REPRODUCTION IN ORGANISMS - III : LONG ANSWERS

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1. Describe fission as a method of reproduction.
   
   ANS :Fission occurs in unicellular organisms. Binary fission and multiple fission are its two types.
   
   BINARY FISSION :
   
   
   
   • An organism produces two unicellular organisms identical to the parent cell through mitotic division.
   • Amoeba, paramoecium, etc. reproduce by binary fission.
     
   
   
   MULTIPLE FISSION :
   
   
   
   • Under certain circumstances, the nucleus of a cell divides several times within the cell forming many nuclei.
   • Each nucleus is then surrounded by cytoplasm to form a separate unit.
   • All these newly formed cells then come out of the mother cell(parent cell) by breaking the wall and behave as a new organism.
   • Plasmodium, amoeba, paramoecium, etc. exhibit such reproductive event.
     
   
   
   
   
   
   
   
2. Describe budding as a method of reproduction.
   
   ANS :
   
   
   
   • Budding is observed in both unicellular and multicellular organisms.
   • In unicellular organisms, some part of the body swells out at one point and developes into a 'bud' due to the formation of nucleus and cytoplasm within it. This bud then separates from the parent cell and behaves as an independent organism. Sometimes the buds form a chain before being separated. Example : yeast.
   • In multicellular organisms like hydra, a part of its cylindrical body swells and develops into a bud. This bud then grows and separates from the mother's body to develop as an independent daughter animal.
     
   
   
   
   
   
   
   
3. Describe spore formation as a method of reproduction.
   
   ANS :
   
   
   
   • Spore formation is the most common method of asexual reproduction in majority of bacteria and fungi.
   • During spore formation, a structure called sporangium develops from fungal hypha which is a filamentous structure.
   • The nucleus in sporangium divides several times and forms many nuclei.
   • Each nucleus gets surrounded by cytoplasm and forms small unicellular structure called spore.
   • When sporangium bursts, the spores spread into the surrounding environment and germinate into new hypha forming mycellium which behaves as new organism.
   • Mucor and Rhizopus reproduce by this method.
     
   
   
   
   
   
4. Describe regeneration as a method of reproduction.
   
   ANS :
   
   
   
   • 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 new organisms.
   • Hydra, planaria, sponge and starfish reproduce by regeneration.
   • Some filamentous algae increase their number by this method. Algae filaments break frequently and each broken piece develops into independent algae. This is called fragmentation.
     
   
   
   
   
   
5. Describe role of sex hormones in humans.
   
   ANS :
   
   
   
   • Once a male reaches puberty, testes start producing sex hormone testosterone. Similarly, in females, ovaries start producing sex hormones estrogen and progesterone.
   • These hormones play an important role in the regulation of the processes of spermatogenesis (in male) and oogenesis (in female).
   • Sex hormones are also responsible for the structural development, maintenance and functions of accessory sex organs.
   • They induce secondary sexual characters at proper age.
   • The secondary sexual characters in male include : growth of hair on face, chest and other body parts; change in voice, aggressive behaviour and mental agitation.
   • Those in female include : changes in face and body, development of mammary glands, change in the pitch of voice, vigilant behaviour and sentimental approach.
     
   
   
   
6. What is the difference between menstruation and menopause ?
   
   ANS :When a woman (girl) attains puberty, her reproductive system becomes functional. As a result the ovary starts releasing ovum and this phenomenon is repeated after a definite period as a cycle. When an ovum is released the uterine wall gets ready for the implantation of fertilised ovum (zygote). If the ovum is not fertilised within certain period, it gets destroyed and the uterine wall disintegrates resulting in the breaking of blood vessels. The disintegrated tissue along with blood flows out through vagina. This flow of blood continues for about 3-5 days and is called menstruation.
   
   Menstruation, as a part of sexual cycle, starts at the age of about 10-12 years and its commencement indicates that the reproductive system of the woman has become active. The reproductive system then remains active up to the age of about 45-50 years and then becomes non-functional. The sexual cycle stops and menstruation ceases. This is called menopause. Thus, menopause marks the end of reproductive period of a woman.
   
   
7. Describe vegetative propagation in detail.
   
   ANS :
   
   
   
   • Development of a new plant from root, stem or leaf is called vegetative propagation.
   • Some higher plants exhibit this method of reproduction.
   • Examples : (i)Development of buds from the root of sweet potato.(ii)Development of buds on potato tuber.(iii)Development of buds on the margin of bryophyllum leaf.
   • Besides natural method, artificial vegetative propagation is also used to increase production. Cutting, layering and grafting are commonly used methods of artificial vegetative propagation.
     
   
   
   
   
   
8. Describe various methods of artificial vegetative propagation.
   
   ANS :
   
   
   
   1. CUTTING :
      
      
      
      • In this method, a piece of root, stem, leaf or sometimes a bud is sown in soil which develops into a new plant.
      • The piece of the plant sown in the soil develops roots downwards in the soil and aerial organs in the external environment.
      • this method is useful for large scale production which is greatly economical and profitable.
      • Example : sugarcane, grapes, rose, phalsa.
        
      
      
      
      
   2. LAYERING :
      
      
      
      • In this method, a branch of stem of a plant is bent towards the soil in such a way that some part of the branch remains inside the soil and its tip remains outside.
      • The part covered by the soil develops roots.
      • When this part is detached from the parent plant, it grows independently into a new daughter plant.
      • Example : Lemon, guaua, hibiscus, jasmine and bougainvillaea.
      • In plants like strawberry and raspberry, sometimes a branch comes into contact of the soil naturally and develops as a daughter plant after producing roots.
        
      
      
      
      
   3. GRAFTING :
      
      
      
      • Grafting is a method in which two parts of different plants are joined together in such a way that they unite to grow as one plant.
      • A part of an adult (mature) plant is tied up with a unit of soft plant to get early flowering in the soft plant.
      • The portion of the plant having roots on which grafting is performed is called 'stock'.
      • The portion of the plant which is grafted on the other plant is called 'scion'.
      • By this method, desirable characteristics of different plants can be combined.
      • This method is very 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. This method is widely used to increase the production of mango.
        
      
      
      
      
   
   
   
9. Describe reproductive system in human male.
   
   ANS :
   
   
   
   • A pair of testes is the main reproductive organ in human male.
   • Vas deferens and penis are the accessory reproductive organs.
   • Seminal vesicle, prostate gland and bulbourethral gland are the accessory reproductive glands.
   • The two testes lie in a muscular sac called scrotum outside the abdominal cavity in the region between legs.
   • The temperature in the scrotum is 3°C lower than that of the body. This temperature is suitable for the process of spermatogenesis.
   • The sperms produced in the testes are transported through vas deferens to the penis.
   • Sperms mix with the semen which is formed by the secretions of reproductive glands.
   • Semen provides movement to sperms so that they can reach the egg cell(ovum).
   • In male, urine and sperms get released through the same path called urinogenital path.
     
   
   
   
   
   
10. Describe reproductive system in human female.
    
    ANS :
    
    
    
    • The main reproductive organ in human female is a pair of ovaries located in the abdominal cavity.
    • The reproductive system includes ovaries, fallopian tube (oviduct), uterus, cervix, vagina and vaginal opening.
    • Accessory reproductive organs include labia major, labia minor and clitoris.
    • Ovaries possess many ovarian follicles which become mature at puberty stage and form graffian follicle. Graffian follicle form the structure of ovum.
    • Generally, one ovarian follicle becomes active alternately and forms one ovum.
    • The free end of the oviduct towards ovary is fimbricated and funnel shaped. It is known as oviductal funnel.
    • The oviducts on both sides join in the middle to form inverted triangular shaped muscular sac called uterus. The mouth of uterus opens into vagina through narrow cervix.
    • Vagina opens outside the body through vaginal opening.
    • There is a separate urinary opening above the vaginal opening. Thus, in female, the urinary passage and genital passage are separate from each other.
      
    
    
    
    
    
11. Describe sexual cycle in human female.
    
    ANS :
    
    
    
    • The sexual cycle in female starts at puberty stage when the development of ovum starts in ovary from ovarian follicle.
    • When the ovum develops (matures) up to a definite stage it is released by rupturing of ovarian follicle. This is called ovulation.
    • During first 13 days of cycle, development of ovum occurs and ovulation takes place on the 14th day. After ovulation, the ovum enters oviduct through oviductal funnel.
    • Simultaneously, the walls of uterus get ready for the implantation of embryo.
    • If fertilisation occurs, the implantation of embryo on the walls of uterus takes place and the process of supply of nutrition to embryo starts.
    • If fertilisation does not occur, the walls of uterus that got prepared for implantation in the form of blood-filled tissues start disintegrating.
    • This results in the breakdown of blood vessels and the broken uterine wall tissues come out through vagina along with blood. This is known as Menstruation.
    • Menstruation may last for 3-5 days during which abdominal pain is experienced.
    • Then the cycle is repeated. Generally menstruation cycle is repeated every 28-32 days.
    • The secretion of sex hormones at puberty stage is responsible for the commencement of menstrual cycle. With this the female attains the ability of conception.
    • The sexual cycle generally remains functional up to the age of 45-50 years. Then gradually the sexual cycle stops due to hormonal changes and menopause starts indicating the loss of the ability of conception.
      
    
    
    
12. Describe fertilisation and embryo development in humans.
    
    ANS :
    
    
    
    • During the sexual cycle of a female ovulation occurs on the 14th day and the ovum enters the fallopian tube.
    • If copulation occurs during the period when the ovum is present in the oviduct, sperms released in semen try to reach the ovum with the help of the fluid substances present in semen.
    • If one of the sperms can reach the egg(ovum) in the oviduct, then fertilisation takes place.
    • If fertilisation occurs, then the walls of uterus start further developments.
    • The embryo(fertilised egg) reaches the walls of the uterus and gets implanted on the wall.
    • An umbilical cord develops from the embryo to the uterine wall and supplies nutrition to the embryo from mother's body.
    • For the protection of the developing embryo, a structure (amnion) filled with amniotic fluid develops.
    • The birth of the child takes place, usually, after 40 weeks or 280 days. (this is the time for the development of the embryo into a mature baby).
    • Duration from zygote formation till birth of the child is called embryo developing time.
    • When the development of the embryo is complete, a new born child comes out of the mother's body by breaking the amnion. This event is known as delivery.
    • The calculation of embryo development time starts from the first day of last menstrual cycle.
    • The normal weight of the foetus(at the time of birth) should be about 3-3.5 kg.
      
    
    
    
    
    
13. Write an explanatory note on population control.
    
    ANS :
    
    
    
    • Growth of population is one of the biggest problems in the world. The population of India has crossed 1 billion mark and it needs serious attention . Also, frequent delivery can be dangerous to both the mother and the child as it results in ill health and the birth of a weak baby.
    • Keeping the growth rate of population limited by using some scientific devices is called population control.
    • Types of such devices include : (i) Birth-control tools (ii) Chemical devices (iii) Surgical devices.
    • Birth-control tools :
      1. A condom used by males prevents the entry of semen into vagina during copulation.
      2. A copper-T or a loop used by a female prevents implantation in uterus.
         
    • Chemical devices include birth-control pills containing hormones which prevent implantation.
    • Surgical methods :
      1. In males, the vas deferens is cut and tied up to prevent the transport of sperms. The method is called Vasectomy.
      2. In females, the oviduct is cut and tied up to prevent the transport of ovum. The method is called Tubectomy.
         
    • A doctor must be consulted before following any method of population control to avoid side effects.
      
    
    
    
    
    
14. Write a note on sexually transmitted diseases (STDs).
    
    ANS :
    
    
    
    • Sexually transmitted diseases are infectious and some times they prove fatal.
    • The diseases occurring due to unsafe sexual intercourse are called Sexually Transmitted Diseases(STDs).
    • Such diseases are caused by virus, bacteria, fungi and protozoans.
    • Syphillis is caused by Treponema Palidium.
    • Gonorrhoea is caused by Neissena Gonorrhoea.
    • Symptoms of STDs :
      • Inflammation of the passage of urine.
      • Lesions on the skin of urinary tract and vagina.
      • Itching sensation in penis or vagina.
      • Lesions on genital passage.
    • STDs are curable by proper treatment, so a doctor must be consulted immediately without hesitation when any of the symptoms of STDs become visible.
    • AIDS can prove fatal. Research work is in progress to find out medicines to cure AIDS.
    • WHO has given several guidences to prevent the spread of STDs and to protect human race.
    • In India, NACO (National AIDS Control Organisation) and other NGOs (Non-Government Organisations) are functioning to create awareness about STDs.
    • Individual Care :
      
      
      • One should keep awareness about the cleanliness of the reproductive organs.
      • There must be limit in developing friendship with opposite sex.
      • Use of birth-control tools during intercourse can prevent such diseases.
      • The best one is to learn to keep control on sexual desires.
      • Morality must be imposed as religious practice.
      
      
    
    
    
15. 
    
    ANS :