These DAV Class 8 Science Notes and DAV Class 8 Science Chapter 14 Notes – Reproduction in Animals act as excellent revision resources, particularly in preparation for board exams.
Reproduction in Animals Class 8 DAV Notes
→ Reproduction: The process by which a living being produces its offspring is called reproduction. Reproduction in animals is of two types:
A. Asexual Reproduction: When a single parent is involved and no gamete formation takes place, the reproduction is called asexual reproduction. Asexual reproduction takes place by following methods:
→ Binary Fission: This method is observed in unicellular organisms. During binary fission, the parent cell divides into two daughter cells. Examples: Bacteria and Amoeba.
→ Multiple Fission: A repeated division of the parent cell takes place which results in the production of a number of small individuals, e.g. plasmodium.
→ Budding: In this method, a small protuberance is formed on the body of the parent. This is called bud. The bud grows to a certain size and then gets detached from the parent’s body. This finally develops into a new individual, e.g. hydra and yeast.
B. Sexual Reproduction: In sexual reproduction, two parents are involved. Two types of gametes, i.e. male and female, is formed by the respective parents. The gametes fuse through a process; called fertilisation.
→ Gametes: Specialised cells formed by male and female parents which take part in sexual reproduction. The male gamete is called sperm and female gamete is called ova; in multicellular animals.
→ Fertilisation: Fusion of male and female gametes is called fertlisation.
→ Zygote: The product of fusion of male and female gametes is called zygote.
→ Hermaphrodite Animal: When both the sexes are present on the same individual, the animal is called hermaphrodite.
→ Types of Fertilisation
→ External Fertilisation: When fertilisation takes place outside the animal’s body, it is called external fertlisation. Example: Frogs, fishes.
→ Internal Fertilisation: When fertilisation takes place inside the animal’s body, it is called internal fertilisation. Examples: humans, crocodiles, birds, etc.
→ External Development: When the embryo develops outside the animal’s body, it is called external development. External development is the norm in case of external fertilisation. In case of internal fertilisation, external development is seen in some animals; which lay eggs.
→ Internal Development: When the embryo develops inside the animal’s body, it is called internal development, e.g. Mammals.
→ Oviparous Animals: Animals which lay eggs are called oviparous animals, e.g. reptiles, and birds.
→ Viviparous Animals: Animals which give birth to young ones are called viviparous animals, e.g. most of the mammals.
Human Reproductive System
→ Male Reproductive System:
The male reproductive system is composed of a pair of testes, two sperm ducts, urethra and a penis. Testes are oval in shape and are present outside the body in a skin pouch; called scrotum.
The sperm is produced by the testes. From the testis, the sperms pass through the sperm ducts to the urethra. The penis is a muscular organ which provides a passage to urine and semen.
Structure of a Sperm: The sperm is composed of three parts, viz. a head, middle piece and a tail. A structure are the tip of the head produces an enzyme which helps the sperm to penetrate the ovum.
→ Female Reproductive System:
The female reproductive system is composed of a uterus, a pair of ovaries and a pair of oviducts. Uterus is a muscular organ which is in the shape of a pouch. The foetus develops inside the uterus. The uterus opens on the outside through an opening called vagina.
→ Fertilisation: The sperms enter through the vagina and travel to the oviduct. Fusion of male and female gametes takes place in the oviduct. The zygote; formed after the fertilisation is single-celled structure.
→ Development of Embryo: The zygote undergoes repeated cell division and turns into a ball like cluster of cells. This is called embryo. The embryo gets implanted in the wall of the uterus. The embryo develops further and a stage comes when it begins to resemble a human being. At this stage, it is called a foetus.
→ Egg Formation in Hens: When the zygote begins to travel down to the uterus; in a hen; many protective layers are formed around it. One of the protective layers forms the egg shell. The shell is made of a form of calcium carbonate; which is called calcite. The egg is then laid by the hen. The embryo inside the egg takes about 21 days to develop into a chick. The hen sits on the eggs to provide warmth. This process is called incubation. The chick breaks open the shell and comes out of the egg. This process is called hatching.
→ Metamorphosis: In some animals, the young ones do not look like the adults. The young one undergoes a series of change to turn into an adult like animal. This process is called metamorphosis. This type of development is called indirect development. Indirect development can be seen in frogs in which a tadpole develops into a frog.
→ Gamete : Specialised cells which take part in sexual development.
→ Zygote : The product of fertilisation.
→ Embryo : The multicellular stage after the zygote.
→ Foetus : When an embryo begins to resemble an dufl animal, it is called a foetus.
→ Gestation : The perioa from pregnancy o cld rth is called gestatior.
→ Metamorphosis : A series ot changes ira which a young one changes into adult-like animal.