Notes of chapter: Reproduction in Animals are presented below. Indepth notes along with worksheets and NCERT Solutions for Class 8.
Reproduction is a process in which male and female adults produce similar young ones.
Eg:- Human produces babies who looks like humans.
Name of the young ones of different animals are tabulated below:-
|4.||Butterfly||Pupa or caterpillar|
Types of reproduction-
(i) Sexual reproduction-
Sexual Reproduction is a process in which male and female gametes are fused to form zygote which develops into a new individual.
Sexual reproduction in viviparous animals(Humans)
Male reproductive part –
(a)The male reproductive organs are two testes, two sperm ducts and a penis.
(b) The sperm is single celled male gametes which are produced by the testes in millions.
Sperm is very small in size. They have head, middle piece and a tail. The tail is very helpful in the movement.
Female reproductive organs-
(a) The female reproductive parts are a pair of ovaries, oviducts (Fallopian tubes) and the uterus.
(b) Ova (eggs) is a single celled female gametes (reproductive cells) which is produced by the ovary. A single matured egg is released into the oviduct by one of the ovaries every month.
(c) Babies developed in the uterus.
(a) The process in which nuclei of egg from the female and the nuclei of sperm from the male fused to form a fertilized egg or zygote is called fertilisation. Internal fertilisation takes place in viviparous animals.
Zygote is a fertilized egg which forms during the fusion of nuclei of egg from the female and the nuclei of sperm from the male.
(b) An individual looks like his or her parents because an individual created when egg from mother meets with sperm of father. All brother and sisters have similar characteristics and facial features.
Types of fertilisation-
(a) The process of fertilisation which takes place inside the female body is called internal fertilisation. This type of fertilisation takes place in viviparous animals.
Eg:- Human, cow, dog,etc.
The process in which fusion of female egg and male sperm takes place in the out side the body is called in vitro fertilisation (IVF).
When oviducts of some women blocked or male have less sperm count, sperm can not reach to egg for fertilisation. In these conditions doctors collect freshly released egg and sperm and keep them together for fusion (IVF). After fertilisation zygote is allowed to develop for a week. Then it is placed in mother’s uterus where zygote develop completely and a baby born.
The baby who is born with in vitro fertilisation is called test tube baby. The baby is called test tube baby because fusion takes place out side female body but zygote develops inside the body.
(b) The process of fertilisation which takes place outside the female body is called external fertilisation. This type of fertilization takes place in oviparous animals.
Eg:- Fish, frog and aquatic animals.
The female of frog lays hundreds of egg in pond or slow flowing streams. These eggs are not covered with shell. They are very delicate and hold by a layer of jelly for protection. Male frog deposits sperms over the eggs. Each sperm can swim in the water with the help of its long tail. The sperm come in contact with eggs and process of fertilisation happen. But, not all egg converts into new individual.
Reasons of not converting all egg into new individuals-
(a) Eggs and sperms get exposed to water movement.
(b) Some times, eggs and sperms destroyed by the wind and rainfall.
(c) Sometimes, eggs are eaten by the other animals of the pond.
All these reasons also support production of eggs and sperms in large number.
Development of Embryo-
(a)The stage of development of unborn baby where an fertilized egg or zygote divides and begin develops as baby, is known as embryo.
After fertilisation zygote continuously divides to give rise to small group of cells which begin to form different tissues and organs of the body like hand, face, legs etc. This developing structure is termed an embryo. The embryo gets embedded in the wall of uterus for further development.
(b)The stage of the embryo in which all the body parts are identifiable is called foetus.
Sexual reproduction in oviparous animals
In oviparous or the animals which undergo external fertilisation, egg came out through oviduct after fertilisation.
After the fertilization in the oviparous animals the zygote divides repeatedly and travels down the oviduct with many protective layers. When zygote has a hard shell like protective layer the egg came out from the oviparous animals. The embryo of egg develops inside the egg shell. The embryo of a hen takes about 3 weeks to devlop into a chick. The hen sits on the egg to provise warmth to the egg. When the development of the chick takes place inside the egg shell the chick bursts open the egg shell.
Development of embryo-
Development of the embryo takes place outside the female body. The embryo continues to grow with in their eggs coverings. After the embryo develops the egg hatches.
Metamorphosis is a process in which animal structure changes drastically after their birth.
Eg:- Frog, silk worm etc.
The young ones develop in to adults. The young ones of viviparous animals look like their parents. But in some oviparous animals young ones looks different from their patterns.
Life cycle of silk worm
Egg – larva – pupa – adult (Moth)
Moth is completely looks different from larva or caterpillar.
Life cycle of frog
Egg – early tadpole – late tadpole – frog
Frog is completely looks different from tadpole.
(ii) Asexual Reproduction-
When process of reproduction is completed by only a single parent is called asexual reproduction.
Types of asexual reproduction-
(a) When a new individual is born or develops from the buds or outgrouth, is called budding.
Bulges of hydra are known as buds. Parent hydra develops a bump which grows and separate from the parent hydra as independent hydra.
(b) When a microscopic organism divides its nucleus in two parts, each part has its own nuclei, is known as binary fission.
Amoeba begins the process of reproduction by the division of its nucleus into two nuclei. The body of parent amoeba is divided into two parts with nucleus in each part. The body parts separates from the parent amoeba are known as daughter amoebae.
(2) Cloning is a process in which clone of a cell or a complete organism is copied exactly.
It was first done by Ian Wilmut and his colleagues at the Roslin Institute in Edinburgh.
They successfully cloned a sheep on 5 July 1966.
They collected a cell from a female of Finn Dorsett sheep. They also take an egg from a Scottish blackface ewe. The nucleus of the egg was removed. The nucleus of the Finn Dorsett sheep is transferred in to the egg of the Blackface ewe. After the development of the egg the sheep had born which is named “Dolly”.
She shows resemblance and characteristics of the Finn Dorsett Sheep whose nucleus was used in the development of the dolly. She gave birth to many young ones by normal sexual reproduction. But, she died on 14 February2003 due to a lung disease.