Class 8 Science Chapter 9 Notes Reproduction in Animals Notes

In this post, we will discuss Class 8 Science Chapter 9 notes Reproduction in Animals Notes. Class 8th science ch 9 notes help students in revision. Reproduction in Animals notes class 8, we will learn about how reproduction takes place in the animal. You can also download the Reproduction in Animals notes class 8 pdf for further study. NCERT notes for the Class 8 Science Chapter 9 are designed by our subject expert team.

In this Class 8th Science, Ch 9 Notes pdf, we will learn about the Reproduction in Animals.

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Class 8 Science Chapter 8 notes Overview

Do you recall the process of digestion circulation and respiration which we study in the previous class? This process is essential for the survival of every individual. We also learn about the process of reproduction in plants. Reproduction is essential for the continuation of a species.

Mode of Reproduction

Just as plants, there are 2-modes of reproduction.

  1. Sexual Reproduction
  2. Asexual Reproduction
sr.noAnimalyoungs one
1humanbaby
2catkitten
3dogpup
4butterflylarvae
5henchick
6cowcalf
7frogfroglet
table 9.1

Sexual Reproduction

Male and females have different reproductive parts or organs. Animals also produce gametes that fuse to form a zygote. This zygote develops into a new individual.

The reproduction begins from the fusion of male and female gametes and is called sexual reproduction

Now we study the Reproductive parts of the human

Male Reproductive Organ

The male reproductive organs include a pair of testes, 2- sperm ducts and a penis. The testes produced the male gametes (sperm) called sperm. Millions of sperm are produced by the testes.

Class 8 Science Chapter 9 Notes Male reproductive organs in humans
Male reproductive
organs in humans

The sperms are very small in size. Each sperm has a head, a middle piece and a tail. Sperm is a single cell with all the usual cell components.

Human Sperm
Human Sperm

Female Reproductive Organs

Female reproductive organs in
humans
Female reproductive organs in
humans
  • The female reproductive organs are a pair of ovaries, oviducts (fallopian tubes) and uterus.
  • The ovary produces female gametes called ova (egg). A single mature egg is released into the Oviduct by one of the ovaries every month.
  • The uterus is a part where the development of the baby takes place.
  • Like the sperm and egg is also a single cell.

Fertilisation

  • The first step of reproduction is the fusion of sperm (male gametes) and ovum (female gametes). When sperm comes in contact with an egg (ovum), one of the sperm may fuse with the egg. Such fusion of egg (ovum) and sperm is called fertilization.
  • During fertilization, nuclei of sperm and egg fuse to form a single nucleus known as fertilized egg or zygote.
fertilisation
fertilisation
Zygote
Zygote
  • Fertilization which takes place inside the female body is called internal fertilization. Internal fertilization takes place in humans, cows, dogs and hens etc.
  • Fertilization which cannot occur inside the female body or fertilization outside the female body is called external fertilization. In many animals, fertilization takes place in water example frogs, Starfish, fish etc

External fertilization in frogs

  • During spring or a rainy season, frogs and toads move to ponds and slow-flowing streams. When male and female come together in water, the female ley 100 eggs.
  • A layer of jelly holds the egg together and provides protection.
  • As the egg is laid, the male deposits sperm over them. Each sperm swims randomly in water with the help of a long tail. The sperm comes in contact with the eggs this result in fertilization.

Why do fish and frogs lay eggs in hundreds?

  • The female frog Lays hundred of eggs and males release million of sperms, all the eggs do not get fertilize and develop into a new individual.
  • This is because the egg and sperm get exposed to water movement, wind, rainfall and other water animals feed on the egg.
  • Thus, to ensure fertilisation, the large number of eggs or sperm produced by fish and frogs.

have you heard of test-tube babies?

  • In some women, Oviducts are blocked. These women are unable to bear babies because sperm cannot reach the egg for fertilization.
  • In such cases, doctors collect freshly release eggs and sperms and keep them together for a few hours for IVF or in vitro fertilization (fertilization outside the body)
  • In case fertilization occurs, the zygote is allowed to develop for about a week and then place in the mother’s uterus.
  • Now complete development takes place in the uterus like other babies.
  • Babies born through this technic are called test-tube babies.

Development of Embryo

Fertilization results in the formation of the zygote. after the zygote embryo is developed. The zygote divides repeatedly to rise a ball of cells (2 cells) after that the cell then begins to form a group of cells that develops into a different tissue and organ of the body. This developing structure is termed an embryo. This embryo gets embedded in The Wall of the uterus for further development.

Zygote formation and development of an embryo from the zygote; (b) Ball of cells; (c) Embedding of the embryo in the uterus
(a) Zygote formation and development of an embryo from the zygote; (b) Ball of cells; (c) Embedding of the embryo in the uterus

The embryo is continuously developing in the uterus. It gradually develops body parts such as hand, leg, head, eye etc. This stage of the embryo in which all the body parts are formed is called a foetus. When the development of the foetus is complete, the mother gives birth to the baby.

Viviparous and Oviparous Animal

  • Viviparous animal:- The animal which gives birth to the young ones are called Viviporus animals.
  • Oviparous animal:- The animal which lay eggs are called oviparous animals.

Asexual Reproduction

The reproduction in which only a single parent is involved is called Asexual reproduction. example Hydra and amoeba.

Asexual Reproduction in hydra

Budding in Hydra
Budding in Hydra

In hydra, there may be one or more bugs. These bugs then develop new little hydra they are called bugs full stop the new individual develops from the bug in hydra this type of Asexual reproduction is called budding.

Asexual reproduction in amoeba

Binary fission in Amoeba Class 8 Science Chapter 9 Notes
Binary fission in Amoeba
  • Amoeba is a single-cell organism. The reproduction in Amoeba begins by the division of its nucleus into two nuclei and after that, each nucleus gets separated and the daughter amoeba is produced.
  • This type of asexual reproduction in which an animal reproduce by dividing into two individual is called Binary fission.

What we learn in Class 8 Science Chapter 9 Notes Reproduction in Animals Notes

In Class 8th Science Ch 7 Notes pdf / Reproduction in Animals Notes

  • There are two modes by which animals reproduce. These are (i) Sexual reproduction, and (ii) Asexual reproduction.
  • Reproduction resulting from the fusion of male and female gametes is called sexual reproduction.
  • The reproductive organs in the female include the ovaries, oviducts and uterus.
  • The reproductive organs in males include the testes, sperm ducts and penis.
  • The ovary produces female gametes called ova and the testes produce male gametes called sperms.
  • The fusion of the ovum and sperm is called fertilisation. The fertilized egg is called a zygote. Fertilization that takes place inside the female body is called internal fertilization. This is observed in human beings and other animals such as hens, cows and dogs.
  • Fertilization that takes place outside the female body is called external fertilization. This is observed in frogs, fish, starfish, etc.
  • The zygote divides repeatedly to give rise to an embryo.
  • The embryo gets embedded in the wall of the uterus for further development.
  • The stage of the embryo in which all the body parts are identifiable is called the foetus.
  • Animals such as human beings, cows and dogs which give birth to young ones are called viviparous animals.
  • Animals such as hens, frogs, lizards and butterflies which lay eggs are called oviparous animals.
  • The transformation of the larva into an adult through drastic changes is called metamorphosis.
  • The type of reproduction in which only a single parent is involved is called asexual reproduction.
  • In hydra, new individuals develop from buds. This method of asexual reproduction is called budding.
  • Amoeba reproduces by dividing itself into two. This type of asexual reproduction is called binary fission.

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