Notes of Ch 9 Reproduction in Animals| Class 8th Science

Study Material and Notes of Ch 9 Reproduction in Animals Class 8th Science

Topics in the chapter

• Male Reproductive System
• Female Reproductive System
• Fertilization
→ Internal fertilization
→ External Fertilization
• Test tube baby
• Fertilization in Humans
• Asexual reproduction
→ Budding
→ Fission
→ Cloning
• Oviparous animals
• Viviparous animals
• Metamorphosis
• Lifecycle of silkworm
• Hormone responsible for metamorphosis in insects

Male Reproductive System


→ It consists of testis, sperm duct and penis.

→ Testes are involved in the production of male gametes called sperms.

→ Millions of sperms are produced by the testes.

→ Each sperm consists of three parts: Head, middle piece and tail.

Female reproductive system


→ It consists of ovaries, oviduct and uterus.

→ Ovaries produce ova or eggs.

→ A single matured egg is released from ovary into oviduct every month.

→ Baby develops in the uterus.

→ Egg is also single celled like sperm.

Fertilization

→ The process of fusion of male and female gametes (egg and sperm) to form zygote is known as fertilization.

→ It is of two types:
(i) Internal fertilization
(ii) External fertilization

Internal fertilization

→ In this, the fusion of sperm and egg takes place inside the female's body.

→ It occurs in cows, dogs and humans.

External fertilization

→ In this, the fusion of sperm and egg takes place outside the female's body in a surrounding medium, generally water.

→ It occurs in frogs, fishes, starfish, etc.

Test tube baby

→ A baby conceived by fertilization that occurs outside the mother’s body is called test tube baby.

→ Development of the embryo

→ The zygote repeatedly divides to form a ball of cells.

→ The ball of cells then starts differentiating into tissues and organs. At this stage, it is called embryo.

→ Embryo gets attached to the wall of the uterus and develops various body parts such as hands and legs.

→ Foetus is a stage of embryo that shows main recognizable feature of mature organism.

→ Foetus develops for nine months inside the mother’s womb and is finally delivered.

Fertilization in Humans


→  Fusion of the nucleus of the sperm with the ovum to form a zygote. It occurs in the fallopian tube of females.


→ Zygote divides to form an embryo.


→ Embryo is implanted in the uterus.


→ Foetus develops inside the mother’s body for nine months (gestation period).

Asexual reproduction

→ The type of reproduction which involves only a single parent and the new individuals are formed without the fusion of gametes is known as asexual reproduction.

• Three common methods of asexual reproduction are:
(i) Budding
(ii) Fission
(iii) Cloning

Budding

→ It involves the formation of new individual from the bulging of the parent body.


→ This phenomenon is very common in plants, fungi and animals such as Hydra and yeast.

Fission


→ Binary fission is the type of asexual reproduction that occurs in Amoeba.

→ It is a type of asexual reproduction in which a single cell divides into two halves.

Cloning


→ Cloning is the process used to create an exact copy of a cell, tissue or an organism.

→ Dolly, a sheep was the first mammal to be cloned. It was cloned by Ian Wilmut and his colleagues in 1996.

Oviparous animals

→ The animals that lay eggs are called oviparous animals.


→ The examples include all kinds of birds, lizards, snakes, and frogs.

Viviparous animals

→ The animals that give birth to young ones are called viviparous animals.

→ The examples include cows, dogs, and humans.

Metamorphosis

→ The biological process of transformation of larva into an adult is known as metamorphosis.

• The life cycle of frog consists of the following stages:
Egg → Tadpole (larva) → Adult

→ Hormones controlling metamorphosis in frogs

→ Thyroxin (produced by the thyroid gland) initiates the process of a tadpole’s metamorphosis into an adult frog.

→ In the absence of thyroxin, the tadpole does not transform into an adult and remains in the tadpole stage.

Life cycle of silkworm

→ Silkworm grows on mulberry trees and feeds on its leaves.

→ During a stage in its life cycle, silkworm spins a cocoon around itself.

→ Silk is obtained from this cocoon.

Hormone responsible for metamorphosis in insects

→ In insects, metamorphosis is controlled by the insect hormones. Some of the insect hormones are:
(i) Prothoracicotropic Hormone (PTTH)
(ii) Ecdysone
(iii) Juvenile Hormone (JH)

GET OUR ANDROID APP

Get Offline Ncert Books, Ebooks and Videos Ask your doubts from our experts Get Ebooks for every chapter Play quiz while you study

Download our app for FREE

Study Rankers Android App Learn more

Study Rankers App Promo