Viviparous and Oviparous Animals PDF

## Viviparous and Oviparous Animals Organisms can be classified on the basis of their mode of bearing young ones. Animals are classified into viviparous and oviparous based on whether the zygote develops inside or outside the body respectively. ### Viviparous Animals Animals which give birth to yo...

## Viviparous and Oviparous Animals Organisms can be classified on the basis of their mode of bearing young ones. Animals are classified into viviparous and oviparous based on whether the zygote develops inside or outside the body respectively. ### Viviparous Animals Animals which give birth to young ones are called viviparous animals. Cats, dogs, rats, cows, deer, and humans are examples of viviparous animals. In these animals complete development of the fertilized egg or zygote into a young one takes place inside the mother's body. The mother then gives birth directly to the young ones. ### Oviparous Animals Animals that lay eggs are called oviparous animals. Animals like fish (e.g., Indian salmon, mackerel, and rohu), amphibians (e.g., frog and toad), birds (e.g., parrot, eagle, ostrich, and crow), insects (e.g., grasshopper, cockroach, and butterfly), spiders and reptiles (e.g., crocodile, turtle, and snake) are examples of oviparous animals. In these animals, fertilization can take place internally or externally, while embryo development always occurs outside the mother's body. Eggs are laid by the females and the development of the young ones takes place inside the eggs. When the development is complete the young ones hatch out of the eggs. Animals like hens sit on the eggs to provide them warmth till the chicks are fully developed. This is known as incubation. ### Animals from Young Ones to Adults The young ones of each animal species continue to grow and develop into adults. #### Resemblance In some animals, the newly born young ones resemble adults. Mammals including humans and birds are animal species in which the young ones look similar to adults. #### Transformation On the other hand, the young ones of some animals look very different from adults. Silkworms, butterflies, and frogs are animal species in which young ones look very different from adults. The young ones of these animals undergo a series of changes to mature into adults. The series of changes in the form or structure of an animal during its life cycle from the embryo stage to the adult stage is known as metamorphosis. #### The Life Cycle of a Frog A frog begins its life cycle at the egg stage. 1. **Egg Stage:** The embryo present inside the frog egg develops into a tadpole which hatches out of the egg. 2. **Tadpole Stage:** A tadpole differs from the adult frog in structure and appearance. - Tadpoles have tails to swim and use gills to breathe in water. - Tadpoles can live only in water. 3. **Metamorphosis:** As a tadpole matures, it loses its tail and develops limbs and lungs. 4. **Young Frog:** A tadpole transforms into a young frog which matures into an adult frog. ### Study Tip * **Inside Oviduct** * Ovum * Fertilization * Zygote * **Inside Uterus** * Embryo * Foetus * Baby ### Did You Know There are three types of honey bees in a bee colony: The queen, drones (male bees), and worker bees. Queen bee and worker bees develop from the fertilized eggs. However, the drones are produced by a process called parthenogenesis. It is a form of reproduction in which the ovum develops into a new individual without fertilization. ### Enrichment Most animals have separate sexes. For example, the male reproductive system is present in human males while the female reproductive system is present in human females. Some exceptional organisms have both male and female reproductive organs within a single organism. Such organisms are called hermaphrodites. Even though the gametes come from the same individual, their mode of reproduction is still considered sexual reproduction, as two gametes are involved. Snails and earthworms are hermaphrodite organisms. ### In Vitro Fertilization (IVF) * In vitro fertilization is a technique used to assist in reproduction. * In certain cases, due to problems in the oviduct, fertilization cannot take place naturally. In these cases, in vitro fertilization is helpful. * An egg of the female and a sperm of the male are fused under controlled conditions in a laboratory. * The fertilized egg or zygote, which is formed is grown for about a week in an external medium, outside the mother's body. * After a week, the zygote is implanted into the uterus of the mother. * Complete development of the baby takes place in the mother's body and once the development is complete, the mother gives birth to the baby. * Babies who are born using IVF are often called 'test tube' babies. ### Fertilization in Humans * Fertilization takes place in the oviducts or fallopian tubes of the female. * One of the sperms may fuse with the ovum, and the nucleus of the sperm fuses with the nucleus of the ovum in the fallopian tubes to form a single-celled zygote. * This process of fusion of a male gamete with a female gamete to produce a single-celled zygote is called fertilization. #### Stages of Embryonic Development 1. **Zygote Formation:** Since a zygote is formed by fusion of the ovum from the mother and sperm cell from the father, therefore, the new individual which develops from the zygote will inherit characteristics from both the parents. 2. **Embryo Formation:** The zygote formed in the fallopian tube divides and re-divides to form a ball of cells called embryo. 3. **Implantation:** Embryo moves into the uterus and attaches itself to the inner wall of the uterus for further development. The process by which an embryo attaches itself to the inner uterine wall is known as implantation. Implantation marks the beginning of pregnancy. 4. **Development:** After implantation, an embryo continues to grow and develop in the uterus. The cells of the embryo specialise and form the tissues, organs, and organ systems. The process of specialisation of cells to form organ and organ systems of the body is called cell differentiation. When all body parts of an embryo can be identified, it is called a foetus. It takes about 8 weeks for an embryo to develop into a foetus 5. **Foetal Development:** The foetus continues its development within the womb of the mother. The time period from the fertilization of the egg till the birth of the baby is known as the gestation period. The average length of the gestation period in humans is about 280 days or 40 weeks. 6. **Birth:** At the end of the gestation period, the mother gives birth to a baby. The contractions of the mother's uterine muscles aid in the delivery of the baby ### The Sperm * Each sperm is a single cell with three basic parts: head, middle piece, and tail. * The head of the sperm secretes enzymes that can easily digest the jelly coat of an ovum and enter it to fuse with the nucleus of the ovum. * The middle piece of the sperm provides energy to the tail to move. * The tail enables the sperm to move quickly toward the female gamete or egg (ovum). ### Fertilization * The process in which the male and the female gametes meet and fuse together to form a zygote is known as fertilization or syngamy. * Depending on the species, fertilization can occur either outside the body known as external fertilization or inside the body known as internal fertilization. * For example, in fish and frogs, fertilization takes place outside the body. The female releases multiple eggs in the water and at the same time, the male releases sperms in the water. * The sperms swim through the water and on reaching an egg, one of the sperms fertilizes the egg. Multiple sperms can fertilize multiple eggs. * The fertilized eggs remain in water and develop into new individuals. This type of fertilization that takes place outside an organism's body is known as external fertilization. A large number of eggs are fertilized by this method because most of the fertilized eggs get washed away or are eaten up by predators. A large number of eggs ensures the survival of some offspring. * When fertilization takes place inside the animal's body, it is known as **internal fertilization**. * Internal fertilization happens in most terrestrial animals such as insects, reptiles, birds, and mammals. ### Parts and Functions of the Female Reproductive System: | Part | Function | |---|---| | **Oviducts or Fallopian Tubes** | - The funnel-shaped end of the fallopian tubes picks up the egg or ovum released by the ovary. The released egg moves along the fallopian tube towards the uterus. - Fertilization of the ovum by the sperm takes place in the fallopian tube and a zygote is formed. - The zygote develops into an embryo. - If the egg or ovum is not fertilized, it is discharged from the body along with blood and the lining of the uterine wall by a process known as menstruation. | | **Uterus** | - Development of the embryo takes place in the uterus. - Embryo develops into a foetus. - Foetus grows into a baby inside the uterus. | | **Vagina** | - Serves as the entrance of sperms into the female body. - After entering the female body through the vagina, sperms travel (swim) up and enter the uterus through the cervix. - After traversing the uterus they enter the fallopian tubes. - It also forms a part of the birth canal as it stretches to allow the delivery of the baby. | - Unlike males where only one duct (urethra) is used for both urinary and seminal discharge, females have separate urinary and vaginal openings. ### Gametes in Human Beings * At birth, a female already has thousands of partly developed eggs inside her ovaries. - When she reaches puberty, these eggs start to mature inside the ovaries by the process of ovulation. - Generally, one egg (ovum) develops at a time. - Ovulation happens once in every four weeks. * The ovum is surrounded by a coat of jelly that protects the contents of the ovum and prevents the entry of more than one sperm. - In human males, sperms are made continuously once puberty is reached. - Sperms are much smaller than eggs and are produced in much larger numbers. #### Location of Various Female Reproductive System Parts * **Ovaries** are two small oval-shaped organs. They are located in the abdominal cavity on each side of the uterus. * **Oviducts or fallopian tubes** extend from the edge of each ovary to the uterus. The end of each fallopian tube is funnel-shaped. The other end opens in the uterus. * The **uterus** is a hollow, pear-shaped organ that is located between the urinary bladder and the rectum. The uterus is also known as the womb. * The **cervix** is the lower narrow part of the uterus opening into the vagina. * The **vagina** is a short narrow muscular tube that connects the uterus to the exterior of the body. #### Functions of the Female Reproductive System | Part | Function | |---|---| | **Ovaries** | - Produce eggs or ova (the female gamete). - Once the female reaches sexual maturity or puberty, a single matured egg (or ovum) is released into the oviduct by one of the ovaries every month. - The process of release of mature ovum by the ovaries is called ovulation. It happens once in four weeks. - Ovary produces female sex hormones - oestrogen and progesterone. These hormones regulate the changes observed in the female body, such as breast development and widening of hips. > Oestrogen ensures that only one egg matures every month. > Both hormones help to maintain the uterus lining for implantation of embryo. | | **Uterus** | | | **Vagina** | | ### Gametes in Humans * At birth, a female already has thousands of partly developed eggs inside her ovaries. * When she reaches puberty, these eggs start to mature inside the ovaries by the process of ovulation. - Generally, one egg (ovum) develops at a time. - Ovulation happens once in every four weeks. * The ovum is surrounded by a coat of jelly that protects the contents of the ovum and prevents the entry of more than one sperm. * In human males, sperms are made continuously once puberty is reached. ### Parts and Functions of the Male Reproductive System: | Part | Function | |---|---| | **Testes** | - Produce sperms or the male gametes. - Also produces the male sex hormone testosterone. This hormone is responsible for the development of secondary sexual characteristics such as a beard, a muscular body, and hoarseness of voice in males. | | **Epididymis** | - Immature sperms produced by the testes move into the epididymis. - Epididymis stores these sperms. - Sperms mature in the epididymis and then move to the sperm ducts. | | **Sperm ducts** | - Help to transport sperms from the epididymis to the urethra in the penis. | | **Seminal vesicles** | - Secrete seminal fluid. - This fluid provides nourishment to the sperm cells helping them to remain motile. | | **Prostate gland** | - Alkaline secretion of the prostate gland provides: > a protective environment for the sperms, > keeps them alive, and > helps them to swim efficiently. | | **Cowper's glands** | - White viscous and alkaline secretion of these glands acts as a lubricant for the penis. - [Semen is therefore, a mixture of sperms and secretions of seminal vesicles, prostate gland and Cowper's glands.] | | **Urethra** | - It carries both sperms from the vas deferens and urine from the bladder outside the body. - In males, the urethra is a part of both the reproductive system as well as the urinary system. | | **Penis** | - It contains the urethra hence it helps both in: > the transfer the semen to the female reproductive system, and > urination. | #### Location of Various Male Reproductive System Parts * **Testes (male gonads)** are located within a sac-like structure called scrotum, present just below the penis outside the abdominal cavity. * **Scrotum** is present outside the abdominal cavity as it has to maintain the temperature of the testes slightly lower than the body temperature (2-3 degrees lower). The lowered temperature is necessary for the production of sperms. * **Epididymis** lies on the backside of each testicle. It is a long, tightly coiled tube that is enclosed in a fibrous covering. * **Sperm ducts or vas deferens** are a pair of narrow muscular ducts that connect the testes to the urethra. * **Urethra** is a tube-like structure that passes through the penis and its external opening is located at the tip of the penis. * **Penis** is located above the scrotum. It is one of the external organs of the male reproductive system and it is made up of muscles, spongy tissue and blood vessels. * **Seminal vesicles** are a pair of sac-like glands that open into each sperm duct just before it joins the urethra. * **Prostate gland** is a small walnut-sized gland located below the urinary bladder at the base of the urethra. * **Cowper's glands** are pea-sized glands located just below the prostate gland on the sides of the urethra. * Secretions from the seminal vesicles, prostate gland, and Cowper's glands empty into the spermatic duct. #### Functions of the Male Reproductive System | Part | Function | |---|---| | **Testes** | - Produce sperms or the male gametes. - Also produces the male sex hormone testosterone. This hormone is responsible for the development of secondary sexual characteristics such as a beard, a muscular body, and hoarseness of voice in males. | | **Epididymis** | - Immature sperms produced by the testes move into the epididymis. - Epididymis stores these sperms. - Sperms mature in the epididymis and then move to the sperm ducts. | | **Sperm ducts** | - Help to transport sperms from the epididymis to the urethra in the penis. | | **Seminal vesicles** | - Secrete seminal fluid. - This fluid provides nourishment to the sperm cells helping them to remain motile. | | **Prostate gland** | - Alkaline secretion of the prostate gland provides > a protective environment for the sperms, > keeps them alive, and > helps them to swim efficiently. | | **Cowper's glands**| - White viscous and alkaline secretion of these glands acts as a lubricant for the penis. - [Semen is therefore, a mixture of sperms and secretions of seminal vesicles, prostate gland and Cowper's glands.] | | **Urethra** | - It carries both sperms from the vas deferens and urine from the bladder outside the body. - In males, the urethra is a part of both the reproductive system as well as the urinary system. | | **Penis** | - It contains the urethra hence it helps both in: > the transfer the semen to the female reproductive system, and > urination. | ### Female Reproductive System * The female reproductive system in human beings includes: * a pair of ovaries (main reproductive organ) * a pair of oviducts or fallopian tubes * uterus * vagina ### Modes of Reproduction There are two modes by which animals reproduce: * Asexual reproduction * Sexual reproduction ### Asexual Reproduction * A type of reproduction where offspring are produced from a single parent without the fusion of sex cells is known as asexual reproduction. * In asexual reproduction, the offspring are identical to the parent, both physically as well as genetically. * This type of reproduction takes place in a favourable environment only. * Table 6.1 lists the advantages and disadvantages of asexual reproduction: #### Advantages of Asexual Reproduction * Only one parent is needed. * No gametes (sex cells) are involved. * All characteristics of parents are passed on to the offspring. * Faster process. #### Disadvantages of Asexual Reproduction * Little or no variation in offspring. * For example, If the parent has no resistance to a specific disease, none of the offspring will have resistance to that disease. #### Types of Asexual Reproduction * Binary fission * budding * fragmentation #### Binary Fission * Binary fission involves the division of a parent organism into two identical daughter cells. * At first, the nucleus elongates and divides to form two daughter nuclei. * Then the cytoplasm of the mother cell divides to form two daughter cells. * Each daughter cell has a nucleus and its own cell organelles. * The daughter cells are genetically identical to each other and grow independently into adults that can undergo further binary fission. * This type of reproduction is mostly seen in unicellular organisms like amoeba, paramecium, and euglena which have relatively simple structures and can divide very quickly. #### Budding * In this type of reproduction, small outgrowths or bulges called buds develop on the body of the parent organism due to repeated cell division. * The nucleus of the parent body divides into two, out of which one goes into the bud. * When the buds are fully mature, they separate from the parent body to begin life as independent individuals. * For example, a parent hydra develops a bud due to cell division. * This bud detaches from the parent hydra once it fully matures. * The newly developed offspring or individual is the same as the parent because it has developed from a single parent. * Animals like hydra and flatworms reproduce by budding. * Unicellular fungi like yeast also reproduce by budding. #### Fragmentation * Fragmentation is a type of reproduction in which a new organism develops from parts or fragments of the parent body. * When conditions are ideal, the parent body breaks into two or more fragments and each one develops into a new organism. * The regeneration and development of a new individual depends on the size of the fragment. * If the fragment is large enough it will regenerate and develop into a new individual. * Multicellular organisms like hydra, planaria, starfish, etc., reproduce by fragmentation. * Regeneration is a process in which organisms can regrow a body part that is cut, lost, or broken. For example, if an individual arm of a starfish is cut off or broken, this broken arm can develop into a new starfish. * The parent starfish can grow the arm again, by the process of regeneration.. ### Sexual Reproduction * A type of reproduction where new organisms are formed by the fusion of male and female gametes is called sexual reproduction. * The offspring show variations in their characteristics and are not identical to the parents. * Male and female members of each animal species produce special cells called the male and female gametes, respectively. * Gametes are also called sex cells or reproductive cells. * The female reproductive system of a sexually mature female produces the female gametes called the egg or ovum. * The male reproductive system of a sexually mature male produces the male gametes called the sperms. * The male and the female gametes fuse to form a zygote. * The zygote or fertilized egg inherits one-half of the chromosomes from the mother and the other half from the father. #### Fertilization * The process of fusion of a male gamete with a female gamete to produce a single-celled zygote is called fertilization. * The zygote multiplies and forms a ball of cells called an embryo. * The stage of the embryo in which all the body parts such as hands, legs, eyes etc., can be clearly identified is called a foetus. * When the foetus develops completely, the mother gives birth to a baby. * Humans, cats, bears, dogs, fish, birds, reptiles, etc., reproduce by sexual reproduction. * Table 6.2 lists the advantages and disadvantages of sexual reproduction. ### Advantages of Sexual Reproduction * Variation is seen in offspring. * This increases the chances of survival and continuity of species during unfavourable conditions. * Disease is less likely to affect the population as offspring may have resistance to diseases. ### Disadvantages of Sexual Reproduction * Two parents (gametes) are involved. * Slower process. ### Difference between Asexual and Sexual Reproduction | Criteria | Asexual Reproduction | Sexual Reproduction | |---|---|---| | Number of parents | One parent is needed | Two parents are needed | | Level of genetic similarity | Offspring is genetically similar to the parent | Offspring is genetically different from the parents | | Number of offspring produced | A larger number of offspring are produced. | Usually, a limited number of offspring are produced. | | Time taken to produce offspring | It is a faster process | It is a slower process | ### Misconception * **Myth:** Sexual reproduction is better than asexual reproduction. * **Fact:** All species would reproduce through sexual reproduction if this method of reproduction were clearly superior to asexual reproduction. * Both methods of reproduction, however, are still present in a variety of living organisms, indicating that each type of reproduction has some sort of evolutionary advantage. * For example, sexual reproduction creates variation in offspring but is a slow process. * Asexual reproduction on the other hand takes less time, but limits variation in offspring. ### Reproduction in Human Beings * Human beings reproduce by the sexual method of reproduction. * The production of male and female gametes begins in humans after the male or female reaches the age of sexual maturity or puberty. * The organs that enable a human being to reproduce form the reproductive system of the body. * Fertilisation as well as the development of the baby takes place in the mother's body. #### Male Reproductive System * The male reproductive system in human beings includes: * a pair of testes (main reproductive organ) * ducts (epididymis, sperm ducts or vas deferens and urethra) * accessory reproductive organs (penis, seminal vesicles, prostate gland, and Cowper's glands) #### Activity 6.1 * Observe permanent slides of budding in hydra and yeast. #### Materials Required * permanent slides showing budding in hydra and yeast * compound microscope #### Procedure: 1. Observe the permanent slide of hydra under the compound microscope. 2. Note down the key features observed. 3. Next observe the permanent slide of yeast under the compound microscope. 4. Note down the key features observed. ### Binary Fission * In this type of reproduction, a single-celled organism divides into two identical daughter cells. * The nucleus of the parent cell divides into two. * The cytoplasm of the parent cell then divides. * Examples of organisms that reproduce by binary fission include amoeba and paramecium. ### Activities * **Aim:** Observe permanent slides of budding in hydra and yeast. * **Materials Required:** - Permanent slides showing budding in hydra and yeast - Compound microscope * **Procedure:** 1. Observe the permanent slide of hydra under the compound microscope. 2. Note down the key features observed. 3. Next observe the permanent slide of yeast under the compound microscope. 4. Note down the key features observed. ### Multicellular Organisms * Several multicellular organisms such as hydra, planaria, and starfish reproduce by fragmentation. * If an individual arm of a starfish is cut off or broken, this broken arm can develop into a new starfish. * The parent starfish can grow the arm again, by the process of regeneration.