Page 99 - Science Class 08

As the eggs are laid, the male deposites sperms
over them. These sperms swim randomly in
water with the help of their long tails. When
the sperms come in contact with the eggs,
fer lisa on takes place. And, hence hundreds
of new frogs come into existence.
Internal Fer lisa on
Fer lisa on which takes place inside the body
of female is called internal fer lisa on.
Internal fer lisa on occurs in many animals
including humans, ca le, dogs, hens, etc.
Process of Internal Fer lisa on
Male sperm is ejected inside the body of the
female partner through the reproduc ve
organ.
The sperm reaches the female reproduc ve
organ where both the male gamete (sperm)
and the female gamete (egg or ovum) fuse
together and a new cell is formed called
zygote.
This zygote over a period of me changes in
emryo. This emryo develops into a new
individual.
In animals, when the fer lisa on is internal,
there are different ways in which the fer lised
egg develops into a new organism.
For example, Birds lay fer lised eggs and keep
the eggs warm by si ng on them. New young
ones hatched out of the eggs in due course of
me. Like birds, snakes and crocodiles also lay
fer lised eggs which develop into young ones.
Unlike birds and rep les, cows, dogs and
humans give birth to fully-formed young ones.
In these organisms, the fer lised egg gradually
develops into a mature body in the mother’s
womb. It comes out of the womb as a fully-
developed young one.
Science-8
Unlike other fishes, whales do not lay eggs.
Egg is an example of a single cell.
REPRODUCTION IN HUMANS
In human reproduc on system, both male and
female parents are involved. Each parent has a
different reproduc ve system. Besides, fer li-
sa on and development of the zygote takes
place inside the body of the female.
Let us study about the male reproduc ve system
and female reproduc ve system separately:
The Male Reproduc ve System
The male reproduc ve organs include a pair of
testes (singular, tes s) which are located
outside the abdominal cavity in a sac called the
scrotal sac. The testes produce millions of
sperms. The sperms leave each tes s through a
sperm duct or vas deferens. Each sperm has a
head, a middle piece and a tail. It looks very
small and it is a single cell with all the usual cell
components.
Vas deferens
Urethra
Testis
Penis Scrotal
sac
Male Reproductive Organ
When the sperms move through sperm ducts,
three different glands secrete fluids which mix
with the sperm to form semen. The semen
(sperms) now, reach the urethra which lies
inside the penis. The penis is the organ that
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