8th Reproduction in animals

November 30, 2021

Class 8th Science

ICSE/ CBSE Notes-

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Reproduction of Animals

In the Earth living organism is dead after some time.
No living organism is permanent on the Earth.
For the continuation of life on the earth it is essential to reproduce life.
Reproduction is important for the growth of population of any species

Type of reproduction

There are mainly two types of way of production

Asexual Reproduction
Sexual Reproduction

Asexual Reproduction-

In this type of Reproduction one individual is capable of reproducing another individual. This kind of reproduction is known as Asexual Reproduction.

Reproduction in amoeba takes place through binary fission.
In binary fission the nucleus divided ,then new individual create.
Asexual Reproduction organism does not required sexual cells.

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2-Sexual Reproduction

In this type of Reproduction male and female sex cells are required .
Male and Female sex cells are known as gametes from the two parents unite to form a zygote.
In Most animal and plants sexual reproduction takes place.
Animals and plants have different organs that produce the male and female gametes.

Male Reproductive Organs

Male reproductive organs consists following terms.

Testes
The sperm ducts

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Testes

It is placed inside the scrotal sacs outside the abdominal cavity.
Testes produce millions of male gametes known as sperms.

Sperms

These are very small in size
Each sperm is a single cell consisting of a head and tail with middle portion.

The sperm ducts or vas deferens

It is a tube by which the sperms reach the penis from the testes.

Penis

This is a muscular structure which transfers the sperms inside the female reproductive system

Female Reproductive Organs

The main female reproductive organs are given as below

Ovaries
Oviducts or fallopian tubes
Uterus
Vagina

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Ovaries

Ovaries is an important part of female reproductive organs.
Ovaries are present in pair. it is two in number.
These are situated in the lower abdominal cavity.
Ovaries produces a single celled egg or an ovum every month.

2 Oviducts or fallopian tubes

Oviducts or fallopian tubes are connect the ovaries to the uterus.
It transfer the ovum from the ovary to the uterus.

3 Uterus

This is a muscular structure.
Uterus take place for the development of foetus.

4 Vagina

It is a muscular tube through which the uterus opens to the outside

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Fertilization

The fusion of Sperms and an Ovum is known as fertilization.
Fertilization is the process of reproduction.
fertilization is the first step of beginning of reproduction.

For fertilization these components are take main role

Ovum
Sperms

Ovum

Ovum is a reproductive cell in female .
A mature female reproductive cell is called Ovum.
The Ovum contributes one chromosome of each pair to the fertilized cell

Sperms

Sperms is the male reproductive cell.
It is used for production of new one.
Sperms is the smallest cell of the human cells.

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Types of Fertilization

Fertilization may be either External or internal

External Fertilization
Internal Fertilization

1-External Fertilization

when the fusion of the sperm and the ovum take place outside the body of the female it is known as external fertilization.

Eg- Fish ,frog,toads are the example of external fertilization

2-Internal Fertilization

When the fusion or fertilization take place inside the body of the female this is known as internal fertilization

Different animals have different size of egg
The ostrich egg is largest egg
In human the male sperms are released inside the vagina.

NOTE-

Animals that lay eggs are called OVIPAROUS animals.
Animals that give birth to young ones are called VIVIPAROUS animals.
The egg or ovum is released by the ovary and reaches the oviduct.
one of the sperms that reach the oviduct fuses with egg and fertilizes it and make forms Zygote.
The nuclei of the sperms and the ovum unite and give rise to a single nucleus.

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Development of Embryo

The zygote further undergoes repeated divisions and gives rise to ball of cells that form groups and develops into different tissues and organs of body. This structure is called embryo.
It develops the different body parts like hands, legs, eyes, ears, nose, etc. this phase of embryo when it has developed all its body parts is called foetus

Viviparous Animals

Those animals who give birth to young ones are known as Viviparous Animals.
Most mammals give birth to their young one.
Human , animals like cow ,dog , horse etc

some exceptions like the spiny ant eater or the echidna and platypus which gives egg.

platypus

Echidna gives egg

Oviparous Animals

Those animals who gives EGG are called oviparous Animals
Like birds ,reptiles and insects .
The birds are egg lying animals but their egg are fertilized internally.
After fertilization the number of protective layers are formed around the zygote

Metamorphosis