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10 –- Sci – Ch-8 – How do organisms Reproduce
Chapter-8
How do Organisms Reproduce
Introduction
Reproduction is one of the fundamental attributes of living organisms to create new individuals that
look similar to each other, i.e., it involves creation of a DNA copy. This process is essential for survival of
a species on earth thereby ensuring continuity of life. Various organisms use different modes of
reproduction depending on their body design. Reproduction in living organisms takes place by two
general methods: asexual method involving single organism and sexual method involving two different
organisms, male and female.
Asexual reproduction can occur by fission, budding, regeneration, spore formation and vegetative
propagation in plants and in some unicellular animals. Sexual reproduction in plants occurs by the
formation of flowers which may be unisexual or bisexual. In animals sexual reproduction takes place by
fusion of both male and female gametes resulting in the formation of zygote, which gives rise to
offspring.
The normal reproductive health must be maintained by providing all relevant information to create
awareness regarding family planning and sex related communicable diseases.
IMPORTANT TERMS AND CONCEPTS
Reproduction: It is the process of producing new individuals of the same species by existing organisms
of a species, i.e., parents.
Significance of Reproduction
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It allows perpetuation of species.
It increases the population of species.
It plays an important role in evolution by transmitting favorable variations from one generation
to another generation.
Body Design of Organisms: Organisms look similar because their body designs are similar;
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Reproduction at its most basic level involves making copies of the blueprints of body design.
DNA in the cell nucleus is the information source for making proteins and different proteins lead
to different designs.
A basic event in reproduction is the creation of a DNA copy.
DNA copying is accompanied by a cell division giving rise to two cells.
DNA copying always involves some variation; hence DNA copies generated are similar but not
identical.
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This tendency of variation during reproduction leads to evolution.
Importance of Variation in Organisms
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Organisms fill well-defined places or niches in the ecosystem with the help of reproduction.
Organisms having similar body designs use the same niche or place.
If a niche suitable for a population of organism is drastically changed, the population may be
wiped out completely.
But if some variations are there in few individuals of these populations, there could be chances
for survival.
For example, if there is a population of bacteria living in temperate water and if the water
temperature increases due to global warming, most of the bacteria will die. But, the variants
resistant to heat will survive and grow further.
Variation is thus important for survival of species.
Types of Reproduction: There are two main methods in which organisms give rise to new individuals –
Asexual reproduction and Sexual reproduction
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Asexual reproduction: It is the process of producing new organism from a single parent without
the involvement of sex cells or gametes.
Examples: Binary fission in Amoeba, Fragmentation in Spirogyra, Regeneration in Planaria,
Budding in Hydra, Vegetative Propagation in flowering plants like rose and Spore formation in
Rhizopus fungus.
Sexual reproduction: It is the process of producing new organism from two parents by making
use of their sex cells or gametes.
Examples: Human, fish, frogs, cats, dogs and most flowering plants.
Characteristics of Asexual Reproduction:
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Only one individual of an organism is involved, i.e., opposite sexes are not involved.
Cell divisions are either amitotic or mitotic.
The new individuals produced are genetically identical to their parents.
Asexual reproduction presents a rapid mode of multiplication.
Advantages and disadvantages of Asexual Reproduction:
Advantages
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Asexual reproduction is simple and fast.
Disadvantages
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Evolutionary change is not possible as no variation is produced. A species consequently cannot
adapt to changes in its environment.
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Asexual reproduction produces identical organisms’ generation after generation. In case of any
defect in the parent organism, the offspring also inherits it.
Modes of Reproduction used by single organisms: Asexual reproduction takes place as follows
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Fission
Fragmentation
Regeneration
Budding
Vegetative Propagation
Spore formation
These modes of reproduction depend on the body design of the organisms.
Fission: This is the simplest method of asexual reproduction n unicellular forms of life such as
Amoeba, Paramecium and other protozoa.
• Fission leads to the creation of new individuals.
• In the process of fission, the parent organism splits or divides to form two or more new
more organisms.
• Fission is of two types: binary fission and multiple fission
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Binary Fission: It is the division of one cell into two similar or identical cells.
In this method, the nucleus first divides amitotically into two, followed by the division of
cytoplasm.
The cell finally splits into two daughter cells.
In plants, binary fission can be seen in bacteria, yeast and Euglena.
Among animals, Amoeba and Paramecium reproduce through binary fission.
Binary fission in Amoeba
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Multiple fission in Paramecium
Multiple Fission: In multiple fission, many individuals are formed from a single
individual.
The nucleus of the cell divides repeatedly, producing many nuclei.
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Each nucleus is surrounded by a small amount of cytoplasm and many daughter cells are
produced within the cyst.
The cyst breaks up under favorable conditions and small off springs are liberated
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In plants, multiple fission is seen in many algae and in animals; a common example of
multiple fission is that of the malaria parasite (Plasmodium).
Fragmentation: Multicellular organisms with simple body organization such as filamentous
algae-Spirogyra break up into two or more small pieces or fragments upon maturation. These
fragments grow into new individuals. Among animals, flatworm show fragmentation of the body
which develops into new individuals.
Regeneration: It is the ability of a fully differentiated organism to give rise to new individual
organisms from its body parts.
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Small cut or broken parts of the organism’s body grow or regenerate into separate
individuals.
For example, simple organisms like Hydra and Planaria can be cut into any number of
pieces and each piece grows into a complete organism.
Regeneration is carried out by specialized cells which proliferate and make large number
of cells thus undergoing changes to become various cell types and tissues.
The changes taking place in an organized sequence is development.
Regeneration in Planaria
Budding: In budding a small part of the body of the parent grows out as a ‘bud’ which then
detaches and becomes a new organism.
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Hydra reproduces by budding using the regenerative cells.
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A bud develops as an outgrowth in hydra due to repeated cell division at one specified
site.
When fully mature, the bud detaches itself from the parent body and develops into new
independent individuals.
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Budding in Hydra
Vegetative propagation: In vegetative propagation, new plants are obtained from the parts of
old plants like stem, roots and leaves, without the help of any reproductive organ. There are two
ways of vegetative propagation:
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Natural vegetative propagation and
Artificial vegetative propagation.
Natural Vegetative Propagation: Various structures that take part in this type of
reproduction are roots, stem and leaves.
• Natural Vegetative Propagation by Roots: In some plants like Dahlia, sweet
potato, etc., the adventitious roots become thick, swollen and tuberous due to
storage of food.
• Natural Vegetative Propagation by Stems: Some plants reproduce by means of
stems. They may be aerial like runners, suckers or underground like ginger
(rhizome), potato (tuber), onion (bulb).
• Natural Vegetative Propagation by Leaves: The fleshy leaves of Bryophyllm
bear adventitious buds in the notches along the leaf margin.
• When the leaves fall on the soil, the buds develop into small plants under
favourable conditions.
• These plantlets on being detached develop into independent plant.
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Artificial Vegetative Propagations: Some plant growers have developed artificial
methods of vegetative propagation like cutting, layering and grafting which are used in
agriculture and horticulture.
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Cutting: In this type of propagation any part of the plant root, stem or leaf is cut
and buried partly in the moist soil.
Many plants like rose plant, Chrysanthemum, grapes are propagated by means
of cutting.
Layering: The adventitious roots are produced in the branch of the stem before
the plant is detached from the parent plant. The branch of stem is called a layer.
This process is utilized in the propagation of plant and the phenomenon is called
layering. Layering is used in the propagation of plants like Lemon, Guava,
Hibiscus, Bougainvillea, Jasmine, Raspberry, Strawberry and many ornamental
plants.
Grafting: In this method of reproduction, two plants of closely related varieties
are joined together so that they live as one plant.
The portion of a plant that is grafted on the other plant is called scion, and the
plant in which grafting is performed is called the stock.
This method is applied to improve variety of fruits like mango, apple, peas,
citrus and guava.
Advantages of Vegetative Propagation
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Vegetative propagation is a cheaper, easier and more rapid method of
propagation in plants than growing plants from their seeds.
The traits or characters of the parent plant are preserved by vegetative
propagation.
Better quality of the plants can be maintained by this method.
It results in propagation of those plants which do not produce viable seeds or
produce seeds with prolonged period of dormancy.
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The plants generated from vegetative means require less time to grow and have
the advantage of being more uniform and genetically similar to the parent
stock.
Disadvantages of Vegetative Propagation
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Vegetative propagation induces over-crowding.
There is no genetic variation, so there is less adaptability to the environment.
The disease of the parent plant gets transferred to the offspring.
The plants lose vigor.
New characters can neither be introduced nor undesirable characters be
eliminated.
Spore Formation: When a slice of bread is kept in moist dark place for a few days, spores of
Rhizopus present in air settle on the bread to form new fungus plants of Rhizopus.
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The Rhizopus consists of fine thread-like projections called hyphae. It has a knob like
structure which is involved in reproduction called sporangia, containing spores that
develop into new Rhizopus.
Tissue Culture: It is the production or propagation of new plants from isolated plant cells or small pieces
of plant tissue in a synthetic medium of culture solution. Tissue culture for producing new plants is done
as follows:
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Plants are grown by removing tissues or separating cells from the growing tip of the plant and
put in an artificial medium.
The plant tissue divided to form small group of cells or callus.
The callus is transferred to another medium containing hormones for growth and differentiation
that forms plantlets.
The plantlets produced are transplanted into pots and soil where they can grow to form mature
plants.
This technique is also known as micro-propagation in vitro because it takes place outside the
body of the parent plant in a test-tube using an artificial environment.
Micro-propagation technique is being used for the production of ornamental plants like Orchids,
Dahlia and Carnation.
Sexual Reproduction: It is a type of reproduction in which the two sexes, namely, male and female are
involved.
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The male sexual unit is known as male gamete or sperm while female sexual unit is termed as
female gamete or ova.
Thus, the two major processes, i.e., formation of gametes and fusion of gametes constitute
sexual reproduction.
Significance of Sexual Mode of Reproduction
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Sexual reproduction promotes diversity of characters in the off springs.
It results in new combinations of genes brought together in the gamete and this reshuffling
increases genetic variation.
It plays a prominent role in the origin of new species.
The sexual mode of reproduction incorporates process of combining DNA from two different
individuals during reproduction.
Flow chart showing Asexual and Sexual Reproduction
Asexual Reproduction
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Sexual Reproduction
Organisms
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B
Generation I Organism
Mate and Produce
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Produces
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Generation II Organism
Produces
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Generation III Organism
C
Mate and
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Produce
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Mate and
F
Produce
G
And so on.
And so on. (Hereditary characters remain the
same from one generation to the next.)
Hereditary characters vary from
one generation to the next.
Angiosperms: It is a phylum comprising of the flowering plants. The gametes are produced within the
flowers and the ovules are enclosed in a carpel.
Sexual Reproduction in Flowering Plants: The sexual reproduction in plants takes place in the following
steps:
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The reproductive parts of angiosperms are located in the flower.
Stamens and carpel are the reproductive parts of a flower which contain the germ cells.
The male organ of a flower called ‘stamen’ makes the male gametes, which are present in pollen
grains of the plant.
The female organ of a flower called ‘carpel’ ‘pistil’ makes the female gametes, which are present
in ovules of the plant.
The male gametes present in pollen grains fertilize the female gametes present in ovules.
The fertilized ovules grow and become seeds.
The seeds produce new plants.
Parts of a Flower: The flowers are usually bisexual, i.e., male and female reproductive parts are present
in the same plant.
The flower is attached to the plant by a stalk or pedicel.
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The main parts of a flower are – sepals, petals, stamens and carpels (pistil).
Sepals: are usually green, leaf-like parts in the outermost circle of a flower. The function of
sepals is to protect the flower in its initial stages when it is in the form of a bud.
Petals: are the colourful parts of a flower whose base lies inside the sepals. The function of
petals is to attract insects for pollination and to protect the reproductive organs, which are at
the centre of the flower.
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Longitudinal section of flower
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Stamen: and carpels constitute the reproductive parts of a flower.
Stamen: is the male reproductive organ of the plant. A flower usually has a number of stamens
in it.
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Germination of pollen on stigma
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Each stamen is made up of two parts a filament, the stalk of stamen and an anther, the swollen
top of stamen. Anther is the upper bilobed part and each lobe contains two pollen sacs within
which numerous pollen grains are produced that are yellowish in colour.
Carpel (Pistil) is present in the centre of a flower and is the female reproductive organ of the
plant. It is made up of three parts – stigma, style and ovary
Stigma is the terminal part of carpel, which may be sticky and helps in receiving the pollen
grains from the anther of stamen during pollination.
Style is the middle elongated part of the carpel which connects stigma to the ovary.
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Ovary is the swollen bottom part of a carpel, which contains ovules and each ovule has an egg
cell – the female gamete. Carpel in a flower is surrounded by a number of stamens.
Unisexual: It is the plant whose flowers contain either stamens or carpels but not both.
Example: Papaya, Watermelon.
Bisexual: It is the plant whose flowers contain both stamens and carpels. Example: Hibiscus,
Mustard.
Pollination: It is the transfer of pollen grains from the anther of a stamen to the stigma of a carpel. The
pollen grains are transferred by many agents, such as insects (bees and butterflies), birds, man, wind
and water.
Pollination is of two types – self pollination and cross pollination.
Self Pollination: It is the transfer of pollen grains from the anther of a flower to the stigma of the same
flower or another flower of the same plant. It is seen in pea and China rose plant.
Advantages:
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Self pollination in bisexual flowers ensures continuity of the race.
It helps to preserve the parental characters, as the gametes from the same flower are involved.
It is not necessary for flowers to produce nectar or scent or be colourful.
Disadvantages:
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New varieties cannot be obtained by self pollination.
The genetic defects of the breed cannot be removed.
Repeated self pollination leads to loss of vigour and vitality of the species.
Cross Pollination: It is the transfer of pollen grains from the anther of one flower to the stigma of
another flower of a different plant of the same species. It is common in majority of flowering plants.
Cross pollination occurs with the help of two main groups of agents – biotic such as insects, birds and
man; and abiotic such as wind and water.
Advantages:
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Cross pollination results in healthier offsprings.
Seeds produced by cross pollination have much better germinating capacity.
More abundant and viable seeds are produced.
Variations are introduced by cross pollination.
Disadvantages:
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Plants have to depend on external agencies for pollination.
The pollen grains have to be produced in large quantity to ensure pollination.
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Gametes: The cells involved in sexual reproduction are called gametes. The male gametes in animals are
called ‘sperm’ or ‘spermatozoan’ and the female gamete in animals are called ‘ovum’ or ‘eggs’.
Zygote: The cell which is formed by the fusion of a male gamete and a female gamete is called zygote,
i.e., it is a ‘fertilized ovum’ or ‘fertilized egg’.
Embryo: It is the stage of development between the zygote or fertilized egg and the newly formed
offspring.
Fertilization: It is defined as the fusion of a male gamete (sperm) with a female gamete (an ovum or egg)
to form a zygote during sexual reproduction.
Fertilization in Plants: Pollination is followed by fertilization in plants.
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After the pollen lands on a suitable stigma, it has to reach the female germ cells in the ovary.
The pollen tube grows out of the pollen grain through the style to reach the ovary.
After fertilization, the zygote divides several times to form an embryo within the ovule.
The ovule then develops a though coat and gets converted into a seed.
The seed contains the future embryo which develops into seedling.
The ovary develops and ripens to form a fruit.
The process of double fertilization occurs inside each embryo sac, in which two fusions, syngamy
and triple fusion take place.
When one male gamete fuses with the egg contained in the embryo sac of the ovule, this fusion
of male and female gametes is called syngamy and its product is the zygote.
The other male gamete fuses with the two polar nuclei and this process is called triple fusion,
where three nuclei are involved in the fusion process, one male gamete and two polar nuclei.
Germination
Germination: It is the initial stages in the growth of a seed to develop into a seedling under appropriate
conditions.
Reproduction in Human Beings:
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The reproductive organs of human beings, i.e., testis in male and ovary in female become
functional only after attaining sexual maturity.
In males, sexual maturity is attained at the age of 13-14 years, while in females at the age of 1012 years. This is known as the age of puberty.
The testes and ovary produce viable gametes and also secrete hormones like testosterone (male
hormone from testes) and estrogen and progesterone (female hormones from ovary).
Sexual Maturity in Human Beings: Various changes take place in human body at the time of sexual
maturity or puberty.
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Changes common to both Boys and Girls:
Thick hair growth in armpits and genital areas between the thighs.
Thinner hair on legs, arms and face.
Oily skin and appearance of pimples.
Changes different in Boys and Girls:
In Girls
Breast size begins to increase.
Darkening of nipple skin.
Start of menstruation.
In Boys
Thick facial hair growth.
Voice begins to crack.
Penis occasionally begins to become enlarged and erect.
Puberty: It is the age at which the sex hormones or gametes begin to be produced and the boy or girl
becomes sexually mature.
Male Reproductive System: It consists of portions that produce the germ-cells and other portions that
deliver the germ-cells to the site of fertilization. The human male reproductive system consists of the
following organs:
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Testes: (singular testis) are the oval-shaped primary reproductive organs in man. A pair of testis
lies in a small sac-like muscular structure outside the abdominal cavity called scrotum. The
function of testis is to produce sperm and male sex hormone called testosterone. The scrotum
provides the optimal temperature for formation of sperms.
Epididymis: is a coiled tube-like structure firmly attached to the testis and serves as the
storehouse of sperms. Inside the epididymis, sperms become mature and develop motility.
Vas Deferens: The sperms are carried by a long tube called vas deferens or sperm duct into
organs called seminal vesicles, where the sperms get nourished and stored.
Urethra: is a common duct for the passage of both urine and spermatic fluid. Urethra carries the
sperms to an organ called penis which opens to the outside through a male genital pore.
Penis: forms the external male genital organ. It is a copulatory organ with thick muscular walls.
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Accessory Glands: Seminal vesicles are a pair of thin-walled muscular elongated sac which
secretes fluid for nourishment of sperms.
Prostate glands: also produce fluid which is released in the urethra along with secretion of
seminal vesicle. The secretion of accessory glands together with sperms is called semen.
Sperms: are tiny bodies that consist of mainly genetic material and a long tail which help them
to move towards the female germ cell.
Human – male reproductive system
Female Reproductive System: The female germ-cells or eggs are made in the ovaries and are
responsible for the production of some hormones. The human female reproductive system consists of
the following organs.
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Ovaries: are pair of small and oval-shaped organs, located in the abdominal cavity near the
kidney. Ovaries are the female primary reproductive organs which perform dual functions of
production of female gamete or ovum and the secretion of female sex hormones, estrogen and
progesterone.
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Human female reproductive system
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Fallopian tube or Oviduct: are pair of long convoluted tubes that carry ova or eggs from the
ovary to the uterus. The fallopian tube has a funnel-shaped opening near the ovary. These tubes
from both the sides open into an elastic bag-like structure, the uterus.
Uterus: or womb is hallow, pear-shaped organ within which the embryo develops. Its upper
portion is broader, while its lower portion is narrower, called cervix.
Vagina: The uterus opens into the vagina through the cervix. Vagina is a tubular structure called
“birth canal”. It receives sperms from the male and also serves as the passage through which the
fully developed foetus is born.
Sexual Reproduction in Human Beings:
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The male gamete (sperm) is introduced inside the female genital tract (vagina) by the process of
copulation or mating. Fertilization occurs in the fallopian tube.
Sperms are highly active and mobile which move up through cervix into the uterus and then
pass into the fallopian tubes.
In the fallopian tube only one sperm fertilizes the ovum to form a zygote. This is called
fertilization.
Fertilization occurs only if copulation takes place during the ovulatory period.
The embryonic development of the zygote starts immediately in the fallopian tube and
pregnancy starts while menstruation stops.
The embryo moves down to reach the uterus. The embedding of embryo in the thick inner lining
of the uterus is called implantation.
Then, a special tissue develops between the uterine wall and the embryo (foetus) called
placenta, where the exchange of nutrients, oxygen and waste products takes place.
The time period from the development of foetus inside the uterus till birth is called gestation.
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The act of giving birth of the fully developed foetus at the end of gestation period is termed as
parturition.
The development of the child inside the mother’s body takes approximately nine months.
Menstruation:
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The breakdown and removal of the inner, thick and soft lining of the uterus along with its blood
vessels in the form of vaginal bleeding is called menstrual flow or menstruation.
The cycle of events taking place in the ovaries and uterus every twenty eight days or roughly one
month and marked by the menstrual flow is called menstrual cycle or sexual cycle in human
female. It lasts for about two to eight days.
Reproductive health is all those aspects of general health which help a person to lead a normal, safe
and satisfying reproductive life.
Sexually Transmitted Diseases: (STDs) are the diseases which are spread by sexual contact from an
infected person to a healthy person. They are caused by various micro-organisms that live in warm and
moist environments of the vagina, urethra, anus and mouth. Some of the common sexually transmitted
diseases are
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Gonorrhoea: It is caused by bacterium Neisseria gonorrhoea. It is characterized by inflammation
of urinogenital tract and the patient feels burning sensation during urination. This bacterium
infects the ureter in men and cervix in women.
Syphilis: It is caused by bacterium Treponema pallidium. It is characterized by lesions in the
mucous membrane of urinogenital tract and ulcers on genitalia.
Trichomoniasis: It is caused by protozoan Trichomonas vaginalis. It is characterized by some
vaginal discharge at the urinogential tract of the female.
AIDS (Acquired Immune Deficiency Syndrome): It is caused by a virus called HIV (Human
Immunodeficiency Virus) which suppresses the body’s immune mechanism and thereby making
it susceptible to any disease.
Mode of transmission of AIDS is as follows:
• By having sexual contact with an infected person.
• By the transfusion of blood from an infected person.
• Through infected needles used for injection.
• Through the placenta from the mother to child during pregnancy.
Methods to Avoid Pregnancy: A number of techniques have been developed to prevent and control
pregnancy.
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Mechanical Barrier Methods: In these methods, physical devices such as condoms, diaphragm
and cervical caps are used. These devices prevent the entry of sperm in the female genital tract
during copulation, thus acting as barrier between them.
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Chemical methods: In these methods, specific drugs are used by females, which are of two
types – oral pills and vaginal pills.
Oral pills contain hormones which stop the ovaries from releasing ovum into the fallopian tube.
These pills are also called oral contraceptives (OCs) which acts by changing the hormonal
balance of the body so that eggs are not released and fertilization cannot occur. The use of
Intrauterine Contraceptive Devices (IUCDs) prevents implantation in the uterus. This device is a
copper-T placed by safely inside the uterus by a doctor or nurse.
Surgical Methods: In these methods, a small portion of vas deferens in male and the fallopian
tube in female is surgically removed or tied. It is called vasectomy in males and tubectomy in
females. In this case, if the vas deferens in male blocked, sperm transfer will be prevented and if
the fallopian tube in the female is blocked, the egg will not be able to reach the uterus thus
fertilization will not take place.
Sex Ratio: It is the ratio of the number of females to the number of males in a population. The
female-male sex ratio must be maintained for a healthy society.
Question Answer
Q.1
What is the importance of DNA copying in reproduction ?
Ans. The importance of DNA copying : A basic event in reproduction is the creation of a DNA
copy. DNA copying is accompanied a cell division giving rise to two cells.DNA copying always involves
some variation. hence DNA copies generated are similar but not identical.
Q.2 Why is variation beneficial to the species but not necessarily for the individual ?
Ans. Organisms fill well defined places in the ecosystem with the help of reproduction. If some
variations are there in few individuals of these population. there could be chances for survival. For
example if there is a population of bacteria living in temperature increases due to global warming, most
of the bacteria will die. But the varients resistant to heat will survive and grow further. Variation is
important for survival .
Q.3 How does binary fission differ from multi fission?
Ans. In binary fission the nucleus first divides amitotically into two, followed by the division of
cytoplasm. The cell finally splits into two daughter cells.It occurs in during favourable condition.
Example; Amoeba, Paramecium.
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In multiple fission :, many individuals are formed from a single individual.
The nucleus of the cell divides repeatedly, producing many nuclei.
Each nucleus is surrounded by a small amount of cytoplasm and many daughter cells are
produced within the cyst.
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The cyst breaks up under favorable conditions and small off springs are liberated.
Example; Plasmodium
Q.4 How will an organism be benefited if it reproduces through spores ?
Ans. An organism will be benefited if it reproduces through spores because it is a simple & faster
method of reproduction . Spores are small & light ,to get dispersed via wind, water, animals. Spores
have thick covering to enable them to survive even in unfavourable condition.
Q.5 Can you think of reasons why more complex organisms cannot give rise to new individuals
through regeneration ?
Ans. More complex organisms cannot give rise to new individuals via regeneration because their
body is more complicated , have specific organ to reproduction, occurs division of labour in the body of
the organisms.
Q.6 Why is vegetative propagation practised for growing some types of plants ?
Ans. In vegetative propagation, new plants are obtained from the parts of old plants like stem,
roots and leaves, without the help of any reproductive organ. It is a cheaper ,easier method of plant
propagation. Seedless plant can be grown via vegetative propagation in aseptic condition( in lab., dark
plant culture room etc) .
Q.7 How is the process of pollination different from fertilization ?
Ans. In Pollination transfer of pollen grains from the anther of a stamen to the stigma of a carpel.
The pollen grains are transferred by many agents, such as insects (bees and butterflies), birds, man,
wind and water. fertilization in plants the fusion of pollen grains, nuclei & secondary nucleus of embryo
sac to form diploid zygote & triploid endosperm nucleus. Fertilization in animals the fusion of a male
gamete with a female gamete to form a zygote.
Q.8 What is the role of a seminal vesicles & the prostate gland ?
Ans. Seminal vesicles are a pair of thin-walled muscular elongated sac which secretes fluid for
nourishment of sperms. Prostate glands also produce fluid which is released in the urethra along with
secretion of seminal vesicle. The secretion of accessory glands together with sperms is called semen and
sperms move smoothly inside the vagina.
Q.9 What are the changes seen in girls at the time of puberty ?
Ans. Thick hair growth in armpits and genital areas between the thighs.
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Thinner hair on legs, arms and face.
Oily skin Breast size begins to increase.
Darkening of nipple skin.
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10 –- Sci – Ch-8 – How do organisms Reproduce
start of menstruation
Q.10 How does the embryo get nourishment inside the mother’s body ?
Ans. The embryo gets nourishment via the placenta. Placenta is a disc shaped tissue ,embedded
in the uterine wall. Placenta contain villi on the embryo’s side of the tissue. This tissue provides a
exchange of nutrients, oxygen to pass from the mother to the embryo & in this way embryo gets
nutrition.
Q.11 If a woman is using a Copper-T , will it help in protecting her from sexually transmitted
diseases ?
Ans. No, because the sexually transmitted diseases occur by the fluid to fluid contact & take place
in the vagina.
EXERCISES:
1) Asexual reproduction takes place through budding in;
a) Amoeba
b) Yeast
c) Plasmodium
d) Leishmania
Ans. b) Yeast
2) Which of the following is not a part of the female reproductive system in human beings ?
a) Ovary
b) Uterus
c) Vas deferens
d) Fallopian tube
Ans. c) vas deferens
3) The anther contains ;
a) Sepals
b) Ovules
c) Carpel
d) Pollen grains
Ans. d) Pollen grains
Q.4 What are the advantages of sexual reproduction over asexual reproduction ?
Ans. In asexual reproduction ; production of new organism from a single parent without the
involvement of sex cells or gametes. Thus genetic variation not occur or slow , asexual reproduction is
simple & fast process.
In sexual reproduction ; Fusion of two gametes male & female coming from the parents.
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Sexual reproduction promotes diversity of characters in the off springs.
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10 –- Sci – Ch-8 – How do organisms Reproduce
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It results in new combinations of genes brought together in the gamete and this reshuffling
increases genetic variation.
It plays a prominent role in the origin of new species.
The sexual mode of reproduction incorporates process of combining DNA from two different
individuals during reproduction.
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Q. 5 What are the functions performed by the testis in the human beings ?
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Ans. The function of testis is to produce sperm and male sex hormone called testosterone. The
scrotum provides the optimal temperature for formation of sperms.
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Q.6 Why does menstruation occur ?
Ans. Menstruation found in females only when the egg is not fertilized by the sperms. when the
egg is not fertilized so, the thick & soft uterus lining having a lot of blood capillaries in it is not
required , unfertilized ovum disintegrated within a day & the uterus lining also break down As
the uterus lining contain many blood capillaries , so when it shed, blood along with other tissues
is released. This comes out of the vagina in the form of bleeding.
Q. 7 Draw a labeled diagram of the longitudinal section of a flower ?
Ans.
Longitudinal section of a flower
Q. 8 What are the different methods of contraception ?
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10 –- Sci – Ch-8 – How do organisms Reproduce
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Ans. Mechanical Barrier Methods: In these methods, physical devices such as condoms,
diaphragm and cervical caps are used. These devices prevent the entry of sperm in the female
genital tract during copulation, thus acting as barrier between them.
Chemical methods: In these methods, specific drugs are used by females, which are of two
types – oral pills and vaginal pills.
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Oral pills contain hormones which stop the ovaries from releasing ovum into the fallopian tube.
These pills are also called oral contraceptives (OCs) which acts by changing the hormonal
balance of the body so that eggs are not released and fertilization cannot occur. The use of
Intrauterine Contraceptive Devices (IUCDs) prevents implantation in the uterus. This device is a
copper-T placed by safely inside the uterus by a doctor or nurse.
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Surgical Methods: In these methods, a small portion of vas deferens in male and the fallopian
tube in female is surgically removed or tied. It is called vasectomy in males and tubectomy in
females. In this case, if the vas deferens in male blocked, sperm transfer will be prevented and if
the fallopian tube in the female is blocked, the egg will not be able to reach the uterus thus
fertilization will not take place.
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Q. 9 How are the modes of reproduction different in unicellular & multicellular organisms ?
Ans. Unicellular organisms have only one cell in their body & there is no separate tissue for
reproduction. so they can reproduce by fission & budding process.
Multicellular organisms have many cells in their body & have separate system for reproduction .
so they can reproduce by sexual & asexual method.
Q.10 How does reproduction help in providing stability to the populations of species ?
Ans. Consistency of DNA copying during reproduction is important for maintenance of body
design that allow the organism to live in particular area. DNA copying provides stability to the
population of species. stability also attained by equalizing the birth & death ratio.
Q.11 What could be the reasons for adopting contraceptive methods ?
Ans. Protection from sexually transmitted diseases
Restricting the no. of children
Enjoying a good reproductive health
Controlling population
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