Reproduction in Animals PDF

# Reproduction in Animals ## Session - 1: How Do Organisms Reproduce? ### Objectives - To understand why reproduction in organisms is essential. - To know the different modes of reproduction. ### Before You Start #### You Should Know The processes of digestion, circulation, and respiration are es...

# Reproduction in Animals ## Session - 1: How Do Organisms Reproduce? ### Objectives - To understand why reproduction in organisms is essential. - To know the different modes of reproduction. ### Before You Start #### You Should Know The processes of digestion, circulation, and respiration are essential for the survival of every individual. Reproduction is essential for the continuation of a species. #### Check-in - Is reproduction essential for the survival of the individual? - How does reproduction help in the continuation of a species? ### Reproduction All of us will eventually grow old and die. The same applies to other organisms too. Even as organisms grow old and die, there are new ones born. This happens because of reproduction. The production of new organisms from the existing organisms of the same species is known as reproduction. The ability of living organisms to reproduce more members of their species is one of their most essential traits. To ensure the survival of their species, living beings reproduce more of their kind. Reproduction ensures the continuity of life on earth. Humans give birth to babies. These babies grow up and become adults and eventually give birth to more babies, and the process goes on and on. More organisms with the same basic characteristics as their parents are produced through reproduction. Humans always give birth to human babies. Cows always produce calves, cats always produce kittens, and hens always produce chicks. In this session, we will know more about the modes of reproduction. The newly born animal is called a young one. Babies, calves, and chicks are the young ones. ### Modes of Reproduction There are many different ways in which new organisms are produced from their parents. Some organisms like yeast, grow out of the parent's body in the form of a bud, and eventually separate from the parent and become a new individual. Amoeba can split into two, and each grows out to be a new individual. Birds and snakes hatch out of the eggs, laid by their parents. Human babies, kittens, calves, and joeys are born from their mothers. Each species of organism produces its young in a different way. ___ Just as in plants, there are two modes by which animals reproduce. These are sexual reproduction, and asexual reproduction. ## Asexual Reproduction Asexual reproduction is the process of creating new organisms from a single parent without the use of sex cells. As there is no involvement of sex cells, the process is called asexual reproduction. Binary fission in amoeba, budding in Planaria, and spore formation in Mucor are some of the ways animals reproduce asexually. Asexual reproduction is the simplest form of reproduction, most commonly seen in the lower organisms. In asexual reproduction, the young ones are the exact copy of their parents. ## Sexual Reproduction Sexual reproduction is the process of creating new organisms from two parents using their sex cells. In sexual reproduction, one parent's sex cell fuses with the other parent's sex cell to generate a new cell called the zygote. The zygote formed grows and develops into a new organism. The two parents involved are the male and female respectively. The male and female parents have special organs where the male sex cells and female sex cells are produced in male and female parents respectively. Humans, cats, dogs, monkeys, fishes, elephants and many more animals reproduce sexually. ### How is sexual reproduction different from asexual reproduction? In asexual reproduction, only one parent is involved, whereas two parents are involved in sexual reproduction. There are no sex cells involved in asexual reproduction. There are 2 sex cells involved in sexual reproduction. ### Word Help - **Reproduction**: The production of new organisms from the existing organisms of the same species is known as reproduction. - **Asexual reproduction**: Asexual reproduction is the process of creating new organisms from a single parent without the use of sex cells. - **Sexual reproduction**: Sexual reproduction is the process of creating new organisms from two parents using their sex cells. ## Session - 2: Male Reproductive Organs & Female Reproductive Organs ### Objectives - To understand the structure and function of male and female reproductive organs. ### Before You Start #### You Should Know Sexual reproduction is the process of creating new organisms from two parents using their sex cells. The parents have special organs where the male sex cells and female sex cells are produced in male and female parents respectively. #### Check-in - Which animals reproduce sexually? Give examples. - How do we differentiate the male and the female? ### Male and Female There are two parents involved in the process of sexual reproduction - a male and a female. Each parent has sex organs which help in the production of sex cells or gametes. The male parent has *testes* which produce male sex cells called the *sperms*. The female parent has *ovaries* which produce female sex cells called the *eggs*. Sexual reproduction in animals includes the formation of sperms and eggs in the parent's body, fusion of the sperm with the egg to form a zygote through fertilization and the growth and development of the zygote to form a baby animal. ## Sexual Reproduction in Humans ### The Male Reproductive System The human male reproductive system consists of the testes, scrotal sacs, epididymis, sperm ducts, seminal vesicles, and penis. ### The Female Reproductive System The human female reproductive system consists of ovaries, oviducts, uterus, and vagina. ## Session - 3: Fertilisation & the Development of the Embryo ### Objectives - To understand the process of fertilization. - To gain an understanding of how a baby grows in the womb. ### Before You Start #### You Should Know Sperm and the egg are involved in the process of fertilization. The sperm meets the egg in the oviduct. #### Check-in - What is a zygote? - What happens to the zygote after fertilization? ### Fertilization The sperms produced in the testes are introduced into the woman's body into the vagina, through the penis. The sperm cells then travel through the vagina, cervix, and uterus to reach the oviduct. If at the same time, the egg released from any one of the ovaries, also reaches the oviduct, the sperm meets the egg, and there is fertilization. Only one sperm can enter the egg. The fusion of the sperm into the egg is called fertilization. During fertilization, the nucleus of the sperm fuses with the nucleus of the egg cell to form a single nucleus. The fertilized egg is now called a zygote. ### Fertilization which takes place inside the female body is called internal fertilization. Internal fertilization occurs in many animals including humans, cows, dogs, and hens. In many animals, fertilization takes place outside the body of the female. This is called external fertilization. This type of fertilization is commonly seen in frogs, fishes, and starfishes. In frogs, during the spring or the rainy seasons, the male and the female come together in the water. The female frog lays many eggs. The frog's egg is not covered by a shell and is very delicate. A layer of jelly holds the eggs together and provides protection. Then the male frog deposits sperms over them. Each sperm randomly swims towards an egg and fertilises it. This is how external fertilization takes place in the frogs. Despite the fact that these animals lay hundreds of eggs and produce millions of sperms, not all of the eggs are fertilized and grow into new individuals. This is because of the eggs and sperms being exposed to water, wind, and rain. There are also animals in the pond that may eat eggs. To ensure that at least, a few of the eggs and sperms are fertilized, a large number of eggs and sperms must be produced. ## In Vitro Fertilisation (IVF) Some females can't conceive due to blocked oviducts and various other reasons. In such cases, fresh eggs and sperms are collected from the parents by the doctors for a process called in-vitro fertilization. The egg and the sperm collected are fused in the lab. The fertilized egg is allowed to grow in the lab for a week, after which it is implanted into the mother's womb. The baby starts growing and is born like any other baby. Babies born through this technique are called **test-tube babies**. This term can be misleading because the babies don't actually grow in the test tubes. ## Development of the Embryo The fertilized egg repeatedly divides to form a ball of hundreds of cells. The cells then begin to form groups of cells that will develop into different tissues and organs of the body. This is an embryo. The embryo moves from the oviduct into the uterus. The embryo then embeds in the soft and thick lining of the uterus. This is called implantation. When the embryo implants in the uterus, the woman is considered pregnant. The embryo starts developing. The embryo gets food and oxygen from the blood vessels lining the uterus. ## How Does the Embryo of a Hen Develop? Soon after fertilization, the zygote divides repeatedly and travels down the oviduct. As it travels down, many protective layers are formed around it. The hard shell that you see in a hen's egg is one such protective layer. After the hard shell is formed around the developing embryo, the hen finally lays the egg. The embryo takes about 3 weeks to develop into a chick. You must have seen the hen sitting on the eggs to provide sufficient warmth. Did you know that development of the chick takes place inside the egg shell during this period? After the chick is completely developed, it breaks open the egg shell and hatches out. ## In animals which undergo external fertilization, the development of the embryo takes place outside the female body. The embryos continue to grow within their egg coverings. After the embryos develop, the eggs hatch. You must have seen numerous tadpoles swimming in ponds and streams. Here's an activity for you! ## Session - 4: Viviparous & Oviparous Animals ### Objectives - To understand the terms viviparous and oviparous. - To know the difference between viviparous and oviparous animals. ### Before You Start #### You Should Know Some animals like cows give birth to a young one, whereas birds lay eggs, out of which hatches the young ones. #### Check-in Why do some animals give birth, whereas others lay eggs? ### Viviparous and Oviparous Animals Humans, cats, dogs, and kangaroos give birth to their young ones. The animals which give birth to young ones are called viviparous animals. In viviparous animals, the young ones develop in the uterus of the mother. When the foetus is fully developed, the mother gives birth to the baby. For example, the babies you see in your families are born this way. All mammals are viviparous animals. There are some animals which lay eggs, which develop into young ones. The animals which lay eggs, from which the young ones hatch out are called oviparous animals. Birds and reptiles are some of the oviparous animals. You might have seen a hen laying eggs. The young one develops inside the egg, and when the development is complete, the young one hatches out from the egg. Have you observed in your nearby parks, the nests of crows, sparrows, or the mynahs? The birds lay their eggs, incubate the eggs by sitting on them and when the development is complete, the young ones break the shells and come out! ## Metamorphosis in Frogs When the fertilized egg of a frog hatches, an immature young one called a tadpole is seen. The tadpole develops gradually and undergoes many drastic changes before it becomes an adult frog. ## Session - 5: Asexual Reproduction ### Objectives - To understand how asexual reproduction occurs in some animals. - To know the types of asexual reproduction. ### Before You Start #### You Should Know Asexual reproduction is the process of creating new organisms from a single parent without the use of sex cells. #### Check-in How is asexual reproduction different from sexual reproduction? So far we have learnt that reproduction in human beings and some other familiar animals takes place by the process called sexual reproduction. We will now study the reproduction in very small animals like amoeba and hydra. Amoeba and hydra are tiny animals which reproduce by the process of asexual reproduction. Asexual reproduction is the production of a new organism from a single parent without the involvement of sex cells (or gametes). The new organism produced by asexual reproduction is exactly identical to the parent. The two most common methods of asexual reproduction in animals are binary fission and budding. ### Binary Fission Binary fission is commonly seen in animals like amoeba and euglena. The parent organism splits into two new organisms and each grows to become a new individual. When the amoeba has reached a maximum size of the growth, the nucleus lengthens and divides into two. Then the cytoplasm also divides into two parts, one around each nucleus. In this way, one parent amoeba becomes two smaller amoebae. It takes about an hour for the amoeba to divide. Just like an amoeba, paramecium also divides by binary fission. ### Budding In budding, there is a small outgrowth from the parent's body, which then detaches and becomes a new individual. Budding is commonly seen in hydra, sea anemones, sponges, and corals. ### Cloning Cloning is the process of creating an exact replica of a cell, any other living component, or an entire organism. Ian Wilmut and his colleagues at the Roslin Institute in Edinburgh completed the first successful cloning of an animal. They successfully cloned a sheep named Dolly. Dolly was born on 5th July 1996 and was the first mammal to be cloned. ### Word Help - **Binary fission**: Binary fission is one of the types of asexual reproduction, where the parent body splits into two and each grows on to become a new individual. - **Budding**: Budding is a type of asexual reproduction, where there is an outgrowth from the parent's body, which when grown sufficiently detaches from the parent's body and grows on to become a new individual. - **Cloning**: Cloning is the production of an exact copy of a cell, any other living part, or a complete organism.