How do Organisms Reproduce? Notes

Introduction

REPRODUCTION

It is defined as a biological process in which an organism give rise to young ones similar to itself. The offspring grow, mature and in turn produce new offspring. Thus there is a cycle of birth, growth and death . reproduction enables the continuity of the species, generation after generation.

Reproduction in asexual reproduction

In asexual reproduction, an organism can reproduce without the involvement of another organism. Asexual reproduction is not limit to single-celled organisms. The cloning of an organism is a form of asexual reproduction. By asexual reproduction, an organism creates a genetically similar or identical copy of itself. The evolution of sexual reproduction is a major puzzle for biologists. The two-fold cost of sexual reproduction is that only 50% of organisms reproduce and organisms only pass on 50% of their genes.

Reproduction in sexual reproduction

Sexual reproduction typically requires the sexual interaction of two specialized organisms, called gametes, which contain half the number of chromosomes of normal cells and are created by meiosis, with typically a male fertilizing a female of the same species to create a fertilized zygote. This produces offspring organisms whose genetic characteristics are derived from those of the two parental organisms.

DNA Copying

DNA is the genetic material that defines every cell. Before a cell duplicates and is divided into new daughter cells through either mitosis or meiosis, biomolecules and organelles must be copied to be distributed among the cells. DNA, found within the nucleus, must be replicated in order to ensure that each new cell receives the correct number of chromosomes. The process of DNA duplication is called DNA replication. Replication follows several steps that involve multiple proteins called replication enzymes and RNA. In eukaryotic cells, such as animal cells and plant cells, DNA replication occurs in the S phase of interphase during the cell cycle. The process of DNA replication is vital for cell growth, repair, and reproduction in organisms. DNA copying is accompanied by the creation of an additional cellular apparatus, and then the DNA copies separate, each with its own cellular apparatus. Effectively, a cell divides to give rise to two cells.

Importance of DNA copying in reproduction

   The chromosomes in the nucleus of a cell contain information for inheritance of features from parents to next generation in the form of DNA (Deoxyribo Nucleic Acid) molecules. The DNA in the cell nucleus is the information source for making proteins. If the information is changed, different proteins will be made. Different proteins will eventually lead to altered body designs.

       Therefore, a basic event in reproduction is the creation of a DNA copy. Cells use chemical reactions to build copies of their DNA. This creates two copies of the DNA in a reproducing cell, and they will need to be separated from each other. However, keeping one copy of DNA in the original cell and simply pushing the other one out would not work, because the copy pushed out would not have any organised cellular structure for maintaining life processes.

• DNA copying helps in the transmission of information from parents to the offspring.
• And helps in the maintenance of chromosome number in the new cells.

Importance of variation

Variation of species over time is useful for the survival. Variation appear during reproduction whether organisms are multiplying asexually or sexually. The variations accumulate and pass on to more and more individuals with each generation. The diversity is small in case of asexually reproducing organism as it is caused by only errors of DNA copying mechanism.

 Significance of variation:

• Preadaptions Variations helps the organisms to tolerate drastic conditions by the process called preadaption.
• Evolution Evolutionary process progresses by the help of variations.
• Natural selectionUseful variations provide advantage to the individuals in the survival in nature.
• Artificial selectionBreeders select the right breeds based on the type of superior ones which is also due to these variations.
• Heredity Heredity is the transmission of genetic characters from parents to offsprings.
• Inherited traits These traits are controlled by genetic material of the individuals and are obtained from parents in inheritance.

Modes of reproduction

Single celled organisms

A single individual (parent) is capable of producing offspring. As a result, the offspring that are produced are not only identical to one another but are also exact copies of their parent.The term clone is used to describe such morphologically and genetically similar individuals. Many single-celled organisms reproduce by:

Binary fission

• Binary fission, where a cell divides into two halves and each rapidly grows into an adult (e.g., Amoeba, Paramecium). Many bacteria and protozoa simply split into two equal halves during cell division. In organisms such as Amoeba, the splitting of the two cells during division can take place in any plane.

YEAST

• In yeast, the division is unequal and small buds are produced that remain attached initially to the parent cell which, eventually gets separated and mature into new yeast organisms (cells).
• Many bacteria and protozoa simply split into two equal halves during cell division.

AMOEBA

• In organisms such as Amoeba, the splitting of the two cells during division can take place in any plane.

• Under unfavourable condition the Amoeba withdraws its pseudopodia and secretes a three-layered hard covering or cyst around itself. This phenomenon is termed as encystation.
• When favourable conditions return, the encysted Amoeba divides by multiple fission and produces many minute amoeba or pseudopodiospores; the cyst wall bursts out, and the spores are liberated in the surrounding medium to grow up into many amoebae. This phenomenon is known as sporulation.

LEISHMANIA

• Some unicellular organisms show somewhat more organisation of their bodies, such as is seen in Leishmania (which cause kala-azar), which have a whip-like structure at one end of the cell. In such organisms, longitudinal binary fission occurs in a definite orientation in relation to these structures.

PLASMODIUM

• The malarial parasite, Plasmodium, divide into many daughter cells simultaneously by multiple fission.

Fragmentation

Fragmentation, also known as splitting, is a form of asexual reproduction in which an organism splits into fragments. Each fragment develops into a mature clone genetically and morphologically identical to its parent. It is a type of asexual reproduction or vegetative propagation. Examples: Hydra, Spirogyra, etc.

 Hydra can reproduce asexually by budding and fragmentation. During fragmentation, the body divides into two parts with subsequent regeneration. If the animal is capable of fragmentation, and the part is big enough, a separate individual will regrow. Each of these fragments contains a protoplasm, so they grow into a new filament of the algae by cell division.

 Fragmentation occurs when the parent is matured and broken into pieces. It is seen in Spirogyra. A single cell type in the organism that is capable of growing, proliferating and making other cell types under the right circumstances.

Regeneration

Regeneration is one of the processes in which if an organism is cut into several pieces, each of its parts regrows to the original state. This process is carried out by specialized cells called stem cells. It takes place in organisms that have a very simple structure with very few specialized cells. For example, simple animals like Hydra and Planaria can be cut into any number of pieces and each piece grows into a complete organism. This is known as regeneration.

                     

 

The cells divide quickly into a large number of cells. Each cell undergoes changes to form various cell types and tissues. This sequential process of changes is known as development. The tissues form various body parts and organs.

However, regeneration is not the same as reproduction, since most organisms would not normally depend on being cut up to be able to reproduce.

   

Budding

In budding, a bud develops as an outgrowth due to repeated cell division at one specific site. These buds develop into tiny individuals and when fully mature, detach from the parent body and become new independent individuals.

Ex ; hydra and yeast.

 

Budding in Hydra	Budding in  Yeast
Hydra is a multicellular organism. Budding starts on the parent organism and then offspring gets detached from the parent surviving as an independent organisms.	Yeast is unicellular and it iteself is divided into one larger mother cell  and smaller daughter cell.
Multiple mitotic divisions are required for the formation of bud.	Budding here is similar to mitosis except that cytokinesis is unequal resulting in a unicellular bud.
Uses regenerative cells for reproduction.	When a yeast cell becomes mature then only it divides to form the mother cell will spend the cell cycle.

Vegetative propagation

• Vegetative propagation is a process in which plants reproduce from stems, roots and leaves. It is a form of asexual reproduction seen in plants. In fact, horticulturists use propagation methods such as grafting and budding to improve the plants.
• Because new plants can grow from older plants using vegetative propagation methods such as grafting and budding.
• Vegetative propagation occurs through vegetative plant structures.
• In non-vascular plants, the vegetative reproductive structures are gemmae and spores whereas, in vascular plants, the roots, stems, leaves, and nodes are the vegetative propagation structures. Also, we have learned about the meristem tissue in plants. This tissue helps in the vegetative propagation.
• It has undifferentiated cells which divide. As a result, it paves the way for the growth of the plant. Also, from the meristems, specialized permanent tissues are formed.

Types of Vegetative Propagation

Vegetative Propagation by Roots

In this process, new plants grow out of the modified roots called tubers. In fact, in some plant species, roots develop adventitious buds.  These buds grow and form new plants/sprouts under the right conditions. For example, Sweet potato and Dahlia. These sprouts can be separated from the parent plant and when planted in other areas, new plants are formed.

Vegetative Propagation by Stems

Vegetative propagation occurs through stems when new plants arise from the nodes. This is where buds are formed, which grow into new plants. stems that grow horizontally on the ground are called runners. As these runners grow, buds form at the nodes, which later develop the roots and shoots, resulting in the formation of a new plant. Example – Cyanodon; Mint etc.

Vegetative Propagation by Leaf

Plants like Bryophyllum, Begonia etc., have adventitious buds coming out from the notches of the leaves. These buds develop into new plants.

Cutting

Cuttings are the most common method employed by gardeners to grow new plants. A portion of the stem is cut and planted in the soil, which develops roots and further grows into a new plant.

Grafting

In grafting, we use two closely related plants to produce a new plant that has the desired, combined traits of both the parent plants. One plant is the stock, of which we take the root system and the other is the Scion, of which we use the shoot system. In this method of artificial vegetative propagation, we attach the scion to the stock of the second plant. In general, we use grafting for a variety of plants such as roses, apples, avocado etc.

Budding

In this method, we take a bud with a small portion of the bark from the desired plant. Then we insert it into a small slit made in the bark of the other plant. Next, we tie both the plants together and do not allow the buds to dry.

Spore Formation

Spore formation are formed by fungi and are often contained in a structure known as sporangium which on disintegration, release spores into the environment. When a spore land , it will germinate into a new fungus .Even in many simple multi-cellular organisms, specific reproductive parts can be identified. The thread-like structures that developed on the bread are the hyphae of the bread mould (Rhizopus). They are not reproductive parts. On the other hand, the tiny blob-on-a-stick structures are involved in reproduction. The blobs are sporangia, which contain cells, or spores, that can eventually develop into new Rhizopus individuals. The spores are covered by thick walls that protect them until they come into contact with another moist surface and can begin to grow.

Tissue Culture

• Cells from the growing tip of a plant are separated and are grown on a nutrient medium containing all nutrients and hormones necessary for plant growth.
• These cells form a mass called callus.
• The callus develops plantlets.
• These plantlets are transferred to the soil and grow as new individuals

Sexual reproduction

• Sexual reproduction is the process in which new organisms are created, by combining the genetic information from two individuals of different sexes. The genetic information is carried on chromosomes within the nucleus of specialized sex cells called gametes. In males, these gametes are called sperm and in females the gametes are called eggs. During sexual reproduction the two gametes join together in a fusion process known as fertilization, to create a zygote, which is the precursor to an embryo offspring, taking half of its DNA from each of its parents.
• In sexual reproduction, two gametes or germ cells, i.e. the male gamete called sperm and the female gamete called ovum, are involved. Both the sperm and ovum fuse together to form a zygote which develops into a new individual.
• Sexual reproduction is the most common life cycle in multicellular eukaryotes, such as animals, fungi and plants.
• Sexual reproduction does not occur in prokaryotes (organisms without cell nuclei), but they have processes with similar effects such as bacterial conjugation, transformation and transduction, which may have been precursors to sexual reproduction in early eukaryotes.
• In the production of sex cells in eukaryotes, diploid mother cells divide to produce haploid cells known as gametes in a process called meiosis that involves genetic recombination.
• The homologous chromosomes pair up so that their DNA sequences are aligned with each other, and this is followed by exchange of genetic information between them. Two rounds of cell division then produce four haploid gametes, each with half the number of chromosomes from each parent cell, but with the genetic information in the parental chromosomes recombined.
• Two haploid gametes combine into one diploid cell known as a zygote in a process called fertilization. The zygote incorporates genetic material from both gametes. Multiple cell divisions, without change of the number of chromosomes, then form a multicellular diploid phase or generation.
• In human reproduction, each cell contains 46 chromosomes in 23 pairs. Meiosis in the parents’ gonads produces gametes that each contain only 23 chromosomes that are genetic recombinants of the DNA sequences contained in the parental chromosomes. When the nuclei of the gametes come together to form a fertilized egg or zygote, each cell of the resulting child will have 23 chromosomes from each parent, or 46 in total.

 

                                                                                                                           

 

 

Reproduction in flowering plants

• All flowering plants perform sexual reproduction. The reproductive parts of the angiosperms are located in the flower.
• Parts of flower are petals , sepals, stamen and pistil. Among these stamen and pistil are reproductive parts of a flower. Stamen is the male reproductive part and pistil is the female reproductive part. They contain germ cells.
• Male germ cell is microspore and female germ cell is megaspore.
• Pollen grain is formed by microsporogenesis and megaspore is formed by megasporogenesis.

Microsporogenesis

Microspore is formed in the microsporangium, this contains four germ layers . The epidermis, endothecium, middle layers, and the tapetum. The tapetum nourishes the developing pollen grains. It contains more than one nucleus, dense cytoplasm and sporogenous tissue.

As the anther develops , cells of sporogenous tissue undergoes meiotic divisions to form four microspore tetrads. Each microspore tetrads is a potential pollen grain.

The process of formation of microspores from a pollen mother cell through meiosis is called microsporogenesis.

Megasporogenesis

The pistil or gynoecium represents the female reproductive part of the flower. Each pistil has three parts , the stigma, style and ovary. The stigma serves as landing platform for the pollen grain. Style is the elongated slender part beneath the stigma. The basal bulged part of the pistil is the ovary. Ovarian cavity (locule) inside the ovary is there in which placenta is located. Megasporangia arises from the placenta commonly called ovules. The megaspore mother cell undergoes meiotic division resulting in the production of four megaspores.The process of formation of megaspores from the megaspore mother cell is called megasporogenesis.

• Embryo sac formation

The functional megaspore develops into female gametophyte (embryo sac). The nucleus of functional megaspore divides mitotically to form two nuclei which moves to the opposite poles, forming 2-nucleate embryo sac.

Two more sequential mitotic nuclear divisions result in the formation of the 4-nucleate and later the 8-nucleated stages of embryo sac. After the 8-nucleate stage, cell walls are laid down leading to the organization of the typical female gametophyte of embryo sac.

6 of the 8 nuclei are surrounded by cell walls and organized into cells; the remaining two nuclei, called polar nuclei are situated below the egg apparatus in the large central cell.

• Embryo sac

There is a characteristic distribution of the cells within the embryo sac. Three cells are grouped together at the micropylar end and constitute the egg apparatus. The egg apparatus , in turn consists of two synergids and one egg cell. The synergids have special cellular thickenings at the micropylar tip called filiform apparatus, which play an important role in guiding the pollen tubes into the synergids. Three cells are at the chalazal end ,are called the antipodals. The large central cell has two polar nuclei . The a typical embryo sac at maturity is 8-nucleated and 7-celled.

Pollination

Pollination is the mechanism of transfer of pollen grains from anther of male reproductive(stamen) part to stigma of the female reproductive part(pistil).

Types of pollination

There are three types of pollination depending upon the source of pollen :

1. Autogamy
2. Geitonogamy
3. Xenogamy

Autogamy

In this type ,pollination occurs within the same flower . two types of flowers are involved in this :

Chasmogamous Flower These flowers are similar flowers of other species with exposed anthers and stigma. Cross-pollination can occur in them.

Cleistogamous Flower These flowers do not open at all. The anthers and stigma lies close to each other. There is no chance of cross-pollination in them.

Autogamy requires synchrony in pollen release and stigma receptivity. Anther and stigma should lie close to each other so that self pollination can occur.

Geitonogamy

In this type, pollination occurs not within the same flower but within the same plant. Transfer of pollen grain of one flower to the stigma of another flower of the same plant.Functionally ,this type of pollination is cross-pollination but genetically it is autogamy since pollen grains come from the same plant.

Xenogamy

In this type, pollination occurs in different plant . Genetically it is cross pollination. Transfer of pollen grain of flower of one plant to the stigma of another flower of the different plant.

Compatible pollination

Fertilization is the fusion of male gamete to the female gamete, which occurs through right pollen-pistil interaction. Pollination does not guarantee the transfer of the right type of pollen. If the wrong pollen land on the stigma, pistil recognize it and rejects it because pistil has the ability to recognize the appropriate pollen. This is known as compatible pollination.

After the compatible pollination, the pollen grains germinates on the stigma to produce a pollen tube through one of the germ pore. Pollen tube grows through the tissues of the stigma and style and reaches the ovary .

Pollen-pistil interaction

Events starting from landing pollen grain to the stigma uptill fertilization are referred to as pollen-pistil interaction. These events are :

• In some plants, Pollen grain shed at 2-celled stage(a vegetative and a generative cell) and in some ,shed at 3-celled stage(a vegetative cell and two male gamete) in such plants pollen tube carry two male gamete from the beginning.
• The generative cell divides and forms the two male gamete during the growth of the pollen tube.
• Tube reaches the ovary after entering in one of the synergids through filiform apparatus of the micropylar part.
• Tube reaches the ovule and fertilization occurs.

Double fertilization

After entering one of the synergids, the pollen tube releases the two male gamete into the cytoplasm of the synergid.

• One of the male gamete moves towards the egg cell and fuses with its nucleus, this is known as syngamy. This results in the formation of zygote.
• The other male gamete moves towards the two polar nuclei located in the central cell and fuses with them to produce primary endosperm nucleus(PEN).
• This fusion of three haploid nucleus is termed as triple fusion.
• This two types of fusion, syngamy and triple fusion is known as double fertilization.
• The central cell after triple fusion becomes the primary endosperm cell(PEC) and develops into endosperm while the zygote develops into embryo.

Endosperm

Endosperm development precedes embryo development. Primary endosperm cell divides repeatedly and form a triploid endosperm tissue. The cells of this tissue are filled with reserve food material and are used for the nutrition of the developing embryo.

The coconut water is nothing but free-nuclear endosperm made up of thousands of nuclei and the surrounding white kernel is the cellular endosperm.

Embryo

Embryo develops at the micropylar end of the embryo sac where the zygote is situated. The zygote gives rise to the proembryo and then globular, heart-shaped and mature embryo.

Dicot Embryo	Monocot Embryo
A typical dicotyledonous embryo consists of an embryonal axis and two cotyledons above the embryonal axis epicotyl is present ,which terminates with the plumule or shoot tip and below the axis is the hypocotyl which terminates in the radicle or root tip. The root tip is covered with the root cap.	Embryos of monocotyledons have only one cotyledon. The cotyledon of monocot is called scutellum, present at the lateral side of the embryonal axis. At the lower end of the embryonal axis, radical and root cap enclosed in an undifferentiated sheath called coleorhiza is present. Epicotyl has a shoot apex and a few leaf primordial enclosed in a hollow foliar structure ,the coleoptile.

Fruit and Seed Formation

Seed is the fertilized ovule and fruit is the fertilized ovary. Seeds is formed inside fruits. A seed consists of seed coat, cotyledon, and an embryonal axis. The cotyledons of the embryo are simple structures generally thick and swollen due to storage of food reserves. Mature seeds may be non-albuminous or albuminous.

Albuminous Seeds	Non-Albuminous Seeds
They retain a part of endosperm as it is not completely used up during embryo development . For eg; wheat , castor, etc.	They have no residual endosperm as it is completely consumed during embryo development. For eg; pea, groundnut etc.

The transformation of ovules into seeds and ovary into fruit proceeds simultaneously. The wall of ovary develops into the fruit called pericarp. Fruits are of two types :

True Fruit	False Fruits
The fruits that develops only from the ovary are true fruits. All fruits other than false fruits comes under this category.	The fruits in which there is involvement of other floral parts also are false fruits. For eg; apple, strawberry, etc

Reproduction in human beings

Growth and Development in humans

Growth and development are gradual and irreversible processes. Size and complexity of the body increase gradually. Growth in humans is divided into the following stages:

Infancy

From 1 month to 1 year of age is considered to be infant

Children hood.

From 1 year to 4 year of age is considered is considered to be child . At this stage growth is fast.

Puberty

Puberty is the period during which the reproductive system matures in boys and girls. In girls, puberty begins at the age of 11 years. In boys, it begins at the age of 12–14 years. Puberty continues till the age of 18 years.

Changes occur during puberty:

Changes in girls	Changes in boys
Ovaries mature and start producing ovum Pelvic girdle becomes broad Hair growth in the pubic region and skin in the pubic region becomes darker Enlargement of breasts The voice becomes shrill	Testes mature and start producing sperms Pectoral girdle grows Hair growth in the pubic region and skin in the pubic region becomes darker Development of moustache and beard Development of a deep voice

Adolescence

• Children between the ages of 11 to 19 years.The period of transition from childhood to adulthood is called adolescence.
• Adolescence  is a period of physical, mental and emotional changes.
• The spurt of growth in certain body parts creates confusion in teenagers. They start worrying about it.They start feeling lonely and do not feel comfortable to share their problems with others.
• Teenagers become highly sensitive about someone’s opinion.
• They tend to become angry or upset very easily.
• They prefer the company of persons their age.
• Due to hormonal changes, they experience depression.
• They feel the urge to become independent but are unsure about themselves.
• They have many questions about sex.
• This makes it important to counsel them in the right manner

Adulthood

It is from the age of 18 years onwards. An individual attains full growth and emotional stability.

 Male reproductive system

The male reproductive system is mostly located outside of the body. These external organs include the penis, scrotum and testicles. Internal organs include the vas deferens, prostate and urethra. The male reproductive system is responsible for sexual function, as well as urination.

Penis

The penis is the male external genitalia . it helps in the transfer of the male contents to the vagina. The enlarged end of penis called the glans penis and covered by foreskin.

Scrotum

The scrotum is the pouch that is situated behind the penis. The scrotum helps in maintaining the low temperature of the testes necessary for spermatogenesis(process of formation of the sperms).

Testicles

Male reproductive organs have a pair of testis. The testes are situated outside the abdominal cavity within scrotum. Each testis has compartments called testicular lobules. Each lobule contains 1-3 coiled structure called seminiferous tubules in which sperms are produced. Each seminiferous tubule is lined on its inside by male germ cell and Sertoli cells.

Male germ cells undergo meiotic divisions that results into sperm formation while Sertoli cells provide nutrition to the germ cells.

The interstitial spaces outside seminiferous tubules contains the blood vessels and Leydig cells .

Leydig cells produce the testicular hormone , androgens.

Male accessory sex organs

1. Rete testis
2. Vasa efferentia
3. Epididymis
4. Vas deferens

The sperms transfers from these accessory organs sequentially

\( \displaystyle \mathbf{Seminiferous}\text{ }\mathbf{tubules}~~\to ~~\mathbf{rete}\text{ }\mathbf{testis}~\,\,\to ~~~\mathbf{vasa}\text{ }\mathbf{efferentia}~~\to ~~\mathbf{epididymis}~~\to ~~\mathbf{vas}\text{ }\mathbf{deference}\)

These ducts stores and transport sperms from testis to the outside through urethra.

Male accessory glands

1. paired seminal vesicles
2. paired bulbourethral gland
3. 1 prostrate gland

Sperms then travel more downwards from vas deference which receives a duct from the seminal vesicle and open into the urethra. Secretions from the bulbourethral and prostate gland adds to the sperm passage and provide some nutrition to the sperms like calcium, fructose, enzymes, they also helps in the lubrication of the penis.

 Sperms

 The sperms are tiny bodies that consist of mainly genetic material and a long tail that helps them to move towards the female germ-cell. It has 4 parts :

1. Head
2. Neck
3. Middle piece
4. Tail

Head : this part contains nucleus containing chromosomal material. Anterior portion of the head contains the cap-like structure called acrosome. The acrosome is filled with enzymes that helps in the fertilization of the ovum. The head is covered.

Middle piece : this part contains energy source for swimming of the sperms i.e; mitochondria.

Out of the total sperms of the ejaculation ,  60% sperms must have normal shape and size and 40% of them must show vigorous motility .

 Female Reproductive System

Female reproductive system consists of :

1. External genitalia
2. Primary sex organ : Paired ovaries
3. Female accessory ducts :
4. Paired oviduct
5. Uterus
6. Cervix
7. Vagina

External genitalia: it consists of mons pubis, labia majora, labia minora, hymen and clitoris.The homologous structure of the penis in female is the clitoris.

Ovaries: The female germ-cells or eggs are made in the ovaries. They are also responsible for the production of some hormones.

 When a girl is born, the ovaries already contain thousands of immature eggs known as oogonia. No more oogonia cells form after birth. These oogonia starts division and only enter into the initial phase of division process i.e; meiosis-1 as primary oocyte. On reaching puberty, some of these start maturing.

Oviduct: this is also known as fallopian tubes . it has 4 parts : isthmus, ampulla, infundibulum and fimbriae. Ampullary-isthmus junction is the region of fertilization . fimbriae helps in taking up the ovum during ovulation from the ovary.

Uterus: The two oviducts unite into an elastic bag-like structure known as the uterus One egg is produced every month by one of the ovaries. The egg is carried from the ovary to the womb through a thin oviduct or fallopian tube.

Cervix: The uterus opens into the vagina through   the cervix. Cavity of cervix is called as cervical canal.

Vagina: The vagina along with cervix forms the birth canal. This part also welcomes the male sperms. all the discharges of the female reproductive tract release through it.

Fertilization

• The sperms enter through the vaginal passage during sexual intercourse. They travel upwards and reach the oviduct where they may encounter the egg.
• The fusion of sperm and ovum result into formation of the zygote.
• The fertilized egg (zygote) starts dividing and form a ball of cells or embryo. The embryo is implanted in the lining of the uterus where they continue to grow and develop organs to become foetus.

Implantation

• As soon as the zygote is formed, it starts developing.
• By the time it reaches the uterus, it is a mass of cells known as an embryo.
• It remains attached to the wall of the uterus throughout its development.
• The period of development of the embryo inside the uterus is called the gestation period.
• In humans, the gestation period is of 9 months, i.e. about 280 days.
• The embryo after completing three months of development is called the foetus.

Placenta 

• The placenta is a special tissue which provides food and oxygen to the foetus through a connecting cord known as umbilical cord.
• This is a disc which is embedded in the uterine wall. It contains villi on the embryo’s side of the tissue.
• On the mother’s side are blood spaces, which surround the villi. This provides a large surface area for glucose and oxygen to pass from the mother to the embryo.
• The developing embryo will also generate waste substances which can be removed by transferring them into the mother’s blood through the placenta.
• The development of the child inside the mother’s body takes approximately nine months. The child is born as a result of rhythmic contractions of the muscles.

What happens when the Egg is not Fertilised?

If the egg is not fertilised, it lives for about one day. Since the ovary releases one egg every month, the uterus also prepares itself every month to receive a fertilised egg. Thus its lining becomes thick and spongy. This would be required for nourishing the embryo if fertilisation had taken place. Now, however, this lining is not needed any longer. So, the lining slowly breaks and comes out through the vagina as blood and mucous. This cycle takes place roughly every month and is known as menstruation. It usually lasts for about two to eight days.

Reproductive health

Reproductive health refers to a total well-being in all aspects of reproduction like physical, mental and social.

• India is the first nation in the world to initiate various action plans at national levels towards attaining a reproductively healthy society.

These are :

Counselling and creating awareness among people about :

1.     the reproductive organs

2.      adolescence and associated changes

3.     safe hygienic sexual practices

4.     sexually transmitted diseases

5.     various contraceptive methods to prevent pregnancy

Sexually Transmitted Diseases

 Gonorrhoea  and Syphilis

• Caused by bacteria.
• Bacteria spread through sexual contact.
• Burning sensation during urination.
• Urethral discharge containing pus.
• Sores in genitals.
• Both diseases are curable.

 AIDS (Acquired Immuno Deficiency Syndrome)

• AIDS is caused by the infection of HIV (Human Immunodeficiency Virus).
• This virus attacks the immune system itself.
• HIV penetrates the T-lymphocytes.
• Reduction in the number of T-cells reduces the immunity of a person.
• HIV is transmitted by

• • Sexual intercourse
  • Sharing contaminated needles
  • Blood transfusion of contaminated blood
  • From the infected mother to the unborn foetus
• The 1 st of December is World AIDS Day.

Method to prevent unwanted pregnancy:

Hormonal Method:

Various hormonal preparations come in the form of tablets or pills, commonly called contraceptive pills.

Barrier Methods:

Condoms, diaphragms and spermicidals are used. Condoms are used by males while diaphragms and spermicidals are used by females.

Intra-uterine Devices (IUDs):

IUDs such as Lippe’s loop and copper – T are fitted in the uterus. They prevent fertilisation.

Surgical Methods:

In females, the fallopian tubes are ligated. This is called tubectomy. In males, the vas deferentia are ligated. This is called vasectomy.

Induced Abortion:

It is also known as Medical Termination of Pregnancy (MTP). If a woman becomes pregnant and the couple is not willing to have a baby, then the option of induced abortion is chosen.