Reproduction Part-1 For Class 8th Science

Need of reproduction

• Reproduction is essential for the continuation of species
• If there is no new individual is born but the death is continued ,You can imagine what will happen
• The Species which don’t reproduce may be perished in longer run

Modes Of Reproduction

There are two modes of reproduction

1. Sexual Reprodution
2. Asexual Reproduction

Sexual reproduction– is a mode of reproduction where fusion of two cells called gametes (Male and female) usually coming from two parents .

Example- Fish Frog Cow Dog Human etc.

Asexual Reproduction- Is a mode of reproduction which does not involve fusion of gametes or new individuals are produced from a single parent.

Example-amoeba ,Yeast Hydra

Sexual Reproduction in animals

• In animals some lays eggs and some give birth to young ones.

Example – In Butterfly ,the eggs are laid on the leaves.

From these eggs comes out caterpillar

After some time the caterpillar change into immobile pupa. The pupa changes into adult butterfly.

 

• The animals which lay eggs are called Oviparous animals.( Eg. Hen,Fro Butterfly Etc.)
• The animals which give birth to young ones are called Viviparous animals.(Human,Dog cat Etc.)

Gametes-

• Male gametes or sperms are produced in an organ called testes.
• Female gametes or egg or ovum are produced inside ovary.

If the two type of gametes present in single/same individual . These organism are called bisexual or hermaphrodite.

Example- Earthworm, Leeches

If the two type of gametes present in different individuals . These organism are called uni-sexual.

Example- Frogs ,Bids , Humans etc.

Fertilization-

When the sperm(from male partner) and ovum(from female partner) fuse together,a new cell, called zygote is formed.

The process of fusion of male and female gametes (Sperm and Ovum/eggs) is called Fertilization.

 

There are  two different ways of fertilization.

1. External Fertilization
2. Internal Fertilization

External Fertilization- When fusion of male and female gametes occur outside the body of female partner,the fertilization is called external fertilization.

Example- In Frog and fishes, The male and female partner release their gametes in water,and fertilization takes place in water.

Internal Fertilization-When the fertilization or fusion of gametes takes place inside the female body , the fertilization is called internal Fertilization

Examples- In Humans,Dogs,Cats, Hens etc.