HOW DO ORGANISMS REPRODUCE?

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1 HOW DO ORGANISMS REPRODUCE? Points to remember:- 1. Reproduction is essential for continuity of living organisms. 2. It involves creation of a DNA copy along with the formation of additional cellular apparatus during cell division. 3. Basically it is of two types Asexual and sexual. Some plants like Rose and Banana are prolifrated by ve getative propagation. 4. There are examples of asexual reproduction where new generation arises from a single cell or single individual as in fission, fragmentation, regeneration, budding, spore formation. 5. Sexual reproduction involves two individuals to produce off spring. 6. Variation occurs due to DNA copying mechanism and sexual reproduction. 7. Reproduction in flowering plants involve transfer of pollen grains from anther to stigma pollination. Gametes fertilize to form zygote. 8. Changes occur in boys and girls at puberty, beard and moustache in boys and growth in breast region in girls apart from other changes. These changes indicate sexual maturation and biological preparedness for reproduction. 9. Sexual reproduction takes place by fusion of both male and female gametes resulting in the formation of zygote which gives rise to offspring. 10. Awareness regarding family planning and sex related communicable diseases (STDs) help individual to maintain normal reproductive health. 11. Condoms, oral pills, Copper-T are some of the contraceptives to avoid pregnancy. NOTES Reproduction is the process by which living organisms produce new individuals similar to themselves. Reproduction ensured continuity of life on earth. Reproduction - A bridge to hereditary transmission. It involves continuation of characters from the parents to daughter cells by Copying of DNA (Deoxyribose Nucleic Acid) molecules present in the chromosomes of the cell. Copying of DNAs is also not a foolproof exercise, even minute changes bring about Variation in the blue print of the offspring s. The useful variations are retained while the harmful one does not go beyond. Actually variations help the species to withstand drastic environmental changes, thus save the species from becoming extinct and promotes its survival for a longer time. This inbuilt tendency of variation is the "fuel" for Evolution.

2 Asexual Reproduction is extremely useful as a mean of rapid multiplication. It is common in lower plants and animals. ASEXUAL REPRODUCTION 1. A single parent is involved 2. Gametes not formed 3. Progeny is Identical to parent SEXUAL REPRODUCTION 1. Both Parents involved 2. Gametes are formed 3. Progeny is only genetically DIFFERENT FORM OF ASEXUAL REPRODUCTION. eg. Fission in Amoeba similar to the parent. 1. FISSION: the parent cell divides/splits into two daughter cell-binary Fission; splits into many cells-multiple Fission 2. BUDDING: A new organism is produced as an outgrowth of the parent body part. 3. SPORE FORMATION: Spores are small, bulb like structure develops at the top of the erect hyphae of the Fungus plant, released into the air and germinate, into new individuals after landing into food or soil.

3 4. FRAGMENTATION: It is the accidental process when the broken pieces of an organism (fragments) grows into a complete organism. eg. Fragmentation in spirogyra 5. REGENERATION: When the simple animals like Hydra Planaria develop a new individual from their broken older part it is known as regeneration. It is carried out by specialized cells which grow large numbers of cells. VEGETATIVE PROPAGATION: A mode of reproduction in which part like the stem, root, leaves develop into new plant under favorable conditions. Benefits 1. Plants can bear flowers, fruits earlier than those produced from seeds. 2. Growing Banana, orange, rose, jasmine that have lost the capacity to produce seeds. 3. Genetically similarity is maintained in the plants. e.g. Sugarcane, rose, grapes by layering or grafting. Artificial Vegetative Propagation: Man has used artificial vegetative propagation to grow many plants. This has enabled farmers and horticulturists to grow many plants in shorter duration and has helped them to earn more profit. Artificial vegetative propagation has also helped in developing many new varieties of plants. Stem cutting, layering and grafting are the preferred means of artificial vegetative propagation. Advantages of Asexual Reproduction: The organism does not have to depend on another organism for carrying out reproduction; because a single parent is needed. It takes less time than sexual reproduction and hence more number of offspring can be produced in shorter time.

4 The offspring are exact clones of their parent. Desirable characteristics can be easily incorporated into plants with artificial vegetative propagation. Disadvantages of Asexual Reproduction: As a single parent is involved, so there is negligible chance of variation. In most of the cases in simple organisms, the parent generation ceases to exist after asexual reproduction. Asexual reproduction cannot give rise to biodiversity which is important for a healthy ecosystem. Test Your Knowledge: 1. Amoeba usually reproduces which type of asexual reproduction? Answer: Binary Fission 2. Name a fungus which reproduces by spore formation. Answer: Rhizopus 3. Name an animal which reproduces by regeneration. Answer: Planaria SEXUAL REPRODUCTION When reproduction takes place as a result of fusion between two gametes, one from each parent, it is called sexual reproduction. This process of fusion between two gametes is called fertilization. ametes is called fertilization. The formation of gametes involves exchange of chromosomal (genetic) fragments between homologous chromosomes causing genetic recombination which leads to variation. SEXUAL REPRODUCTION IN PLANTS It occurs mostly in flowering plants. In fact flowers are the reproductive organ of plants.

5 Both male and female reproductive part i.e., stamen & carpel present. Eg. Hibiscus, mustard Either male or female Reproductive part is present. Eg. Papaya, Watermelon A typical flower consists of four main whorls namely calyx (sepals), Corolla (Petals), Androecium (Stamens) and Gynoecium (Carpels). Pollen grains of a flower transfer to stigma of the carpel of the same flower (Self-Pollination) or to the carpel of another flower (Cross-Pollination). This transfer of pollens is achieved by agent like wind, water or animals. After Pollination, the pollen grains reach to the egg cell in the form of a pollen tube.

6 FERTILIZATION: The fusion between the pollen grain and female egg cell. It occurs inside the ovary. Zygote is produced in this process. Zygote divides several times to form an embryo within the ovule. The ovule develops a tough coat and is converted into a seed. Ovary grows rapidly and ripens to forms a fruit, while the seed contains the future plant or embryo which develops into a seedling under suitable condition. This process is known as Germination.

7 REPRODUCTION IN HUMAN BEINGS Humans use a Sexual Mode of reproduction. It needs sexual maturation which includes creation of the germ cells i.e., egg (ova) in the female and sperm in the male partner & this period of sexual maturation is called Puberty. Human beings have a well developed male and female reproductive system. MALE REPRODUCTIVE SYSTEM The formation of male germ cell (sperms) takes place in the testes (male reproductive organ) Actually a pair of testes is located inside scrotum situated outside the abdominal cavity. It is meant to keep relatively a low temperature needed for the production of sperms by testes. Moreover testes release a male sex hormone called testosterone whose function is to: 1. Regulate the production of sperm 2. Brings about changes in appearance seen in boys at the time of puberty. Figure:- Male reproductive system (i) Side view (ii) Front view The sperms along with the secretion of prostate gland and seminal vesicle together constitute semen, which is released and made to enter into the female genital tract during Copulation. FEMALE REPRODUCTIVE SYSTEM The female germ cells or eggs are made in the ovaries, a pair of which is located in both side of abdomen. When a girl is born, the ovaries already contain thousands of immature eggs. At the puberty, some of these Eggs start maturing. One egg is produced every month by one of the ovaries. The Egg is carried from the ovary to the womb through a fallopian tube. These two fallopian tube unite into an elastic bag like structure known as Uterus. The Uterus opens into the vagina through the cervix.

8 Figure:- Female reproductive system Fertilization occurs in the fallopian tube of female genital tract. The fertilized egg also called zygote (2n) gets implanted in the lining of the Uterus, and start dividing. Actually uterus is richly supplied with blood to nourish the growing embryo. If zygote is not formed, the inner wall of uterus breaks which causes bleeding through vagina. This process is called MENSTRUATION. It occurs at a regular interval of 28 days. The Embryo gets nutrition from the mother's blood with the help of a special tissue called PLACENTA. It provides a large surface area for glucose and oxygen to pass from the mother to the embryo. Similarly the wastes from developing embryo are removed to mother's blood through placenta. The child is born as a result of rhythmic contractions of the muscles in the uterus. after Nine months (36 weeks) of development inside mother's womb. It is also called Gestation Period. The sexual cycle in a woman continues up to the age of 45 to 50 years. After that the ovary does not release egg. This stage is called Menopause. It a also marks the end of menstruation in the woman. REPRODUCTIVE HEALTH Reproductive Health means a total well-being in all aspects of reproductive, ie., physical emotional, social and behavioural. Contraception: It is the avoidance of pregnancy. It can be achieved by Methods of contraception.

9 Healthy society needs a balanced sex ratio that can be achieved by educating the people to avoid malpractices like female foeticide & pre-natal sex determination. STDs are communicated during unsafe sexual contact.

10 SUMMARY Reproduction in Human Beings Male Reproductive System: The male reproductive system in human beings is composed of following parts:- a. Testis:- There is a pair of testes; which lie in a skin pouch; called scrotum. Scrotum is suspended outside the body; below the abdominal cavity. This helps in maintaining the temperature of testes below the body temperature. This is necessary for optimum sperm production. Testis primarily serves the function of sperm production. Sperms are the male gametes. Apart from that, testis also produces testosterone. Testosterone is also called the male hormone, as it is responsible for developing certain secondary sexual characters in boys. b. Vas deferens:- Vas deferens is the tube which carries sperms to the seminal vesicle. c. Seminal Vesicle:- This is the place where sperms are stored. Secretions from the seminal vesicle and prostate gland add up to make the semen. d. Penis:- It is a muscular organ which serves the genitor-urinary functions. The urethra works as the common passage for urine as well as for sperms. Female Reproductive System:- The female reproductive system in human beings is composed of following parts: a. Uterus:- This is pear-shaped hollow muscular organ. Uterus is the place where the embryo gets implanted and develops into a newborn baby. The wall of the uterus provides safety and nutrition to the growing foetus. b. Fallopian Tubes:- One fallopian tube comes out from each side at the top of the uterus. The fallopian tubes end in finger-like structures; called flimbriae. Fertilization happens in the fallopian tube. c. Ovary:- There are two ovaries; one near each fallopian tube. Ovary produces the eggs or the female gametes. All the eggs are produces by the ovary when the female child is still in the womb. One egg matures in each ovulation cycle and is released from the ovary. The egg is caught by the flimbriae and transferred to the fallopian tube. d. Vagina:- The cervix (mouth of the uterus) opens into the vagina. Vagina is a muscular tube-like organs; which serves as the passage for the sperms and also as the canal during the child birth. Puberty:- Human beings are complex animals and hence there is a distinct phase in their life cycle which marks the onset and attainment of sexual maturity. This period is called puberty. It usually starts at around years of age in girls and at around years of age in boys. It usually ends at around 18th year of age in girls and at around 19th year of age in boys. Since the years during puberty end in teens ; hence this phase is also called teenage. Sexual Dimorphism:- The physical dissimilarities in the male and female of a species which give them different appearances is called sexual dimorphism. Secondary Sexual Characters:- Features which highlight sexual dimorphism are called secondary sexual characters. Changes in Boys during Puberty:- The boys suddenly grow in height dramatically. Voice becomes deep and the Adam s apple becomes prominent. Shoulders become broad and body becomes muscular. Facial hairs begin to grow. Hairs also grow under the armpit and in the pubic region. Changes in Girls during Puberty:- The voice becomes thin. Shoulders and hip become rounded. Breasts get enlarged. Hairs grow under the armpit and in the pubic region. Menstruation:- Menstruation is a trait which is unique to humans and some primates. During each ovulation cycle, the uterus prepares itself in anticipation of a possible pregnancy. The uterine wall develops an additional lining. When the egg is not fertilized, it gets disintegrated and so does the additional lining in the uterine wall. The fragments of disintegrated tissues are shed; along with blood. This is observed in the form of bleeding through the vagina which can last from 3 to 7 days. The whole sequence of events during an ovulation cycle is called menstrual cycle. The bleeding which occurs for few days is called menstruation. The first menstrual flow is called menarche and the last menstrual flow (which happens in the late 40s) is called menopause.

11 Test Your Knowledge:- 1. Which hormone is also known as the male hormone? Answer:- Testosterone 2. What is the name of the structure which provides nutrition to the developing foetus? Answer: Placenta Reproductive Health Human beings are different than other animals because they have the power of thinking. They have to obey certain moral values and need to behave sensibly in most of the aspects of life. Beginning of puberty does not mean that a person is psychologically ready for the process of reproduction. For a human being, reproduction involves more than just producing an offspring. As any act of sex has the potential of fertilization, so taking care of contraception becomes important. Moreover, the act of sex also has the potential of creating many sexually transmitted diseases. Examples of STDs are; gonorrhea, Herpes, syphilis, AIDS, Hepatitis B. AIDS and Hepatitis B are incurable till date. Even the curable STDs are potential dangerous; not only physically but also psychologically. Reproductive health involves preventing the chances of STDs and preventing unwanted children. Reproductive health means a couple should be able to enjoy the reproductive phase of its life; without taking the burden of gigantic family. VERY SHORT ANSWER TYPE QUESTIONS (1mark each) 1. Define reproduction. Ans It is the process of producing new organism of the same species by existing organisms of a species. 2. Define fertilization. Ans- It is defined as the fusion of a male gamete (sperm) with a female gamete (ova) to form a zygote during sexual reproduction. 3. Name two type of reproduction. Ans-Two main type of reproductions is asexual reproduction and sexual reproduction. 4. The anther contains: a...sepal b. ovules c. carpel d.. Pollen grains Ans Pollen grains 5. What method will you use for growing jasmine and rose plant? Ans artificial mode of vegetative reproduction-layering and grafting are use for growing jasmine and rose plant. 1. Define menstruation. Ans-The breakdown and removal of inner thick and soft lining of uterus along with blood vessels in the form of veginal bleeding is called menstrual flow or menstruation. 7. Write the name of male and female reproductive part of a flower. Ans-Male reproductive part is stamen, which consists of filament and anther. Female reproductive part is carpel, which consists of ovary, style and stigma. 8. Where does the fertilization takes place in human female? Ans in oviduct. 9. Why do testes in mammals descend in scrotum? Ans-The location of the scrotum regulates the temperature of the testes because sperm formation requires a lower temperature than the body temperature. 10. Name the type of fission carried out by Amoeba. Ans-Amoeba reproduces by binary fission in which one cell divides into two daughter cells. 11.Name two sexually transmitted diseases. Ans-Gonorrhea and syphilis. 12. Name the male and female gonads and what are the products they produce? Ans-Male gonads-testes, Products-Hormone testosterone which stimulates the secretion of sperm from testes. Female gonads ovaries, Products-hormones estrogen and progesterone, which stimulates the secretion of eggs. 13.-Where does fertilization takes place in human female? Ans- In fallopian tube (oviduct). 14. What is vegetative propagation? Ans-- The development of new plants from parts such as roots, stem and leaves, of the plant is called vegetative propagation.

12 15. Expand AIDS, Ans- Acquired immune deficiency syndrome. 16. Write the full form of IUCD. Ans-- Intra Uterine Contraceptive Device. 17. What is syngamy? Ans The fusion of one male gamete with an egg to form zygote is called syngamy. 18. What is advantage of fruit formation in plant? Ans Fruit formation helps in easy dispersal of seed. 19. What is ovulation? Ans The release of ovum or the egg from the ovary is called ovulation. 20. What is menopause? Ans-The permanent stoppage of menstruation at age of years is called menopause. 21. Which part of human female reproduction system is called birth canal and the womb? Ans Vagina is called the birth canal and the uterus is called the womb. 22. Define gestation period. What is the gestation period in human? Ans The time period from the development of foetus inside the uterus till birth is called gestation period. In humans, the gestation period lasts for 9 months or 40 week or 280 days. SHORT ANSWER TYPE QUESTIONS (Each of 2 marks) 1. What is the importation of DNA copying in reproduction? Ans-DNA copying helps to pass on the parental body features to offspring s. It produces variations, which are useful for the survival of species over time. 2. Why is variation beneficial to the species but not necessarily for the individual? Ans-Organisms are normally adopted to live in a particular kind of niche. In case of alternation in the ecological conditions of that niche, the organisms would not be able to survive. Only the variants the organisms resistant to changes would survive and grow further. Thus variation is beneficial to the species not necessarily for the individual. 3. How does binary fission differ from multiple fission? Ans-Binary fissions results in the formation of two equally sized daughter cells, whereas multiple fission results in the formation of many daughter cells. 4. How will an organism be benefited if it reproduces through spores? Ans-An organism if it reproduces through spores in the following ways: A. Spores are formed in large number. B.Spores has an outer thick wall that protects them in adverse conditions until they come in contact with another moist surface and begin to grow. 5. Can you think of reasons why more complex organisms cannot give rise to new individuals through regeneration? Ans-More complex organisms cannot give rise to new individuals through regeneration because: i. There body is highly complicated. ii. There are specific organ for specific functions. iii. There is a labour division in the body of complex organisms. iv. Regeneration is carried out by specialized cells which are not present in complex organisms. 6. Why vegetative reproduction is practiced for growing some type of plants? Ans-Vegetative reproduction is practiced in some types of plants due the following reasons: 1. The plants which do not produce viable seeds are propagated by vegetative propagation such as banana, orange and rose. 2 Plants raised by vegetative propagation bear flower and fruit earlier than those produce from seeds. 3. Seedless fruits are produced by vegetative propagation. 7. Why is DNA copying an essential part of the process of reproduction? Ans- a) DNA copying provides cellular apparatus in the daughter cells. b) DNA copying is essential for obtaining exact body design.

13 c) It is essential for inheritance of features from parents to offspring. 8. What are the changes seen in girl s at the time of puberty? Ans-Various changes take place in girl s body at the time of puberty: a) Thick hair growth in the arm pit and genital area. b) Oily skin and appearance of pimples c) Breast size begins to increase d) Girls begin to menstruate etc. 9.. What is the role of the seminal vesicles and the prostate gland? Ans The secretion of seminal vesicles activates and nourishes the sperms whereas the secretion of prostate gland contributes the mortality and fertility of sperms. 10. How is the process of pollination different from fertilization? Ans-Pollination is the process of transfer of pollen grains from anther to stigma whereas fertilization is the process of fusion of male gamete with a female gamete to form zygote. 11. How does the embryo get nourishment inside the mother s body? Ans-The embryo gets nourishment inside the mother s body through placenta. This tissue contains villi on the embryo s side and is surrounded by blood from the mother s side. Substances like glucose and oxygen pass from the mother s blood to the embryo through villi. 12. If a woman is using copper Twill it help in protecting her from sexually transmitted diseases? Ans-No, because copper-t helps in preventing pregnancy, but not provide protection against sexually transmitted diseases. 13. Show by a series of labeled diagram, the manner in which reproduction in Hydra. Ans-Hydra reproduces by budding using the regenerative cells. A bud develops as a outgrowth in hydra due to repeated cell division of specific site, when full mature, the bud detaches from the parent s body and develop into new individuals. 14. Describe regeneration. Fig- Ans-It is ability of a fully differentiate organisms to give rise to new individual from its body parts. For example-hydra and Planaria. If Hydra is cut into two or more pieces grow into new and complete Hydra.This is known as regeneration. 15. Define the terms unisexual and bisexual flowers by giving one example of each. Ans-Unisexual flower means flower which contain only one sex organs either stamen or carpel but not both.expapaya, watermelon. Bisexual flower means flower which contain both stamen and carpels. Ex- hibiscus. 16. Leaves of the bryophyllum fallen on the ground produce new plants whereas the leaves of rose do not. Why? Ans-Leaf of bryophyllum show vegetative propagation in plants where a part of the body becomes detached and develop into a new supporting plant..here leaves of bryophyllum having plantlets along the margine of the leaf, while this structure is absent in rose plant.

14 17. Why does menstruation occur? Ans. The removal of the inner, thick and soft lining of the uterus along with its blood vessels as well as blood in the form of vaginal bleeding is called menstruation. In humans after a girl attains puberty ovaries start producing mature ovum every month and also uterus lining gets thickened to receive zygote. When the uterus does not receive any zygote then menstruation occurs to excrete lining of uterus and degenerating ovum. 18. What are the different methods of contraception? Ans. The different methods of controlling the child birth are (1) Hormonal methods: Various kinds of pills containing hormones which prevent the release of egg from the ovary, without interfering with other phases of menstrual cycle, are taken orally. (2) Barrier method: These are the physical and chemical barriers which prevent the sperms meeting the egg. Physical devices such as condoms, diaphragms and cervical caps are used. (3) Intrauterine Devices: Commonly called as I.U.Ds, they are the devices made of plastics and come in different shapes. The most commonly among these is copper- T. These devices are placed inside the uterine cavity and permanently kept there. It prevents the implantation in the uterus. 4) Surgical methods. The surgical methods are safe and permanent. (i) Vasectomy. In this operation, a small piece of vas deferens is cut and removed and the two ends of the cut vas deferens are tied. (ii) Tubectomy. In this operation, fallopian tubes are cut, tied with nylon thread to close the passage, which prevents the passage of eggs. 19. How are the modes of reproduction different in unicellular and multicellular organisms? Ans. Unicellular organisms contain only one cell so they reproduce by asexual reproduction. Example: budding, binary and multiple-fission are some of the asexual methods. Multicellular organisms which have complex body designs (have organ systems) ex. Humans, animals, plants reproduce sexually. 20. How does reproduction help in providing stability to populations of species? Ans. Reproduction is the process through which an organism produces new organism of its own kind. It is necessary because in a population organisms die due to old age or disease thus it keeps the number of organisms in a population constant and provides stability to a population.