How do Organisms Reproduce ?

In this Chapter...

The Fundamentals of Reproduction

Types of Reproduction

Human Reproductive System

Fertilisation and Post-fertilisation Changes

Menstruation

Reproductive Health

! Sexually Transmitted Diseases

The process by which living organisms produce its own kind

Types of Reproduction

of individuals to maintain the continuity of species is

called reproduction. Like other essential life processes,

Reproduction is mainly of two types, i.e. asexual reproduction

reproduction is not essential to maintain life of an individual.

and sexual reproduction.

But is a fundamental feature of all known life, each individual

^● Asexual Reproduction It is a rapid mode of multiplication

organism exists as the result of reproduction.

in which one parent (either male or female) is involved. The

new individuals produced are identical to their parents.

The Fundamentals of Reproduction

^● Sexual Reproduction In this process, the gametes from

The process of reproduction involves the formation of DNA

parents of opposite sex (male and female) fuse together to

copy and other cellular apparatus required by the cells of an

form a zygote. This zygote develops further and gives rise to

individual. DNA is the blueprint of all the basic design of

new offspring. The individual produced by this method

organisms. It is present in the nucleus of a cell as a condensed

exhibits variation.

structure called chromosome. It acts as the information source

and helps in making different proteins and cellular machinery

I. Modes of Asexual Reproduction

of cell, which makes up the different body designs.

Asexual reproduction occurs in unicellular organisms by

fission, budding, spore formation, fragmentation, regeneration

Variations

(in animals) and vegetative propagation (in plants). It occurs in

DNA copying during cell division always causes some or

multicellular organisms by budding and regeneration.

other type of variations in newly formed cell. This brings the

These are as follows

differences found in the morphological and physiological

(i) Fission The process where a unicellular organism splits

features of an organism.

itself into two or more daughter cells. It is of two types,

Since no biochemical reaction is absolutely reliable,

i.e.

DNA copies generated are similar, but not absolutely

(a) Binary Fission In this process, parent cell divides

identical. Variations lead to evolution by increasing the

into two identical daughter cells, e.g. Amoeba,

chances of survival of some individuals. Hence, important for

Leishmania.

the survival of species.

In this process, nuclear division is followed by

(iv)

Budding A daughter organism is formed from a small

cytoplasmic division.

projection known as bud. It develops as an outgrowth due

Pseudopodia

to repeated cell divisions of the parent body. When fully

Parent cell

grown, it detaches to grow into a new independent

individual, e.g. Hydra.

Nucleus

Tentacles

Pseudopodia

withdrawn

Parent

Hydra

Nuclear

Growing

division

bud

New Hydra

Budding in Hydra

Cytoplasmic

division

(v)

Vegetative Propagation The process of obtaining complete

plant from any vegetative part of plant is called vegetative

propagation. This is mainly of two types

Two daughter

cells formed

(a)

Natural Vegetative Propagation The vegetative

Binary fission in Amoeba

propagation that occurs automatically in plants is called

natural vegetative propagation. It can be achieved by

(b) Multiple Fission In this process, parent cell

root, stem, leaf, etc, e.g. Bryophyllum.

divides into many identical daughter organisms

Bud

simultaneously, e.g. Plasmodium.

Many daughter cells produced

Nucleus

by multiple fission

Daughter cells

Cytoplasm

released

Leaf of Bryophyllum with buds

(b)

Artificial Vegetative Propagation The artificially made

Protective wall

Cell

vegetative propagules in plants by humans, is called

artificial vegetative reproduction, e.g. cutting, layering,

Multiple fission in Plasmodium

grafting, etc.

(ii) Fragmentation The parent body on maturation breaks

^● Grafting A small part of stem from one plant without

up into two or more small fragments, which later grow

roots (scion) is attached to the part with root (stock) of

into a complete new organism, e.g. Spirogyra.

another plant.

(iii) Regeneration In this process, all fragments or parts

^● Layering The development of roots on a stem, while

that are separated from the body develop in new

the stem is still attached to the parent plant is called

animals, e.g. sponge, Planaria, Hydra, etc.

layering.

^● Tissue culture It is a technique used for growing new

plants using living tissues (like flower buds, stems,

growing tips, leaves, etc.) in vitro in an artificial culture

medium.

^● Using this technique, large number of plants can be

developed from a single parent.

(vi)

Spore Formation It is a type of asexual reproduction

where blob-like structures called sporangia are

involved. These cells or spores have the ability to

germinate under favourable conditions forming new

plants, e.g. Rhizopus.

Regeneration in Planaria

Spores

^● Ovary It is the swollen bottom part of carpel. It contains

ovules having an egg cell (female gamete).

Sporangium

Stigma

Anther

Sporangiophore

Style

Filament

Carpel

Petal

Hypha

Ovary

Sepal

(Singular-hypha, plural-hyphae)

Spore formation in Rhizopus

Longitudinal section of flower

Pollination

II. Modes of Sexual Reproduction

The transfer of pollen grains from the anther of the stamen to the

In this type of reproduction, both sexes, i.e. male and

stigma of a flower is termed as pollination. The pollen grains can

female are involved. Sex cell or gamete of one parent

be transferred by various agents like wind, water, insects and

(male) fuses with the sex cell or gamete of another

animals.

parent (female). This results in production of a new cell

Pollination usually occurs in two ways

called zygote.

(i) Self-pollination The pollen from the stamen of a flower is

Thus, the sexual mode of reproduction involves two

transferred to the stigma of the same flower or another flower

major processes

of same plant.

(i) Formation of gametes by meiosis

(ii) Fusion of gametes

(ii) Cross-pollination The pollen from the stamen of a flower is

transferred to the stigma of another flower of different plant

1. Sexual Reproduction in Flowering Plants

of the same species.

Angiosperms bear the reproductive parts within the

Fertilisation

flower and their seeds are enclosed in a fruit. Most plants

have both male and female reproductive

It is the process of fusion of male and female gametes. It gives rise

organs in the same flower and are known as bisexual

to a zygote. As soon as the pollen lands on suitable stigma, it

flowers. While others have either male or female

reaches the female germ cells in ovary. This occurs via pollen

reproductive parts in a flower known as unisexual flowers.

tube. The pollen tube grows out of the pollen grain, travels

through the style and finally reaches the ovary.

A flower comprises of four main parts, i.e. sepals, petals,

stamens and carpels. Stamens and carpels are the

After fertilisation, ovule develops a rough coat around itself and gets

reproductive parts of a flower.

converted to seeds and ovary ripens as fruit.

(i) Stamen It is the male reproductive part of the

The seed contains future embryo that grows under suitable

flower.

conditions (germination). The fertilisation in the flowering plant is

shown in the given figure.

(ii) Anther It is a bilobed structure containing two

pollen sacs present at tip of stamen. These produce

Pollen grain

pollen grains that are yellowish in colour.

Stigma

Male gamete (Male germ cell)

(iii) Carpel (Pistil) It is the female reproductive part,

which is present in the centre of the flower. It

Pollen tube

comprises of three parts

^● Stigma It is the terminal part of carpel which may

be sticky. It helps in receiving the pollen grains

Ovary

during pollination.

Female gamete

^● Style It is the middle elongated part of carpel. It

helps in the attachment of stigma to the ovary.

Germination of pollen grain on stigma

2. Sexual Reproduction in Human Beings

(ii) Female Reproductive System It includes internal and

external sex organs that function in reproduction of new

Human beings can reproduce sexually after attaining puberty. It

offspring. In human, female reproductive system is

represents period of adolescence when reproductive organs

immature at birth and develops to maturity at puberty

start developing and sexual maturity is attained. Some changes

to be able to produce gametes, and to carry a foetus.

during puberty are common in males and females such as hair

growth in armpits and genitals, oily skin, acne, etc.

Oviduct or

Fallopian tube

Specific changes in boys include facial hair growth, hoarse

Ovary

voice, etc. In girls, these changes are enlargement of breast size,

Uterus

begining of menstruation, etc.

Cervix

Human Reproductive System

The system of organs required by males and females for the

Vagina

process of sexual reproduction is called reproductive system.

(i) Male Reproductive System It includes parts which

Female reproductive system

produce the germ cells and those which deliver these cells

at the site of fertilisation.

Parts and Details of the Female Reproductive System

Seminal vesicle

Parts

Details

Ureter

Bladder

Ovaries

^● Paired, oval-shaped organs located in the

abdominal cavity near the kidney.

Prostate gland

^● Produce thousands of ova or egg cells.

Penis

^● Secrete female sex hormones like oestrogen

Urethra

and progesterone.

Vas deferens

Oviduct

^● It has a funnel-shaped opening near the

Scrotum

(Fallopian tube)

ovary.

^● Carries ova or egg from ovary to the uterus.

Testis

^● It is the site of fertilisation.

Male reproductive system

^● These open into the uterus from both

the sides.

Parts and Details of the Male Reproductive System

Uterus (womb)

^● Hollow, pear-shaped, bag-like structure.

Parts

Details

^● The growth and development of foetus takes

Testes

^● Paired, oval-shaped male sex organs.

place.

^● Consist of seminiferous tubules, where the sperms are

Cervix

^● It is the lower and the narrower portion of

produced.

uterus which opens into the vagina.

^● Produce a male sex hormone called testosterone, which

brings about changes in appearance of boys at puberty.

Vagina

^● Receives the sperms from the male partner.

^● Serves as a birth canal.

Scrotum

^● Small pouch that contains testis.

^● Present outside the abdominal cavity. As sperms are

formed here, this requires a lower temperature than the

Fertilisation and Post-Fertilisation

normal body temperature.

Changes

Vas

^● Tube-like structure which connects testis to the urethra

^● Fusion of sperm with ovum is called fertilisation. It

deferens

in order to allow the passage of semen.

results in the formation of diploid zygote. This process

Urethra

^● Common passage for both the sperms and urine. It

takes place in the oviduct or Fallopian tube. The

never carries both of them at the same time.

formation of embryo is the result of cleavage and growth

Prostate

^● Secretes seminal fluid and nutrients.

in zygote.

gland and

^● Fluid and nutrients combine with sperm to form semen.

^● The embryo sinks downward, reaches into the soft

seminal

Milky, viscous fluid contains fructose, proteins and other

uterine lining and gets embedded. This process is known

vesicles

chemicals for nourishing and stimulating sperms.

as implantation.

Penis

^● External male genital organ.

^● A disc-like structure called placenta grows between the

^● Transfers sperms into the vagina of the female during

uterine wall and embryo. It has finger-like projections

copulation.

called villi, which provide surface area for the exchange

Sperms

^● Tiny and motile bodies that use their long tail to move

of nutrients, oxygen and waste products between the

through the female reproductive tract.

embryo and the mother.

^● Childbirth (after a gestation period of approximately

Methods

Examples

Details

9 months) occurs by strong rhythmic contractions of

Diaphragm

^● Rubber cup that is placed in the vagina

uterine muscles.

over the cervix.

Intra-Uterine

^● Copper-T placed in uterus by doctor.

Menstruation

Contraceptive

^● Used to prevent pregnancy.

In the absence of fertilisation, the uterine lining which

Device (IUCD)

^● Can cause side effects due to the

becomes thick and spongy to receive a fertilised egg, is no

irritation of uterus.

longer required. It sheds out as blood and mucus which

Hormonal

Oral

^● Contain hormones, which prevent

lasts for about 2-8 days and occurs every month. This

contraceptive

release of ovum, so that fertilisation

phase is known as menstruation.

pills

cannot occur. These disturb the

hormonal balance (levels of FSH and

Reproductive Health

LH) of the body.

It can be defined as the state of physical, mental and

^● Can cause side effects also.

social fitness to lead a healthy reproductive life. Good

Chemical

Spermicide

^● Applied in vagina.

reproductive health provides both male and female with

Kills sperms.

●

^● the fertility control methods.

^● Can only be used with condoms or

^● awareness about how to limit their family size.

diaphragm.

^● protection from infection and sexually transmitted

diseases.

Surgical

Vasectomy

^● Small portion of the sperm duct is cut or

tied properly. Therefore, the sperm

Sex Ratio

transfer will be prevented.

^● Prevents sperms from coming out of

The ratio of the number of females to the number of

urethra.

males in a population is known as sex ratio. A balanced

^● An irreversible process.

female-male sex ratio is necessary for a healthy society.

Tubectomy

^● Small portion of oviduct is cut or

tied properly. The Fallopian tube in

Population Size

the female gets blocked. The egg

The rates of birth and death in a given population

will not be able to reach the uterus

determine its size. The population size increases if the

and thus,fertilisation will not take

birth rate is higher than the death rate and vice-versa.

place.

^● Prevents the egg from meeting the

Methods of Family Planning

sperms.

^● An irreversible process.

The sexual act always carries the risk of potential

pregnancy. In order to avoid unplanned pregnancies,

many ways have been devised, which are called

Female Foeticide

contraception or birth control methods.

The killing of unborn girl child is called female foeticide. It is

Methods of Family Planning

happening because of misuse of ultrasound technique by which

people get to know the sex of the child. If it is female, they get it

Methods Examples

Details

removed by surgery.

Barrier

Condom

^● Rubber sheath worn over the

penis to stop sperm from

Sexually Transmitted Diseases (STDs)

entering the vagina.

^● Prevents transmission of

Sexually Transmitted Diseases (STDs) are caused by different

Sexually Transmitted

pathogens transmitted by an intimate contact between healthy

Diseases (STDs) and has no

person and an infected person.

side effect.

Some Common STDs

Infections Examples Causative Organisms

Comments

Bacterial

Gonorrhoea Neisseria gonorrhoeae

^● Contracted on during unprotected sexual intercourse with an infected person.

infections

^● Also passed by an infected mother to the developing foetus.

^● Infects ureter in men and cervix in women.

^● Treatment with antibiotics is effective.

Symptoms of gonorrhoea

^● Discharge of pus from penis and vagina.

^● Burning sensation on urinating.

Syphilis

Treponema pallidum

^● Syphilis is transmitted from person to person by direct contact with syphilis sores

These occur mainly on the external genitals, vagina, anus or in the rectum, can also

occur on lips and mouth.

^● Syphilis can be transmitted during vaginal, anal or oral sexual contact.

^● Pregnant women with the disease can pass it to their unborn children.

^● Can be cured by antibiotics.

Symptoms of syphilis

^● Appearance of sores on body parts.

^● Fever, ulcers, bone pain, liver disease and anaemia. These symptoms slow up

during the tertiary stage of syphilis.

Viral

AIDS

HIV

Incurable and fatal as it suppresses the immune system of the body. It can be

infections

(Acquired

transferred in following ways,

(Human

Immuno

Immunodeficiency

^● during unprotected sexual intercourse with an infected person.

Deficiency

Virus)

^● sharing needles and transfusion of HIV unscreened blood.

Syndrome)

^● from the mother to the child via placenta during pregnancy.

Genital

HPV (Human

^● Causes warts over external genitalia and perianal area.

warts

Papilloma Virus)

^● Podophyllum preparations are effective in treatment.