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REPRODUCTION AND ITS IMPORTANCE
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It is the process by which living organisms produce new
individuals similar to themselves.
Reproduction ensured continuity of life on earth.
It is a bridge to hereditary transmission.
It involves a continuation of characters from the parents to
daughter cells by copying of DNA (Deoxyribose Nucleic Acid)
molecules present in the chromosomes of the cell.
Copying of DNAs is also not a fool-proof exercise, even minute
changes bring about variation in the blue print of the offsprings.
The useful variations are retained while the harmful ones do not
go beyond.
Actually, variations help the species to withstand drastic
environmental changes, thus save the species from becoming
extinct and promotes its survival for a longer time.
This inbuilt tendency of variation is the “basis” for Evolution.
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ASEXUAL REPRODUCTION
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It involves only one parent.
There is no formation and fusion of gametes.
The young ones formed are almost identical to each other as well as to the parent cell.
Asexual reproduction generally occurs during favourable environmental conditions and when
there is an abundance of food.
It is a faster method of reproduction.
Different forms of Asexual Reproduction:
Fission: The parent cell divides/splits into two daughter cells —Binary fission and splits into
many cells —Multiple fission.
Budding: A new organism is produced as an outgrowth of the parent body part.
Spore Formation: Spores are small, the bulb-like structure which develops at the top of the
erect hyphae of the fungus-plant, when released into the air germinate, into new individuals
after landing into food or soil.
Fragmentation: It is the accidental process when the broken pieces of an organism
(fragments) grows into a complete organism. Example, fragmentation in Spirogyra.
Regeneration: When simple animals like a hydra, planaria develop a new individual from
their broken older part it is known as regeneration. It is carried out by specialised cells which
grow large numbers of cells.
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ASEXUAL REPRODUCTION
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BINARY FISSION
In unicellular organisms when cell becomes fully
mature, it splits into two or more parts. It is called
the fission.
In organisms such as Amoeba, splitting can take
place in any plane.
However, organisms like Leishmania (cause Kala-
azar), which have a whip like flagella at one end,
binary fission occurs in a definite orientation in
relation to the flagellum.
Seen in bacteria, protozoa like Amoeba,
Paramecium.
In these first pseudopodia withdrawn (karyokinesis)
the nucleus of the parent cell divides and then the
cytoplasm divides (cytokinesis) resulting in the
formation of two daughter cells.
It occurs during highly favourable conditions.
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ASEXUAL REPRODUCTION
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MULTIPLE FISSION
Seen in Plasmodium, (a malarial parasite).
In this during unfavourable conditions, the parent
cell develops a thick resistant wall around itself
forming a cyst.
Within the wall, the cytoplasm divides many times
to form many plasmodia.
When conditions become favourable, the cyst wall
breaks and the Plasmodium are released.
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ASEXUAL REPRODUCTION
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BUDDING
Seen in Yeast (a fungus).
The parent yeast cell develops a protrusion or an
outgrowth at its upper end.
The nucleus of the parent cell divides and one of
them moves into the outgrowth which grows bigger
and finally separates from the parent cell to lead an
independent existence.
Very often if the conditions are highly favourable, a
chain of buds is formed.
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ASEXUAL REPRODUCTION
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FRAGMENTATION
It can be seen in Spirogyra. During this process filament
of spirogyra simply breaks up into smaller pieces upon
maturation.
These pieces or fragments grow into new individuals.
This process occurs under favourable conditions of
moisture, temperature, light and nutrient availability.
Seen in multicellular organisms which have a relatively
simple body organisation like Spirogyra.
Spirogyra has a filamentous body.
However, all multicellular organisms cannot show cell-by-
cell division as cells from tissues which form organs.
These organs are placed at definite positions in the body.
Hence, they need to use more complex methods of
reproduction.
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ASEXUAL REPRODUCTION
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REGENERATION
It is the ability to give rise to new organism. When the individual is cut or broken up into many
pieces. It can be seen in Hydra and Planaria and is known as regeneration.
Regeneration is carried out by specialised cells which re-divide to form a mass of cells from which
different cells undergo changes to become different cell types and tissues.
From this mass of cells, different cells undergo changes to become various cell types and tissues.
These changes take place in an organised sequence referred to as ” development.
However, regeneration is not the same as reproduction, since most organisms would not normally
depend on being cut up to be able to reproduce.
It is the ability of organisms to develop their lost parts.
Some organisms show have high regenerative capacity.
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ASEXUAL REPRODUCTION
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SPORE FORMATION
Some bacteria and lower organisms make spores.
During spore formation, knob like structure called
sporangium develops from the fungal hypha.
Sporangia contain spores that eventually develop into new
individual.
The spores are covered by thick walls that protect them until
they come in contact with moist surface or substratum and
can begin to grow (seen in Rhizopus; a fungus).
Rhizopus body is made up of thread-like structures called
hyphae.
The erect hyphae bear sporangia inside which reproductive
structures called spores are formed.
Spores are asexually reproducing bodies having a thick
protective wall.
They are produced during unfavourable times and help to
tide over the unfavourable environmental conditions.
When the spores fall on a suitable medium, each one forms
a new individual.
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ASEXUAL REPRODUCTION
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VEGETATIVE PROPAGATION
Method by which plants reproduce by their
vegetative parts such as roots, stems, and leaves.
Types of Vegetative Propagation:
It is two types:
I. Natural vegetative propagation.
II. Artificial vegetative propagation (Tissue culture).
Mint reproduces naturally by roots.
Sugarcane, jasmine by stems and Bryophyllum by
leaves.
In bryophyllum buds are produced in the notches
along the leaf margins and when they fall on the
soil, they develop into new plants.
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ASEXUAL REPRODUCTION
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IMPORTANCE OF VEGETATIVE PROPAGATION
Plants can bear flowers and fruits earlier.
Plants which have lost the ability to produce viable seeds can also reproduce by vegetative
propagation.
All plants are genetically almost similar to the parent plant.
Seedless varieties can be obtained.
The property of vegetative propagation is used by horticulturists in developing methods like
layering, grafting to grow many plants like sugarcane, roses, or grapes.
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ASEXUAL REPRODUCTION
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TISSUE CULTURE
The technique of developing new plants from a cell or tissue in a nutrient medium
under aseptic conditions.
The cell or tissue is placed in a nutrient medium where it forms a mass of cells called
callus.
This callus is then transferred to another nutrient medium where it differentiates and
forms a new plant.
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SEXUAL REPRODUCTION
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Sexual reproduction in plants, Sexual reproduction
in human beings.
The mode of reproduction that takes place with the
involvement of two individuals of two different
sexes i.e. male and female.
During sexual reproduction, male organism having
male sex organs produces male gametes i.e.
sperms which are small and motile and the female
organism having female sex organs produces ova
which are generally large and store food.
Male and female gametes fuse to form a zygote
that grows into a new organism.
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SEXUAL REPRODUCTION
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SIGNIFICANCE OF SEXUAL REPRODUCTION
Sexual reproduction involves DNA as well as cellular apparatus of two different
organisms which promotes diversity of characters in the offspring.
Since gametes are derived from two different organisms, it results in a new
combination of genes which increases the chances of genetic variations.
Sexual reproduction results in the origin of. new species.
Sexual reproduction involves division in the sex organs that reduces the DNA matter
to half so that the zygote formed after fusion has the same amount of DNA as the
parents it maintains DNA in a species.
Limitation of Sexual Reproduction: Sexual reproduction involves the process of
combining DNA from two different organisms which may bring some undesirable
features also.
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SEXUAL REPRODUCTION
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SEXUAL REPRODUCTION IN PLANTS
It occurs mostly in flowering plants. In fact, flowers are the reproductive organ of
plants.
Pollen grains of a flower transfer to the stigma of the carpel of the same flower (Self-
Pollination) or to the carpel of another flower (Cross-Pollination).
This transfer of pollens is achieved by agents like wind, water or animals.
After pollination, the pollen grains reach the egg cell in the form of a pollen tube.
Fertilization- The fusion between the pollen grain and female egg cell. It occurs inside
the ovary. The zygote is produced in this process.
The zygote divides several times to form an embryo within the ovule. The ovule
develops a rough coat and is converted into a seed.
Ovary grows rapidly and ripens to form fruit, while the seed contains the future plant
or embryo which develops into a seedling under suitable conditions. This process is
known as Germination.
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SEXUAL REPRODUCTION
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SEXUAL REPRODUCTION IN PLANTS
Stamens are male reproductive parts and produce pollen grains that contain male
gametes. Each stamen has two parts—
Filament i.e. stalk and Anther i.e. swollen top part which has large number of pollen
grains.
The carpel is the female reproductive part and produces ovules that contain female
gametes. It has three parts—Stigma which is top sticky part and receives pollen grains
during pollination. Style which is the middle long part and ovary which is the swollen
part and contains ovules. Each ovule has an egg cell i.e. female gamete.
The flowers may be bisexual i.e. having both stamens and carpels for example;
Mustard China Rose (Hibiscus).
The flower may be unisexual i.e. paving either stamens or carpels for example;
Papaya, Watermelon.
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SEXUAL REPRODUCTION IN PLANTS
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POLLINATION
The process of transfer of pollen grains from
an anther to the stigma of the flower is
pollination. Two types of pollination are:
(i) Self-pollination: The transfer of pollen grains
from the anther to the stigma of the same flower
or another flower of the same plant.
(ii) Cross-pollination: The transfer of pollen
grains from the anther to the stigma of another
flower or another flower of a different plant of the
same species. It generally takes place with the
help of some agents like insects, birds, wind and
water.
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SEXUAL REPRODUCTION IN PLANTS
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FERTILIZATION
Fertilization is the process of fusion of male and female gamete to form a zygote during
sexual reproduction.
Pollination is followed by fertilisation in plants.
The events are:
Pollen grains land on the stigma of the ovary.
Pollen tubes grow out of the pollen grains, travel through the style and reach the ovary,
through micropyle.
Pollen tube has two male germ cells. Each ovule has two polar nuclei and a female
germ cell (egg).
Pollen tube releases two male germ cells inside the ovule, one of them fuses with
female germ cell and forms a zygote which grows into the baby plant i.e. embryo, the
fusion is known as syngamy.
The other male germ cell fuses with two polar nuclei, the process is known as triple
fusion. So in flowering plants two fusions take place during fertilisation. It is called
double fertilisation.
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SEXUAL REPRODUCTION IN PLANTS
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POST FERTILIZATION
Post-fertilisation changes: After fertilisation the following changes takes place in the
flower.
Zygote divides several times and forms an embryo inside the ovule.
The ovule develops a tough coat and changes into the seed.
The ovary grows rapidly and ripens to form a fruit.
Petals, sepals, stamens, style and stigma shrivel and fall off.
Seed and its parts: The advantage of seed is that it protects the future plant i.e.
embryo.
Seed has two parts: Cotyledons and Embryo Cotyledons store food for the future plant.
Embryo has two parts: plumule and radicle. Plumule develops into shoot and radicle
develops into root.
The process of development of a seedling from the embryo under appropriate
conditions is known as germination.
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SEXUAL REPRODUCTION
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REPRODUCTION IN HUMAN BEINGS
Human beings show sexual reproduction.
Male parent produces male gametes called
sperms.
Female parent produces female gametes called
ova.
Sperms have tail and are therefore, motile.
They are produced in large numbers in the testes.
Ovum is bigger, non-motile and only one ovary
produces one ovum in one month.
There is no food stored in the sperms whereas
ova contain stored food.
Both the gametes are microscopic unicellular and
have half the number of chromosomes as
compared to the body cells.
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SEXUAL REPRODUCTION
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Male Reproductive System:
Male reproductive system consists of the following
components:
1 pair of testes
A system of ducts
o Epididymis
o Vas deferens or the sperm duct
o Urethra
A system of glands
o Seminal vesicles
o Prostrate gland
o Cowper’s gland
A copulatory organ called a penis.
One pair of testes are present in a bag-like structure called
scrotum which lies outside the abdominal cavity, hence
they are extra abdominal in position. This is so because
the testes have to be maintained at 1-3 degree lesser
temperature than the body in order to produce functional
sperms.
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SEXUAL REPRODUCTION
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Female Reproductive System:
It consists of the following components:
1 pair of ovaries
1 pair of fallopian tubes or oviducts
A uterus/womb
A vagina/birth canal
Each ovary is almond shaped and present
inside the abdominal cavity.
At the time of birth each girl child already
contains thousands of immature ova.
These ova start maturing only from the time of
puberty. Only one ovum is produced by one
ovary in one month and each ovary releases an
ovum in alternate months.
The release of an ovum from the ovary into the
abdominal cavity is known as ovulation.
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SEXUAL REPRODUCTION
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FERTILIZATION AND DEVELOPMENT
The semen is discharged into the vaginal tract during copulation.
The sperms travel upwards and reach the fallopian tube where one sperm fuses with
the ovum to form the zygote.
The zygote divides and re-divides as it descends into the uterus and the embryo gets
implanted in the endometrium.
The endometrium thickens so as to receive the embryo.
The embryo gets nutrition from the mother’s blood with the help of a special tissue
called placenta, which is a disk-like structure embeded in the uterine wall.
It contains finger-like villi on the embryo side, while on the mother’s side blood spaces
surround the villi.
Villi provides a large surface area for glucose and oxygen to pass from the mother to
the developing embryo and the wastes to pass from the embryo to the mother through
the placenta.
When the embryo starts resembling a human is formed, it is termed as a foetus. The
foetus continues
to develop inside the uterus for almost nine months after which the baby is delivered
as a result of rhythmic contractions of the uterine muscles.
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SEXUAL REPRODUCTION
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SEXUAL CYCLE IN FEMALE: MENSTRUATION
After puberty, only one egg is produced alternately from one ovary after a period of 28
days.
Egg in fallopian tube encounter sperms which enter through the vaginal passage
during sexual intercourse.
This fertilized egg (zygote) gets implanted in the lining of uterus which later forms
embryo.
Embryo gets nutrition from the mother’s blood with the help of special tissue called
placenta.
If the egg is not fertilized, if lives for about one day since the ovary releases one egg
every month, the uterus prepares itself every month to receive the fertilized egg.
Thus, its lining becomes thick and spongy. If it does not get zygote, the developed
lining slowly breaks down and comes out through the vagina as blood and mucus.
This cycle takes place roughly every month and is known as menstruation.
It usually lasts for about 2-5 days.
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REPRODUCTIVE HEALTH
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A number of diseases occur as a result of sexual intercourse if one of the partners is
infected. These are known as sexually transmitted diseases (STD’s). They can be
caused by bacteria for example; syphilis, gonorrhoea; or caused by a virus for
example; HIV-AIDS, warts etc. The transmission of these diseases can be avoided by
using birth control measures such as wearing a condom during the sexual act.
Birth control measures: They can be mechanical, chemical and surgical.
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REPRODUCTIVE HEALTH
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Mechanical methods: These are used to prevent the passage of semen to the
follopian tube :
(i) Use of condoms: Condoms are thin rubber tubes worn over the penis before sexual
intercourse. The semen gets collected in this and is not discharged into the vagina.
(ii) Diaphragm: It is a thin rubber fixed over a flexible metal ring which is fitted over the
cervix in a woman’s body by a doctor.
(iii) Intra Uterine Contraceptive Device (IUCD) or loop: It is inserted in the uterus and
its insertion causes certain secretion which prevents the implantation of the embryo in the
uterine wall.
Chemical methods
i. Use of spermicides: These are strong sperm-killing chemicals available in the form
of creams, jellies etc. which are injected into the vagina just before copulation.
ii. Oral contraceptive pills: These are hormonal pills which prevent ovulation but do
not stop menstruation.
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REPRODUCTIVE HEALTH
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Surgical methods
Vasectomy: It involves cutting and ligating the vas deferens in males.
Tubectomy: It involves cutting and ligating Reproductive organs the fallopian tubes in
females.
Medical termination of pregnancy (MTP) or abortions is carried out to eliminate
the developing embryo. This practice can, however, be misused to carry out female
foeticide which involves the killing of the female foetus. It should be avoided at all cost
as it disturbs the male-female ratio in a population.
