Reproduction in Animals class 8 notes: Class 8 science ch 6 notes
| Textbook | Ncert |
| Class | Class 8 |
| Subject | Science |
| Chapter | Chapter 6 |
| Chapter Name | Reproduction in Animals |
| Medium | English |
Are you looking for Class 8 Science chapter 6 notes? Now you can download Reproduction in Animals class 8 notes pdf from here. This chapter covers the basic concepts of reproduction in animals. It explains the two main types of reproduction – sexual and asexual. The chapter describes male and female reproductive organs and their functions. It discusses fertilization – internal and external. Key stages like development of embryo, zygote, and fetus are mentioned. The chapter also covers asexual reproduction methods such as budding and binary fission.
🧬 Reproduction :-
Reproduction is the process by which living organisms produce more living organisms of its own kind.
🔄 Modes of Reproduction :-
There are two modes by which animals reproduce. These are:
- 1️⃣ Sexual reproduction, and
- 2️⃣ Asexual reproduction.
🧑🤝🧑 (i) Sexual reproduction :-
The type of reproduction beginning from the fusion of male and female gametes is called sexual reproduction. Example: Humans, cats, and flowering plants like hibiscus reproduce sexually.
👤 (ii) Asexual reproduction :-
This type of reproduction in which only a single parent is involved is called asexual reproduction. Example: Hydra (by budding), amoeba (by binary fission), and potato (by vegetative propagation) reproduce asexually.
♂️ Reproductive Organs ( Male Reproductive Organs) :-
- Main Parts: The male reproductive organs include a pair of testes (singular, testis), two sperm ducts and a penis.
- Sperms: The testes produce the male gametes called sperms.
- Functions: Millions of sperms are produced by the testes.
- Structure of a Sperm: Though sperms are very small in size, each has a head, a middle piece and a tail.
- A sperm is a single cell with all the usual cell components.
♀️ Reproductive Organs (Female Reproductive Organs) :-
- Main Parts: The female reproductive organs are a pair of ovaries, oviducts (fallopian tubes) and the uterus.
- Functions: The Ovary produces female gametes called ova (eggs). In human beings, a single matured egg is released by one of the ovaries, into the oviduct every month. Uterus is the part where development of the baby takes place.
- Structure of an Egg: An egg is a single cell with all the usual cell components.
🧪 Ova and Sperms :-
The ovary produces female gametes called ova and the testes produce male gametes called sperms.
🔗 Fertilization :-
The fusion of ovum and sperm is called fertilisation The fertilised egg is called a zygote. There are two main types of fertilization:
- 1. Internal Fertilization
- 2. External Fertilization
🤰 Internal Fertilisation :-
Fertilisation that takes place inside the female body is called internal fertilisation. This is observed in human beings and other animals such as hens, cows and dogs.
🐸External Fertilisation :-
Fertilisation that takes place outside the female body is called external fertilisation. This is observed in frogs, fish, starfish, etc.
🧫 Test-Tube Babies IVF (In Vitro Fertilisation) :-
Sometimes, oviducts in women are blocked, preventing fertilization as sperms cannot reach the egg. In such cases, doctors use a method called IVF (In Vitro Fertilisation), which means fertilization outside the body.
Steps in IVF:
- Doctors collect freshly released egg and sperm are collected from the mother and father.
- They are kept together for a few hours to allow fertilization.
- If fertilization occurs, the zygote is allowed to develop for about a week.
- Then, the early-stage embryo is placed in the mother’s uterus.
- Complete development takes place inside the uterus, and the baby is born normally.
Test-tube babies :-
Babies born through this technique are called test-tube babies. This term is actually misleading because babies cannot grow in test tubes.
👶 Development of Embryo :-
- Fertilization leads to the formation of a zygote.
- The zygote divides repeatedly, forming a ball of cells.
- These cells group together to develop into different tissues and organs.
- This growing structure is called an embryo.
- The embryo gets embedded in the wall of the uterus.
- Further development of the baby takes place inside the uterus.
- The embryo continues to develop in the uterus.
- It gradually develops body parts such as hands, legs, head, eyes, ears etc.
- When the development of the foetus is complete, the mother gives birth to the baby.
Foetus :-
The stage of the embryo in which all the body parts are identifiable is called foetus.
🐮Viviparous animals :-
Animals such as human beings, cows and dogs which give birth to young ones are called viviparous animals.
🐣 Oviparous animals :-
Animals such as hen, frog, lizard and butterfly which lay eggs are called oviparous animals.
🐸 Life Cycle of a Frog :-
- There are three distinct stages, that is,
- Egg → Tadpole (larva) → Adult frog
- Tadpoles look completely different from adult frogs.
- Tadpoles later transform into frogs that can jump and swim.
🔄 Metamorphosis :-
The process of Frog transformation from larva to adult with drastic changes is called metamorphosis. Example: Frog (egg → tadpole → adult)
🌱 Budding :-
In hydra, new individuals develop from buds. This method of asexual reproduction is called budding.
Binary fission :-
Amoeba reproduces by dividing itself into two. This type of asexual reproduction is called binary fission.
🔁 Methods of Asexual Reproduction :-
1. Budding (in Hydra and Yeast):
Budding is a type of asexual reproduction observed in organisms like Hydra and Yeast. In this method, new individuals develop as small outgrowths, called buds, on the parent’s body. These buds grow gradually and eventually detach to become separate individuals. Since this process involves only a single parent and no involvement of gametes, it is categorized as a form of asexual reproduction.
2. Binary Fission (in Amoeba):
Binary fission is commonly seen in Amoeba, a microscopic single-celled organism. In this process, the nucleus of the parent amoeba divides into two, followed by the division of the body into two parts. Each part receives one nucleus and grows into a new amoeba. Thus, one parent cell gives rise to two identical daughter cells. This method of reproduction, where an organism splits into two, is known as binary fission.
Other Methods:
- There are other asexual methods of reproduction like:
- Fragmentation
- Spore formation
- Vegetative propagation (in plants)
- These will be studied in higher classes.
🧬 Cloning :-
Cloning is the creation of an organism that is an exact genetic copy of another. This means that every single bit of DNA is the same between the two organisms