Page 98 - Science Class 08

reproduc on involves in crea on of new can also say that the organisms in which male
individual through the union of reproduc ve
cells called gametes where the gametes come
from different parents.
The male gamete is called the sperm whereas
the female gamete is called the egg or ovum.
When the male gamete (sperm) and the female
gamete (ovum) fuse together a third new cell is
formed called zygote.
Sperm + Ovum Õ Zygote
Zygote
The process of fusion of the sperm and ovum is
called fer lisa on. This process is important
for every kind of sexual reproduc on.
The zygote (fer lised egg) divides many mes to
form a ball of cells. This grows into an embryo.
The embryo changes over a period of me to
form the new organism.
BISEXUAL AND UNISEXUAL ORGANISMS
There are certain mul cellular organisms in
which the male and female sex organs are
present in the same individual. In this organisms,
male sex organs produce male gamete and
female gametes. These organisms are called
bisexual or hermophrodite.
For example, earthworm, leech, liverfluke, etc.
However, bisexual organisms are in number.
The organisms in which male and female
reproduc ve systems are present in different
individuals are called unisexual organisms. We
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and female sexes are separate are called
unisexual organisms.
For example, human beings, birds, rep les, fish,
etc.
FERTILISATION
There are two kinds of fer lisa on. These are:
v External fer lisa on
v Internal fer lisa on
External Fer lisa on
You will be surprised to know that there are
certain animals in which fer lisa on (fusion of
male and female gametes) takes place out side
the body of the female parent. This type of
fer lisa on in which the fusion of a male and a
female gamete takes place outside the body of
the female is called external fer lisa on. Such
type of external fer lisa on is common in many
amphibians, like, fish, star fish, etc.
You should remember that external fer lisa on
takes place in water.
Process of External Fer lisa on
Let us study about the process of external
fer lisa on by the example of a frog.
During rainy season frogs move to ponds or
slow moving streams.
The male and female frogs come together in
water. The female frog lays hundred of eggs.
These eggs do not have hard shell like other eggs
have. The eggs of female frog have a layer of jelly
that provides protec on to the eggs.
Science-8