Page 5 - Reproduction in Animals

How could a single cell
Though these animals lay become such a big
hundreds of eggs and release individual?
millions of sperms, all the eggs
do not get fertilised and develop Development of Embryo
into new individuals.
Fertilisation results in the formation of
This is because the eggs and
zygote which begins to develop into an
sperms get exposed to water
embryo [Fig. 6.8(a)]. The zygote divides
movement, wind and rainfall.
repeatedly to give rise to a ball of cells
Also, there are other animals in
[Fig. 6.8(b)]. The cells then begin to form
the pond which may feed
groups that develop into different tissues
on eggs. Thus, production and organs of the body. This developing
of large number of eggs and
structure is termed an embryo. The
sperms is necessary to embryo gets embedded in the wall of the
ensure fertilisation
uterus for further development
of at least [Fig. 6.8(c)].
a few of them. The embryo continues to develop in
the uterus. It gradually develops body

Uterus

Ovary
Zygote

(b)
Embedding
embryo
Uterus
Ovulation wall

(a)

Developing
embryo
(c)
Fig. 6.8 : (a) Zygote formation and development of an embryo from the zygote; (b) Ball of cells
(enlarged); (c) Embedding of the embryo in the uterus (enlarged)
70 SCIENCE

Rationalised-2023-24