with the Fig. 7.9
and see if you can identify all the parts.
7.3.3 Reproduction in Human Beings
So far, we have been discussing the variety of modes that different species
use for reproduction. Let us now look at the species that we are most
interested in, namely, humans. Humans use a sexual mode of
reproduction. How does this process work?
Let us begin at an apparently unrelated point. All of us know that
our bodies change as we become older. You have learnt changes that
take place in your body earlier in Class VIII also. We notice that our
height has increased continuously from early age till now. We acquire
teeth, we even lose the old, so-called milk teeth and acquire new ones.

How do Organisms Reproduce? 121

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