*CHAPTER - 8
HOW ORGANISMS
REPRODUCE
CLASS :- X
MADE BY :- MANAS MAHAJAN
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* Reproduction
1) Reproduction :-
is the process by which living organisms
produce new individuals of the same species.
Reproduction is necessary for the survival and increase
in the population of a species. If organisms do not
reproduce, their population decreases and species will
become extinct.
2) Do organisms create carbon copies of
themselves ?
The DNA (Deoxyribo nucleic acid) molecules in the
chromosomes in the nucleus is responsible for the transfer
of characters from the parents to the off springs. During
reproduction the reproductive cells produce two copies of
the DNA which separate into two cells. The DNA copies will
be similar but not identical to each other. So the new
individuals have slight variations from their parents. This is
the basis for variations and evolution of new species.
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* 3) The importance of variation :-
DNA copying during reproduction is important
for maintaining the body designs of different
organisms to survive in the existing environment.
But the environment is constantly changing due
to changes in temperature, climate, water levels
etc. If organisms cannot adjust themselves to the
changes in the environment then their species
will become extinct.
If there are variations in some individuals of a
species they may be able to survive the changes
in the environment.
So variations in species is necessary for the
survival of different species and for the evolution
of new species.
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* 4) Types of reproduction :-
There are two main types of reproduction in living
organisms. They are asexual reproduction and sexual
reproduction.
Asexual reproduction :- is reproduction in which new
individuals are produced from a single parent.
Sexual reproduction :- is reproduction in which two
individuals are involved to produce a new individual.
Asexual reproduction is of different types. They are:-
fission, budding, regeneration, fragmentation, spore
formation, vegetative propagation etc.
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*Fission
i) Fission :-
is an asexual reproduction by which a
unicellular organism divides and forms two or
more new individuals. Fission is of two types. They
are binary fission and multiple fission.
i) Binary fission :- In this method an organism
divides and forms two individuals. First the
nucleus divides and forms two nuclei. Then the
cytoplasm divides and forms two daughter cells.
Eg:- Amoeba, Paramaecium etc.
ii) Multiple fission :- In this method one organism
divides into many daughter cells. Eg.Plasmodium
(Malarial parasite).
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* ii) Budding :-
In this method a bud like projection is formed
on the body of the organism. The bud then
develops into a new
individual. It then separates from the parent and
forms an independent individual. Eg:- Hydra,
Yeast etc. bud
bud
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* iii) Regeneration :-
In this method a part of the body if the
organism if cut or broken can develop into a new
individual. Eg :- Hydra, Planaria, Star fish etc.
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* iv) Fragmentation :-
In this method the body of a simple
multicellular organism breaks up into smaller
pieces on maturation and each fragment
develops into new individuals.
Eg :- Spirogyra.
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* v) Spore formation :-
In this method structures called sporangia
produce tiny cells called spores. When the spores
come in contact with a moist surface, it develops
into new individuals.
Eg :- Rhizopus , Mucor, Penicillium etc.
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* vi) Vegetative propagation :-
In this method new plants are produced from the
vegetative parts of the plant like root, stem or leaf. Eg:-
from roots – dhalia, sweet potato,
from stem – potato, ginger, from leaf – bryophyllum,
begonia.
Plants produced by vegetative propagation produce
flowers and fruits earlier than those produced from seeds. It
also helps in the propagation of plants which do not produce
seeds like rose, jasmine banana etc.
Vegetative propagation can also be done artificially by
cutting, layering, grafting etc.
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* 5) Sexual reproduction in flowering plants :-
a) Reproductive parts of a flower :-
The stamen and pistil are the reproductive
parts of the flower. Stamen is the male
reproductive part. It produces pollen grains in
the anther which contains the male germ cell
(male gamete). Pistil is the female reproductive
part. It produces ovules in the ovary which
contain the female germ cell (female gamete).
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* b) Pollination :-
The transfer of pollen grains from the anther to
the stigma of a flower is called pollination. It takes
place by wind, water or insects. If the pollen
grains are transferred from the anther to the
stigma of the same flower it is self pollination and
if it is transferred from the anther of one flower to
the stigma of another flower it is cross pollination.
Pollination takes place by insects, wind, water etc.
Cross pollination
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Self pollination
* c) Fertilisation :-
After the pollen grain is
transferred to the stigma it
produces a pollen tube
which passes through the
style and enters the ovary
and ovule. In the ovule the
male germ cell (male
gamete) fuses with the
female germ cell (female
gamete) to form a zygote.
This process is called
fertilisation.
After fertilisation the
zygote divides several
times and forms the
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embryo which then
* 6) Reproduction in human beings :-
a) Male reproductive system :-
The male reproductive system consists of a pair of testes
which produces the male reproductive cells called sperms
and the hormone testosteron. It is contained in sac like
structures called scrotum. From each testis arises a tube
called vas deferens. It joins into the urethra. The urethra is
enclosed in a muscular organ called penis. It has an opening
called genital pore. The seminal vesicles and prostate
glands produce fluids which provide nutrition and help in
the movement of the sperms.
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* b) Female reproductive system :-
The female reproductive system consists of a pair of
ovaries which produces the female reproductive cells called
ova or eggs and the hormone oestrogen. Above the ovaries
are tubes called oviducts or fallopian tubes. The two
oviducts unite into a bag like structure called uterus. The
uterus has opening called vagina.
Human ovum (egg)
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* c) Fertilisation in human beings :-
During sexual intercourse the sperms from the male enters
into the vagina of the female. The sperms reaches the
oviduct. One sperm fuses with an egg and forms a zygote.
The zygote then gets implanted in the uterus. The zygote
then starts dividing to form an embryo. The embryo gets
nutrition from the mother’s blood through the placenta. The
development of the child takes nine months and then the
child is born.
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* d) Menstruation :-
The ovary produces one egg every month and
the uterus prepares to receive the fertilised egg.
Its wall becomes thick and spongy with blood
vessels for nourishing the embryo. If fertilisation
does not take place then the uterus wall breaks
and comes out of the vagina as blood and
mucous. This cycle takes place once every month
and is called menstruation.
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* 7) Reproductive health :-
a) Sexually transmitted diseases :- are diseases
transmitted through sexual contact. They may be
bacterial
infections like gonorrhoea and syphillis etc. or viral
infections like warts and HIV-AIDS.
b) Prevention of pregnancy ( Contraception ) :-
Pregnancy can be prevented by three main methods.
They are barrier methods chemical methods and surgical
methods.
i) Barrier methods consists of using condoms,
diaphragm,
cervical caps, Copper T etc.
ii) Chemical methods consists of taking drugs like oral
pills, vaginal pills etc.
iii) Surgical methods consists of removing or tying a
small
part of the vas deferens in males (Vasectomy).
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or fallopian tube in female (Tubectomy).
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