HOW DO ORGANISMS REPRODUCE

Reproduction is a process by which all living organisms give rise to new organisms similar to themselves (parents).

It is essential for the survival of the species since all living organisms have a limited life span.

Since the genetic material from one generation is passed in to the next, it not only maintains the continuity of species but also the continuity of the parental generation.

It enables a species to increase the total number of individuals.

Types of reproduction:

There are two main forms of reproduction. These are:

1.     Asexual reproduction

2.     Sexual reproduction

Asexual reproduction means formation of organisms without the fusion of gametes. The important features of asexual reproduction are:

i.   It involves only a single organisms or parent.

ii.   It gives rise to two or more individuals of the same kind. The individuals formed ate genetically identical to the parent.

iii.   The cell divisions are mitotic in nature.

iv.   It is a most common mode of reproduction in unicellular organism, some plants and lower multlicellular organisms like sponges and hydra. It is absent in higher invertebrates and all vertebrates.

Types of Asexual reproduction:

i.           Fission (binary fission, multiple fission)        ii.  Budding

         iii.        Spore formation                            iv.  Regeneration

          v.     Vegetative propagation                  vi.  Tissue culture

1.  Fission :

Fission means splitting. It occurs in unicellular organisms. The parent organisms split into two or more equal parts. Each part then develops as a separate individual. Depending on the number of individuals formed after splitting of the parent organism, fission is or two types.

a)     Binary fission:  The terms binary fissions “splitting of a single cell into   two”.

·        In this method, first the nucleus elongates and divides into two.

·        Then a constriction appears in the cell membrane which deepens further, dividing cytoplasm into two parts.

·        This way the parent cell divides into two daughter cells.

·        Each part then grows into an adult organism, similar to the parent.

·        Paramecium also reproduces by binary fission in the same number as explained in Amoeba in transverse plane but Euglena and Leishmania (the protozoan causing Kalaazar) reproduce by binary fission in longitudinal plane.  

 

b)    Multiple fission: Multiple fission means division of the parent body into a number of daughter organisms.

·        In this the parent nucleus divides repeatedly.

·        The nuclei move towards the periphery and each one is surrounded by a small amount of cytoplasm and cell membranes.

·        Finally each one of these structure gives rise to a new individual. The multinucleate body gives give to as many number of daughter individuals as the number of nuclei formed.

·        It is a common mode of reproduction in malarial parasite (plasmodium), when it invades the RBC of man.

      

2.  Budding:

In budding the new individual arises as an outgrowth (bud) from the parent. In can be seen in lower organisms like hydra and yeast.

a)     Hydra: In multicellular organisms like hydra, a bulge like projection as a result of repeated mitotic division grows in the parent body.

·        This bulge is called the bud.

·        This bud grows and develops organs like mouth and tentacles around it.

·        It grows to a full size and develops into a new hydra attached to the parent body.

·        Finally a constriction at the base separates the new hydra from the parent body.

                        

b)    Yeast:  In unicellular organisms like yeast (a fungus) a bud starts as a small outgrowth from the surface of an adult cell.

As it enlarges the nucleus of the adult cell divides and then the bud gets pinched off but still remains attached to the parent cell.

This in turn produces another bud at its tip and the process continue 3-4 times resulting in a chain of yeast cells.

3.  Spore formation: It is the most common type of asexual reproduction in majority of fungi and bacteria. The spores develop in a structure called sporangium. Sporangium develops on slender, erect fungal nuclei. Each nucleus with a bit of cytoplasm develops into a spore. A spore is a small microscopic structure with a thick wall. 

·        The wall of sporangium breaks releasing the spores in the air.

·        Sooner or later under favorable conditions in ground or substratum, each spore germinated into a hypha and grows into new plants.

   E.g. Rhizopus, mucor, penicillium.

                    

4. Regeneration: The process of getting back a full organism from is body parts are called regeneration. The simple animals like Hydra and Planaria show regeneration. This means that in these organisms, whole new organisms can be reproduced from their cut body parts. In other words or Hydra or planaria somehow get cut into a number of pieces, then each body piece can grow into a complete organisms.

Planaria is a flatworm which is found in freshwater ponds and slow-moving streams. Planaria possesses great power of regeneration. If the body of planaria somehow gets cut into a number of pieces, then each body piece can regenerate into a complete Planaria   by growing all the missing parts.

    

The regeneration of organisms from its cut body parts occurs by the process of growth and development. This happens as follows: the cell of cut body part of the organisms divide rapidly to make a ‘ball of cell’. The cell present in the ‘ball of cell’ move to their proper places within the ball where they have to inform various organs and body parts of the organisms. The cells then change their shape (or become specialized) to form different types of tissues. These different tissues form various organs and body parts of the organism. In this way a complete organisms is regenerated.

The complex multicellular organisms (like mammals) cannot give rise to complete individuals from their cut body parts through the process of regeneration.

Regeneration can be used to reproduce only those organisms which have relatively simple body organization consisting of only a few specialized cells (or tissues). In complex multicellular organisms, specialized cells make up tissues; tissues make up organs; organs make up organ system; and finally organ systems make up organisms. Since complex multicellular organisms have a very high degree of organization in their body, they cannot be reproduced from their cut body parts by the process of regeneration.

 5. Fragmentation- 

The breaking up of the body of a simple multicellular into two or more pieces on maturing , each of which subsequently grows to form a complete organisms is called fragmentation.

The organisms likes spirogyra and sea anemone can reproduces by these methods.

The main difference between fission and fragmentation is that in fission , a unicellular organism break up to form two daughter organisms whereas in fragmentation ,  a multicellular organisms breaks up to form two daughter organisms.

           

6. Vegetative propagation:

I.   It is the simplest and a rapid way of producing new plants in number of higher plants.

II.   It is development of a new plant from a vegetative part of plant like stem, root or leaf.

III.   Plants produced are identical to the parent plant. Same variety of fruit or flower can be produced year after year.

    Vegetative propagation can be natural or artificial. A number of ornamental plants, orchids, plants of economical or medicinal value are grown by artificial vegetative propagation. A number of flowering plants show natural vegetative propagation. Some of the common ways the plants propagate naturally are by 1. Stem 2. Root 3. Leaves

           

1.  By stem: Underground stems of potato, onion, banana and garlic etc.

2.  By roots: Roots of certain plants like guava, carrot , sweet potato and 

Dahlias have adventitious buds (adventitious buds are buds                                                                                 which are present at points other than the shoot tip and axil of leaves) on the roots which give out shoots that develop into new plants.

3.  By leaves: In Bryophyllum, the adventitious buds ate present along the

Notches of the leaves. During favorable conditions young plantlets develop from these buds. These plantlets fall off; grow roots into the soil and from independent plants.

Artificial vegetative propagation:

             Artificial vegetative propagation is tried by gardeners and horticulturists for large scale commercial purposes. Some or the common modes used are:

1.     Cutting   2.Layering and 3. Grafting

1.  Cutting: Cutting are short pieces of the plant which could be a stem, root, leaf or a bulb scale. When these are placed in moist soil with suitable conditions, they develop roots and shoot and grow into a new plant. Generally the cutting selected has some buds on them. At times stem cuttings are dipped into a hormone rooting powder to stimulate rooting.

                          

2.  Layering: In this method leaves from one of the branches are removed from a small portion. This small portion of the branch without leaves called layer is given a small cut and covered with soil. After two days the layer develops roots and it can be separated from the parent plant and planted separately.     

                  

3.  Grafting: Grafting is used to reproduce fruit tree and roses. In this method a twig (called the scion) is cut from the plant to be increased. It is then joined to the stem (called the stock) of a rooted plant. The cut surfaces are taped together. The graft heals on the rooted plant to give a new plant. Grafting is useful if plants are difficult to grow from seeds.

                       

Advantages of vegetative propagation:

1.     It is an easier, less expensive and rapid way of producing new plants under favorable conditions.

2.     The plants that cannot produce viable seeds such as banana, pineapple, orange, grape and produced by seeds.

3.     Plants produced by vegetative propagation bear flowers and fruits much earlier than those produced by seeds.

4.     Vegetative propagation takes much less time and so is highly suitable for plants that have small number of seeds, poor seed viability or ling periods of seed dormancy.

5.     Superior quality fruits or flowers can be produced by method of grafting.

6.     Since vegetative propagation gives rise to plants that are identical to plants, it can be used to preserve a stock of preserved varieties.

Sexual Reproduction in Flowering Plants:

The important features of sexual reproduction are:

1.     It involves two parents a different sex, like male and female.

2.     Each parent produces special sex cells called gametes. Male gamete is often referred as sperm and female gamete as ovum.

3.     The gametes are haploid and are produced as a result of meiotic division.

4.     The fusion of male and female gamete results in the formation of a single celled diploid zygote.

5.     The zygote undergoes repeated mitotic division and grows into an embryo that gives to multicellular organisms by cell differentiation.

6.     The organism formed is genetically different from both the parents and resembles both the parents in certain features only.

Some important terms:

Unisexual:  It refers to organisms being either male or female.

Bisexual or hermaphrodite: It refers to an individual that has both male and female sex organs.

Gonads: gonads are the reproductive or sex organs that produce gametes. 

Male gonad is called testis and produced sperms.

Female gonad is called ovary and it produced eggs or ova.

Gametes: These are specialized cells produced from gonads as a result of meiotic (reduction division) .These is of two types: sperms and ova

Fertilization: Fertilization can be defined as the fusion of a sperm and an egg to give rise to a fertilized egg or zygote.

Zygote: zygote is a singled celled structure formed by the fusion of a sperm with an egg ovum.

Types of fertilization:

I.   External fertilization: when the fertilization takes place outside the body of organism, it is called external fertilization.

In animals like fishes and frogs (amphibians), male and female come together and discharge their gametes in the surrounding water. The sperm fertilize the ova in water. This type of fertilization is called external fertilization.

II.   Internal fertilization: when fertilization takes place inside the body of female, it is called internal fertilization.

In animals like insects, reptile, birds and mammals including human beings, the made discharges the sperms inside the body of female during mating or copulation. The sperm fertilizes the ovum in the oviduct of female. This type of fertilization is called internal fertilization.

The structure associated with mating is called accessory sex organs.

Significance of sexual reproduction:

1.     It promotes diversity of characters in the offspring since offspring have the genetic material of both the parents.

2.     There is increased opportunity for new combination of character to appear in the offspring. It plays a vital role in the origin of species. At times characters hidden in the parents get expressed in the offspring.

3.     It results in variations. The individuals formed are genetically different from both the parents. Variation is necessary for evolution.

Sexual reproduction in plants:

Flowers are the reproductive organs in flowering plants.

Structure of a flower

A flower is a reproductive part of a plant. Though flowers differ in color, size and arrangement, their basic plan remains the same.

Part of a typical flower:

A typical flower has four whorls arranged around the receptacle or thalamus – the expanded portion of the stalk.

          Whorls: Starting from outside, the whorl are arranged

Sepals: They are outermost whorl generally green and leaf like.

              They protect the flower bud before it opens.

Petals: They form the second whorl, inner to sepals.

 They are generally large, colored and showy.

 They help in pollination by attracting insects.

          Stamens: Stamens are the male reproductive parts. Each stamen has two           

                 Parts, filament and anther.

a)     Filaments are a long slender stalk.

b)    Anther is a bilobed flattened structure present at the tip of filament. Each anther has four pollen sacs which contain pollen grains.

Each pollen grain produces two male gametes.

      Carpel or pistil: They form the fourth and the inner most whorl containing                                                                                                                             

                        Female parts. Each carpel has three parts.

a)     Stigma: It is attached to the style and receives the pollen grains.

b)    Style: it forms the neck of carpel to which stigma is attached.

c)     Ovary: it is swollen basal part. It contains ovules. Each ovule contains an egg, the female gamete.

At maturity, the pollen grains develop into anthers and egg cell into the ovules.

Pollination:

Pollination is the transfer if pollen grains from an anther to the stigma. After the pollen grains are shed from the anthers, they can reach stigma of a flower by a number of means. The flowers could be self pollinated or cross pollinated.

Types of pollination

A.   Self pollination:

It refers to the transfer of the pollens forms the anther of a flower, to the stigma of the same flower or to the stigma of another flower of the same plants.

e.g- china rose, maize

B.   Cross pollination:

It refers to the transfer or the pollens from the anther of a flower to the stigma of another flower of a different plant of the same species.

It involves two separates plants and outside agencies like wind, water, air or insects.

e.g- papaya, mulberry 

        

Agencies of scientific terms cross pollination

Winds – Anemophily

Water – Hydrophily

Insects – Entomophily 

Birds   – Orinthiophily

Bats - Chiropterophily

Fertilization in plants

After pollination, occurs fertilization in plant. The main events that lead t fertilization are as given below:

1.     Immediately after pollination, as pollen grains land in stigma, they give rise to pollen tubes.

2.     One pollen tube grows through the style and reaches the ovary where ovules are located.

3.     Each pollen tube has two male gametes.

4.     Pollen tube enters the ovule through a small opening called the micropyle.

On reaching the ovary, the pollen tube releases two male gametes into the embryo sac of ovule.

 

One male gamete fuses with                            other male gamete with the

the egg cell of the ovule.                                   two polar nuclei in the ovule      

          

It is known as fertilization or                              since it is fusion of 3 nuclei,

Syngamy and produces a                                     it is known as triple fusion.

fertilized egg or zygote.                                    (Triple fusion produces a                    (zygote is diploid in nature 2n).                           triploid nucleus and this 3n in nature. 

                                                                           

	It is called double                  Fertilization

Double fertilization: Since the process of fertilization occurs twice in the embryo sac, it is called double fertilization. It is unique to flowering plants.

Double fertilization includes two fusions – syngamy and triple fusion

i)                                                Male gametes+ egg cell = Zygote ( syngamy)

ii)                                              Male gamete + 2 polar nuclei =Triploid nucleus ( triplet fusion) 

Double fertilization = Syngamy + Triple Fusion

Results of double fertilization are:

i.                                              Zygote (2n) divides mitotically and forms the embryo plant.

ii.         Triploid nucleus (3n) gives rise to a mass of tissues called endosperm of seed. It provides nourishment to the growing embryo at the time of seed germination.                           

                                                          

 Summary of changes after fertilization

1. The ovary develops into the fruit.

2.The ovules develop into seeds.The seed contain the embryo or the potential plant. During the formation of fruit, rest of the flower withers away.

Germination:

If a seed lands where conditions are appropriate, i.e. water, oxygen and warmth are available, it will start to grow. Germination is when the embryo begins to grow. The beginning of the growth of seed is called germination of seeds. Germination begins when the seed absorbs water, swells and burst through seed coat . The water helps the enzymes to function in the seed. The enzyme digest the stored food in cotyledons ad make it soluble. The soluble food makes the radical and plumule present in the seed to grow .

The embryo grows a new root or radical and new shoot or plumule. The radical and plumule need food for growth and they get this food from the food store in the cotyledons.

         

                     

SEXUAL REPRODUCTION IN ANIMALS

Sexual Reproduction is the fomation of the new individuals by a process which involves the fusion of male and female gametes.

Reproduction in human beings

An animal having male sex cells called sperms in its body is called male.

An animal having female sex cells called ova in its body is called female.

The cells involved in sexual reproduction are called gametes. The male gamete is called sperm and female gamete is called or ovum or egg.

Fusion of gametes gives rise to a single cell called zygote.

Fertilization-        

The fusion of a male gamete with a female gamete to form a zygote during the sexual reproduction is called fertilization.

Puberty:

The age which the sex hormones (or gametes) begin to be produces and the boy and girl become sexually mature (able to reproduce) is called puberty.

The testes produce the male sex hormone called testosterone, and the ovaries produce two female sex hormones, oestrogen and progesterone.

The various changes which occur in boys at puberty are:  

Hair grows under armpits and in pubic regions (genital area) between the thighs. Hair also grows on other parts of the body like chest and face (moustaches, beard, etc). Body becomes more muscular due to the development of muscles. The voice deepens (or cracks). Chest and shoulders broaden. The penis and testes become larger. The testes start to make sperm.

The various changes which occur in girls at puberty are:

Hair grows under armpits and in pubic regions (this change is the same as in boys). Mammary glands (or breasts) develop and enlarge. The hips broaden. Extra fat is deposited in various parts of the body like hips and thighs. Fallopian tubes, uterus and vagina enlarge. Ovaries start release eggs. Menstruation (monthly period) start. Feeling and sexual drives associated with adulthood begin to develop. All these changes in girls are brought about by the female sex hormones ‘oestrogen’ and ‘progesterone’ made in ovaries. Please note that the hormones ‘oestrogen’ is also written and spoken as ‘estrogen’.

Human reproductive system:

 The reproduction systems in human beings become functional (or start functioning) at a definite age called puberty.

The male reproductive system

The human male reproductive system consists of the following organs: testes, scrotum, epididymis, vas deferens (or sperm duct), seminal vesicles, prostrate gland and penis. Testes are the primary reproductive organs in man (or males). The function of testes is to make the male sex cells (or male gametes) called sperms and also to make the male sex hormone called testosterone. The secretion of seminal vesicles and prostrate gland provide nutrition to the sperms and also make their further transport easier.

                        

   

The female reproductive system

The human female reproductive system consists of the following organs: ovaries, oviducts (which are also called fallopian tubes, uterus and vagina. Ovaries are the oval shaped organs which are inside the abdominal cavity of a woman near the kidneys. A woman has two ovaries. Ovaries are the primary reproductive organs in a woman (or female). The function of ovaries is to make mature female sex cells ( or female gamates) called ‘ova’ or ‘ eggs’, and also to make the female sex hormones ( called oestrogen and progesterone).

  

                                

                  Menarche and Menopause

Menarche: The begininning or commencement of menstruation at puberty is termed as menarche. In other words, the first monthly period or menstruation is called the menarche. It marks the beginning of the reproductive life of a woman. Normally it occurs between  11-13 years.

Menopause: At about the age of 50-55, the ovulation stops and the menstrual cycle is permanently discontinues. The ovarian as well as uterine cycles stop. This is known as menopause.

Menopause is marked by the stoppage of menstrual flow and other cycle events related to it.

After menopause the female loses the ability to reproduce.

Menopause also brings about a hormonal imbalance in the body( decreased oestrogen level), and hence is accompanied by other changes like loss of bone matter, increased body weight etc.

Reproductive life: The period between menarche and menopause i.e. between 12-50 years is called the normal reproductive life of human female.

                      Fertilization

Fertilization involves the fusion of a sperm and an ovum and restores the diploid number of chromosomes. The fertilized ovum formed is called zygote.

In human beings, the fertilization is internal. During mating, millions of sperms. About 200,000,000 are deposited in the vagina but only one out of these fertilizes the ovum. The sperms are highly active and motile but remain fertile for only about 12-24 hours in the female reproductive tract.

The sperms released in vagina, move up the uterus and then the fallopian tubes. Only a very small number of sperms reach the fallopian tubes because the female reproductive tract is strongly acidic. Finally only one sperm fertilizes an ovum. Fertilization occurs high up in the fallopian tube. A sperms may fertilize an ovum if mating takes place during the ovulatory phase.

The union of a sperm and am ovum gives rise to a zygote.

Fertilization is marked by the absence of menstrual flow.

Development of zygote after fertilization

-Immediately after fertilization, the zygote begins with repeated mitotic division. Also it starts moving down slowly , along the fallopian tube towards the uterus. In about 4-5 days, as a result of repeated divisions, it becomes a multicellular structure called an embryo and reaches the uterus.

-At about the 7^th day after ovulation, the embryo gets attached ( embedded ) to the thickened inner wall of uterus . this is called implantation.

-After implantation, a special tissue develops between the embryo and the uterine wall. This tissue is called placenta.

             

Placenta: Placenta is a disc- shaped connection between the mother and the embryo (foetus). When the embryo takes the characteristic human form, it is termed as foetus till birth.

-It is through placenta that the foetus exchanges respiratory gases, nutrients and excretory wastes with the maternal blood. Placenta supplies the foetus everything it needs for development. ( in the placenta , blood of the mother and the foetus never mix since exchange always takes place through the membrane.  CO₂  and wastes move from the foetus to maternal blood, and O₂  and nutrients from the maternal to foetal blood by diffusion).

Umbilical cord: it is during the development of embryo, that along with placenta, develops another structure called umbilical cord. Umbilical cord is a long and thick cord that runs between the foetus and the placenta( placenta is attached to the uterus).

-Umbilical cord is attached to the belly of the foetus. It contains the blood vessels taking foetal blood to and from the placenta.

                                                  

     Gestation:

Pregnancy or gestation refers to the condition of carrying developing foetus inside the uterus till birth. It begins with conception i.e. the fertilization of the ovum by a sperm, and continues until the birth of the baby.

Duration of pregnancy :

in human beings, the average duration of pregnancy is about 280 days ( or 40 weeks) i.e. approximately nine months.

It is calculated from the 1^st day of the last menstrual cycle. The newborn baby after 40 weeks of gestation weighs about 3.5 kg.

Parturition:

On completion of pregnancy or gestation, the birth of the fully formed foetus is called parturition.

Population control:

Human population is increasing at an enormous rate. It is estimated to become double in next 30-35 years. The increase in human population is not only adding to the already exploding population but is also causing a number of socio-economic problems. Also the frequent pregnancies have an adverse effect on the health of a woman.

  Birth control or fertility regulation methods:

To control over- population, the best method is the birth control. For this a number of scientific techniques have been developed to prevent pregnancy. These methods of birth control can be broadly classified into the following three categories.

1.     Barrier methods

2.     Chemical methods

3.     Surgical methods

Some common birth- control or fertility regulation methods  

s.n	Birth control Methods	Working of the birth- control method	Examples
1.	Barrier methods	-They prevent the entry of sperm in the female genital tract. Hence fertilization cannot take place.    -They include physical devices   that act as barriers.	Condoms –used by male Diaphragm and cervical caps – used by females
2.	Chemical methods	-These are specific drugs used by females.    -They are in the form of oral pills and vaginal pills    -Oral pills also known as birth control pills or oral contraceptives (OCs) conatain a combination of hormones. They prevent the production of ova in ovaries by acting on hypothalamus, pituitary and ovaries. Since ovulation does not occur, pregnancy cannot take place.  -Vaginal pills are chemical spermicides i.e. kill a large number of sperms.  -Intrauterine contraceptive devices (IUCDs) like copper T. Copper T is a small plastic device shaped like a letter T, with a fine copperwire wrapped around it. It is placed inside the uterus by a qualified doctor. It prevents implantation of ovum in the lining of uterus. The copper of copper T is slowly and continuously released into the uterus. Because of the presence of copper t, copper T is considered to be a drug.	Oral pills also called as oral contraceptives (OCs) and vaginal pills. Intrauterine contraceptive devices (IUCD) like copper T
3.	Surgical methods	-Surgical methods involve birth control by sterilization.   -They can be performed on either males or females and are almost 100% effective and are irreversible.   -In males, sterilization involves vasectomy i.e the removal of a portion of vas deferens from each testis. It prevents sperms from entering the urethra.  - In females, it involves tubectomy i.e the removal or ligation (tying ) of a section of each fallopian tube. It prevents ova from reaching the uterus. Vasectomy and tubectomy , both prevent contraception permanently.	Vasectomy in males. Tubectomy in females.

Reproductive health and sexually transmitted diseases (STDs)

The term health includes the physical, mental and social well being of a person.

Reproductive health includes aspects that ensure a responsible, safe and satisfying reproductive life.

1.  Importance of studying reproductive health

i.   It aims at providing awareness regarding the fertility regulation methods to both males and females.

ii. It gives the right, the freedom and choice to control child birth.

iii.  It gives people the ability to prevent and control sexually transmitted diseases (STDs).

iv. It helps people to manage disorders related to reproductive system.

2. Sexually transmitted diseases (STDs)

 Sexually transmitted diseases (STDs) are highly infectious diseases that spread form an infected person to a healthy person by sexual contact.

These diseases are caused by micro-organisms like viruses, bacteria, protozoans or fungi that are passed from one human being to another by sexual contact. Most of these diseases are curable, though there is no definite cure for AIDS( a sexually transmitted disease) till now. In most cases the common symptoms are burning sensation at urination and discharge from urethra or genital tract.

            

          Some common sexually transmitted diseases (STDs)  

Name of sexually transmitted diseases	Causative organism (micro- organism)	Symptoms
Gonorrhea	Bacterial	-Infects mucous membranes of the urino genital tract.   -Genital discharge, painful urination.     -Children born to afflicted mothers often suffer eye infections.
Syphilis	Bacteria	-Causes sores and lesions in the genital tract     -Burning sensation at urination     -Later causes sores in mouth.     -Can be deadly if not treated.
Trichomoniasis	Protozoa trichomonas	Vaginal irritation, itchining and discharge
AIDS (Acquired Immuno Deficiency syndrome)	HIV (Virus) Human  Immuno deficiency virus	-Destroy the immune system of body.     -Persistent cough and fever   -Body attacked by other diseases like pneumonia, T.B. and certain cancers. AIDS is a life threating disease. At present there is no vaccine to prevent and there is no cure. However AIDS is preventable.