Chapter 15 : REPRODUCTION IN ORGANISMS

1. What is reproduction? What is the aim (purpose) of reproduction?
   ANS
   
   • Reproduction is the process by which new organisms of the same species are produced by existing living organisms.
   • The aim of reproduction is the continuation of life on earth. It ensures survival of the existing species of organisms and formation of new species from existing ones by the process of evolution.
2. How do organisms create exact copies of themselves?
   ANS
   
   • Organisms of the same species have similar characteristics as regards body design and body function.
   • In the nucleus of the cells of an organism, the information controlling the common characteristics of the species is stored in DNA.
   • This information leads to the synthesis of proteins controlling the characteristics of the species.
   • During reproduction, duplication of DNA takes place and the information is exactly copied. This leads to the formation of new cells with similar characteristics.
   • If the information is changed due to some reason, the characteristics transferred to the progeny change and the body design changes in the progeny.
   • If these changes are compatible, then the cells survive and a progeny with differing characteristics comes into existence.
   • This is called variation and is the essence of evolutionary process.
3. Describe the importance of variation.
   ANS
   
   • Reproduction gives stability of populations of species in an ecosystem by the maintenance of overall body features.
   • This is achieved by consistency of DNA copying during reproduction.
   • However, the niches (ecosystems) keep on changing because the factors affecting the change are not controlled by the organisms.
   • Alteration in temperature, humidity, water level and phenomena like meteorite hits are examples of factors affecting the change.
   • Suppose the population of reproducing organisms is suited to a particular niche and if there is a drastic change in the niche, the population may be wiped out.
   • But if there were some variations present in a few individuals of this population, there would be some chance for them to survive.
   • For example, if there was a population of bacteria living in water with moderate temperature and if the water temperatures were to rise due to global warming, many bacteria would die but a few temperature resistant bacteria would survive and grow further.
   • Thus, variation is useful for the survival of the species.
4. What is the basic difference between asexual reproduction and sexual reproduction?
   ANS
   The basic difference between asexual reproduction and sexual reproduction is that only one parent is required for asexual reproduction, i.e. there is no distinction like male and female whereas sexual reproduction requires two parents, one male and one female.
5. Describe different methods (types) of asexual reproduction.
   ANS
   
   • Fission:
     • This is the simplest method of asexual reproduction in which a unicellular organism (like protozoa, bacteria) divides to form two new organisms.
     • There are two types of fission: (i) Binary fission (ii) Multiple fission.
     • Binary Fission:In binary fission, the nucleus lengthens and divides into teo parts. Then the cytoplasm divides into two parts, one part around each nucleus. This results into two daughter cells which then grow as individual organisms.
       Example: Amoeba, Paramoecium.
       
       
     • Multiple Fission: Under certain circumstances, the nucleus of the cell divides several times within the cell forming many nuclei. Particularly when a unicellular organism forms cyst around the cell during unfavourable conditions, the nucleus divides several times within the cyst forming many smaller daughter nuclei. Each nucleus is then surrounded by a small amount of cytoplasm and a thin membrane. When favourable conditions arrive, the cyst breaks and all those daughter cells are released.Each cell then forms a new organism.
       Example: Plasmodium, Amoeba.
       
       
   • Fragmentation: Fragmentation is the breaking up of the body of a multicellular organism into two or more pieces. On maturing each piece grows to form a completely new organism.
     Example: Spirogyra.
     
     
   • Regeneration:
     • Regeneration is the ability of an organism to reproduce the lost parts of its body.
     • When some body part of an organism breaks suddenly, a new part similar to the lost (broken) part is created at the point of breaking after some time.
     • All broken parts thus develop into completely new organisms.
       
       
   • Budding:
     • A small part of the body of the parent organism grows out as a bud.
     • On maturing the bud gets detached from the parent and becomes a new organism.
       Example: Hydra, Yeast
       
       
   • Spore Formation:
     • Spores are microscopic reproductive units of plants.
     • Spores are covered by a protective coat.
     • When the spore coat bursts, the spores spread into air.
     • These air-borne spores germinate to produce new plants under favourable conditions if they settle on food.
       Example: Rhizopus, Mucor
       
       
6. Write a brief note on Vegetative propagation.
   ANS
   
   • Vegetative propagation is an asexual method of reproduction occurring only in plants.
   • New plants are obtained from old plants using their parts like roots, stem or leaves. Thus, reproductive organs are not involved in this method.
   • It involves development and growth of dormant buds present in the parts of old plants.
   • These dormant buds grow into a new plant under suitable conditions of temperature and moisture.
   • For example, buds present on bryophyllum leaves develop into a new plant.
   • There are several buds on a potato tuber. When these buds are planted in the ground, a new plant develops.
     
     
     
     
     
7. Describe various methods of Artificial Propagation.
   ANS
   
   • Artificial propagation involves development of a new plant from an old plant using artificial method.
   • The commonly used methods of artificial propagation are: (i) Cutting (ii) Layering (iii) Grafting.
   • CUTTING: A cutting of stem or shoot or leaf having buds on it is taken and its lower part is buried in the moist soil. After some days the cutting develops roots and grows into a similar plant. The advantage of this method is that many new plants can be grown from one plant in short time without seeds.
     Example: Rose, Bougainvillae.
     
     
   • Layering: In this method a part of stem is pulled towards the ground and covered by the soil. The covered part develops roots after some time and behaves as an independent plant. It is then separated from the parent plant and grows into a mature plant.
     Example: Lemon, Bougainvillae, Crysenthemum.
     
     
   • Grafting:
     • In this method two parts (stems) of different plants are joined together in such a way that they unite to grow as one plant.
     • The portion of the plant having roots is called 'stock'.
     • The portion of the plant without roots is called 'scion'.
     • By this method desirable characteristics of different plants can be combined.
     • This method is useful for plants whose seeds have long dormancy period and poor germination capacity.
     • Example: On the stock of lemon, a scion of lemon or orange can be grafted.
       
       
8. What is sexual reproduction? Describe its importance.
   ANS
   
   • Sexual reproduction is the process in which a male gamete and a female gamete unite to produce a zygote which develops into a new organism after some time.
   • IMPORTANCE:
     • Sexual reproduction introduces genetic variations which lead to a greater variety in offspring.
     • Genetic variations bring diversity of characters.
     • It gives different species of plants and animals to adapt to the changing environment. Organisms which adapt quickly to these changes survive and reproduce sexually.
     • Sexual reproduction plays an important role in the origin of new species through evolution.
9. Describe sexual reproduction in flowering plants.
   ANS
   
   • Flower is the reproductive part in higher plants.
   • The reproductive organs are located within the flower.
   • If the same flower contains both the male and female reproductive organs, the plant is known as bisexual.
   • The function of the flower is to produce male and female gametes and to ensure fertilization.
   • The male organ is called stamen and it produces male gametes.
   • The female organ is called carpel and it produces female gametes.
   • Female gametes are called ova or egg cells and they are present in ovules.
   • Male gametes are present in pollen grains and they fertilize the egg cells in ovules.
   • The fertilized egg cell develops within ovule which produces embryo and then entire ovule is converted into a seed.
   • Seeds germinate to produce new plants under favourable conditions.
     
     
10. Write a brief note on puberty.
    ANS
    
    • Puberty is the stage in the life of a human being when the reproductive organs show gradual changes in structure and they become functional.
    • A boy attains puberty at the age of 13-14 years whereas a girl attains puberty at the age of 12 years.
    • During puberty, testes in male start producing male gametes (sperms) and the sex hormone testosterone.
    • Similarly, ovaries in female start producing female gametes (ova) and sex hormones estrogen and progesterone.
    • During puberty hair grow in armpits and around genital organs between the thighs. This is common to both boys and girls.
    • In addition, in boys the body becomes more muscular, the voice deepens and shoulders and chest broaden. The penis grows and becomes capable to be erect.
    • In girls, the breasts show development and the reproductive system changes. These changes are necessary to accommodate developing child within mother's body and to breast-feed the child after birth.
    • This stage between childhood and adulthood is called 'adolescence'.
11. Describe reproductive system in human male with diagram.
    ANS
    
    • A pair of testes is the main reproductive organ in human male.
    • Testes produce male gametes,i.e., sperms and the male sex hormone testosterone.
    • Epididymis, vas deferens and penis are the accessory reproductive organs which facilitate the transfer of gametes to the site of fertilization.
    • Seminal vesicle and prostate gland are accessory reproductive glands.
    • The two oval shaped testes lie in a muscular sac called scrotum outside the abdominal cavity.
    • The temperature in the scrotum is 2 to 3° C lower than the body temperature. This temperature is suitable for the formation of sperms.
    • The sperms produced in testes are transported to penis through epididymis and vas deferens.
    • Vas deferens connects to the urinary duct coming from urinary bladder.
    • Seminal vesicle and prostate gland secrete fluids which mix with sperms and increase their mobility.
    • Urethra transfers sperms to penis and sperms pass into vagina through genital pore during mating.
      
      
12. Describe reproductive system in human female with diagram.
    ANS
    
    • Female reproductive system in humans is more complicated than that in male as fertilization and development of embryo takes place in it.
    • It consists of ovaries, oviduct, uterus and vagina.
    • Two ovaries are oval in shape and lie within the abdominal cavity.
    • Ovaries produce ova or eggs and secrete female sex hormones estrogen and progesterone.
    • There are two fallopian tubes (oviducts) which are funnel shaped and which receive the mature ova released by the ovary.
    • Oviducts carry the ova from ovary to the uterus, if it is fertilized by a sperm.
    • Uterus is a muscular bag where the fertilized egg further develops into embryo.
    • The lower tip of the uterus is called cervix.
    • The ovaries contain thousands of immature ovarian follicles which start maturing when a girl reaches puberty stage.
    • One of the ovaries produces one ovum every month which is carried to the fallopian tube.
    • During sexual intercourse, if the ovum is fertilized by a sperm, then the fertilized ovum gets implanted in the lining (wall) of the uterus and develops into a hollow ball of cells called embryo.
    • The embryo obtains nutrition from the mother's blood through a tissue called placenta.
    • The development of child within uterus takes about nine months before it is born.
      
      
13. Write an explanatory note on menstrual cycle (or menstruation) in human female.
    ANS
    
    • When a girl reaches puberty stage at the age of 10-12 years, the sex hormones cause ova to become mature.
    • Every 28 days one mature ovum is released by ovary into the oviduct.
    • The process of release of ovum is called ovulation.
    • Before ovulation, the inner wall of the uterus becomes thick and full of blood capillaries.
    • Thus, it becomes prepared to receive fertilized ovum.
    • If fertilization does not take place during certain time, the wall of the uterus disintegrates and blood vessels break.
    • The disintegrated tissue and the dead ovum come out of the vagina along with blood.
    • This is known as menstruation which lasts for 3 to 5 days.
    • When menstruation is over, the inner wall of the uterus starts becoming thick again so that it may receive the next fertilized ovum.
    • If the ovum is not fertilized, the menstruation takes place again.
    • This menstruation cycle is repeated every 28 days.
    • If fertilization occurs and the woman becomes pregnant, then menstruation stops temporarily.
    • At the age of about 50 years, menstruation stops permanently.
    • This is called menopause and the woman loses the capability to reproduce.
      
      
14. Write a note on Reproductive Health.
    ANS
    
    • The diseases which are transmitted by sexual contact with an infected person are called Sexually Transmitted Diseases (STD).
    • Syphilis is caused by bacterial infection by bacteria Treponema palidium.
    • Lesions in mucus membrane of urinogenital tract and ulcers are symptoms of syphilis.
    • Gonorrhoea is caused by bacteria Neissena gonorrhoea. It results in inflammation of urinogenital tract.
    • Both syphilis and gonorrhoea are curable diseases.
    • AIDS (Acquired Immuno Deficiency Syndrome) is caused by HIV (Human Immuno-deficiency Virus).
    • AIDS damages the immune system of the body and weakens body's protection against infections.
    • AIDS is a fatal disease.
    • Research work is in progress to find out medicines to cure AIDS.
    • In India, NACO (National AIDS Control Organization) creates awareness regarding AIDS and provides information about reproductive health.
    • Multiple pregnancies adversely affect a woman's health.
    • Different methods have been devised to avoid unwanted pregnancy. These methods are called contraceptive methods.
15. Describe different methods of contraception (Birth control or Prevention of pregnancy)
    ANS
    
    • Contraceptive methods used for the birth control are of three types: (i) Mechanical method (ii) Chemical method (iii) Surgical method.
    • Mechanical method:
      In this method, the entry of sperms in the genital tract is prevented by creating a mechanical barrier. Due to this the fertilization of egg cannot occur. Condom worn on penis or diaphragm worn in vagina by female work as mechanical barriers. IUCDs (Intrauterine Contraceptive Devices) like copper-T placed in uterus prevent pregnancy.
      
      
    • Chemical method:
      Pills are used by female in this method. The oral pills contain hormones which stop the production of ova and prevent fertilization. Vaginal pills contain chemicals called spermicide which kill the sperms.
    • Surgical method:
      In male, a small portion of vas deferens is surgically removed and both the cut ends are tied properly. This prevents the entry of sperms to urethra. The process is called Vasectomy.
      In female, a small portion of oviduct is removed and tied up. This prevents ovum from entering the oviduct. The process is called Tubectomy.
      
      
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    ANS