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Class 8 Science NCERT-Biology Lesson 5
Chapter 9 Reproduction in Animals
Reproduction is essential for the continuation of a species. It ensures the continuation of similar kinds of individuals, generation after generation. Modes of Reproduction: ** Just as in plants, there are two modes by which animals reproduce. These are: (i) Sexual reproduction, and (ii) Asexual reproduction. Sexual Reproduction: Plants that reproduce sexually have male and female reproductive parts. In animals also, males and females have different reproductive parts or organs. form a zygote. It is the zygote which develops into a new individual called sexual reproduction. *Like plants, the reproductive parts in animals also produce gametes that fuse to * This type of reproduction beginning from the fusion of male and female gametes is
Male Reproductive Organs *The male reproductive organs include a pair of testes (singular, testis), two sperm ducts and a penis. The testes produce the male gametes called sperms. Millions of sperms are produced by the testes. Though sperms are very small in size, each has a head, a middle piece and a tail. Each sperm is a single cell with all the usual cell components Female Reproductive 0 *The female reproductive organs are a pair of ovaries, oviducts (fallopian tubes) and the uterus. Ovary produces female gametes called ova (eggs) In human beings, a single matured egg is released into the oviduct by one of the ovaries every month. Like the sperm, an egg is also a single cell. Uterus is the part where development of the baby takes place.
Male Reproductive System Pubic bone Fallopian tubes Ovaries Uterus Bladder Seminal vesicle Ductus deferens Prostate gland Penis Cervix Epididymis Testis Scrotum Spongy urethra Vagina
Human sperm: Acrosome Pasma membrane Mitochondri Nucleus Axial filament Centriole Terminal disc Head Mid (connecting) piece Tail End piece Peri-acrosomal space Sub-acrosomal space Cell membra uclear envelope Acrosom Nuclear vacuo Nucleu uter acrosome membrane quatorial segment Post-acrosoma region ost-acrosom sheath osterior rin entriole Redundant nuclear envelope Centriole onnecting Pie tochondria sheath uter dense fibe entral Pair Axoneme Axoneme FRONT VIEW SIDE VIEW
Fertilization: ** The first step in the process of reproduction is the fusion of a sperm and an ovum When sperms come in contact with an egg, one of the sperms may fuse with the egg. Such fusion of the egg and the sperm is called fertilization ** During fertilization, the nuclei of the sperm and the egg fuse to form a single nucleus. This results in the formation of a fertilized egg or zygote. The zygote is the beginning of a new individual. * The process of fertilization is the meeting of an egg cell from the mother and a sperm cell from the father. So, the new individual inherits some characteristics from the mother and some from the father. ** Fertilization which takes place inside the female body is called internal fertilization. Internal fertilization occurs in many animals including humans, cows, dogs and hens
Sperm Ovun Fertilizatior Fusing nuclei Zygote
There are some women whose oviducts are blocked. These women are unable to bear babies because sperms cannot reach the egg for fertilization. * In such cases, doctors collect freshly released egg and sperms and keep them together for a few hours for IVF or in vitro fertilization (fertilization outside the body) fobout a week and <* In case fe then it is placed uterus and the baby is born like any other baby in the mother's uterus. Complete development takes place in the * Babies born through this technique are called test-tube babies. This term is actually misleading because babies cannot grow in test tubes.
Fertilisation in frogs: ** In many animals fertilization takes place outside the body of the female. In these ** During spring or rainy season, frogs and toads move to ponds and slow flowing animals, fertilization takes place in water streams. When the male and female come together in water, the female lays hundreds of eggs. ** Unlike hen's egg, frog's egg is not covered by a shell and it is comparatively very delicate. A layer of jelly holds the eggs together and provides protection to the eggs. ** As the eggs are laid, the male deposits sperms over them. Each sperm swims randomly in water with the help of its long tail. The sperms come in contact with the eggs. This results in fertilization This type of fertilization in which the fusion of a male and a female gamete takes place outside the body of the female is called external fertilization. It is very common in aquatic animals such as fish, starfish, etc