Download Class 10th CBSE how do organisms Reproduction

Class 10th CBSE how do organisms Reproduction
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Reproduction is biological process in which an organism gives rise to young one (offspring)
similar to itself.
Reproduction is necessary to increase the population and maintain the continuity of the
species
Organisms produce similar offspring:
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Organisms produce similar offspring that are similar to offspring but not exact copies of them.
The offspring have similar body structures and similar genetic blueprints (DNA) in their cells
Reproduction involves first making copy of its DNA and creating the cellular apparatus for the
new cell. A cell divides to reproduce two new similar cells. DNA carries information for making
proteins.
Any change or error in the copying of DNA cause variation in the offsprings.
Due to this tendency for variation, organisms do not create exact copies during reproduction.
The importance of variation
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Populations of organisms fill well defined places , or niches, in the ecosystem, using their
ability to reproduce.
The consistency of DNA copying during reproduction is important for the maintenance of body
design features that allow the organism to use that particular niche. Reproduction is therefore
linked to the stability of populations of species.
However niches can change because of reasons beyond the control of the organisms.
Temperatures on the earth can go up and down, water level can vary, or there could be
meteorite hits etc.
If a population of reproducing organisms were suited to a particular niche and if the niche were
drastically altered, the population could be wiped out.
However if some variations were to be present in a few individuals in these populations, there
could be some chance for them to servive.
Thus, if there were a population of bacteria living in temperate water and if the water
temperature were to be increased by global warming, most of these bacteria would die, but the
few variants resistant to heat would servive and grow further, variation is thus useful for the
survival of species over time.
Types of reproduction:
Two main types of reproduction are found in organisms : asexual and sexual.
Asexual reproduction
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In asexual reproduction an offspring is produced by a single parent without the process of
gamete(sex cell) formation. Asexual reproduction is common in single celled organisms of
plants and animals.
In this method certain body cells of the parent organism undergo repeated mitotic cell division
to form two or more new organisms of the same kind.
Examples: binary fission in amoeba, fragmentation in spirogyra, regeneration in planaria,
budding in hydra, spore formation in Rhizopus fungus, vegetative propagation in flowering
plants.
Characteristics of asexual reproduction:
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A single plant is involved
Gametes are not formed
No fertilization takes place
There is only mitotic cell division.
Daughter organisms are genetically identical to parent
Multiplication occurs rapidly
Types: asexual reproduction takes place in the following ways
1. Fission 2.budding 3. Spore formation
Vegetative propagation
4. Regeneration
5. Fragmentation 6.
Binary fission: in this process of asexual reproduction , the parent organism divides into two equal
halves, each half forming an independent daughter organism. binary fission involves mitosis. The
resultant offsprings are genetically identical to the parent and to each other. Eg. Amoeba, euglena,
paramecium, leishmania etc.
Amoeba reproduce by binary fission by dividing its body into two equal parts. This happens as
follows, when the amoeba cell has reached its maximum size of growth, then first the nucleus of
amoeba lengthens and divide into two equal parts. After that cytoplasm of amoeba divides into two
parts, one part around each nucleus. In this way one parent amoeba divides to form two smaller
ameobae called daughter amoeba and we say that one amoeba produce two amoeba. The two
daughter amoeba produced here grow to their full size by eating food and then divide again to
produce four amoeba
Multiple fission: in this the parent organism splits to form many new organism at the same time.
During multiple fission the nucleus of parent cell divides several times into many daughter nuclei.
Then the daughter nuclei get arranged along the periphery of the parent cell. Later the cytoplasm
divides into as many pieces as no. of nuclei. Each uninucleited piece develops an outer membrane.
Finally the parent cell divides into several uninucleate daughter individuals which behave as
independent organisms. This type of fission occurs in malarial parasite- plasmodium, in which about
1000 daughter cells are produced from one parent cell, each capable of invading a red blood cell.
Fragmentation:some multicellular organisms have simple body organization. These organisms are
comprised of a random collection of cells without differentiation of specialized tissues and organs.
Such organisms reproduce by breaking of their bodies into small pieces. Each of these piece is called
a fragment. These fragments grow into new individuals and the mode of reproduction is called
fragmentation. Eg. A green filamentous alga- spirogyra has a multicellular body with similar cells.
Each cell of spirogyra may divide and growth of the filament occurs simply by cell division. The
filament of spirogyra may break into small fragments and each fragment may grow into a new plant.
Regeneration: in certain organisms eg planarians new individuals can be regenerated from small
body fragments. This method is applied by certain organisms for asexual reproduction and
multiplication.
It may be defined as the ability of an organism to regenerate its lost parts of the bodywhich have been
removed, as by injury or autotomy (self amputation of body parts, eg some lizards can break off part
of the tail).
Regeneration is common in lower plants eg algae, fungi etc and animals hydra planaria and sponges.
A mature filament of spirogyra or hypha of Mucor (a fungi) breaks into two or more pieces and each
piece grows into a new individual. This method of reproduction in plants is called fragmentation.
Similarly if the body of hydra is cut into small pieces, even a fragment measuring 1/6 mm can
regenerate into an entire individual. Regeneration in planaria is shown in figure above.
Budding: formation of daughter individual from a small projection, the bud, arising on the parent body
is called budding. Thus, budding may be defined as the production of new individual from an
outgrowth of the parent individual.
Budding occurs in yeast, some protozoans and certain lower animals eg hydra. In multicellular
organisms like hydra, a bulging on the body appears as a result of repeated mitotic divisions in the
cells. It results in the formation of a lateral outgrowth called bud. The bud enlarges in size by further
divisions of the cells and attains the shape of parent to which it is attached. Finally , it separates from
the parent body and starts behaving as a new hydra.
Budding is the most common method of asexual reproduction in budding in yeast that take place
under favourable conditions(when it grows in sugar solution).during this process a small bud like
outgrowth appears at one end of the parent cell which gradually enlarges in size. The nucleus
enlarges and divides into two daughter nuclei. One daughter nucleus goes into the bud and the other
remains in the parent cell. Gradually the bud becomes almost of the same size as the parent cell.
Then constriction appears at the base of the bud and a separating wall is laid down. Sometimes a
bud may produce another bud over it which is still attached to parent cell forming a false mycelium.
Spore formation: this is a asexual method of reproduction . the reproduction by spore
formation takes place in plants. In spore formation, the parent plant produces hundreds of
microscopic reproductive units called spores. When the spore case of the plants burst, then
the spores spread into air. When these air-borne spores land on food or soil under favourable
conditions, they germinate and produce new plants.most of the fungi (like Rhizopus, mucor
etc.), bacteria and non flowering plants such as ferns and mosses reproduce by the method of
spore formation.
The common bread mould plant consists of fine , thread like projections called hyphae and thin
stem having knob like structures called sporangia. Each sporangium contains hundreds of
minute spores enclosed in spore case. When the spore case bursts, the tiny spores are
dispersed in air. These spores are asexual reproductive unit which can produce more bread
mould plants under favourable conditions.
Vegetative propagation:
The reproduction by vegetative propagation occurs only in plants. In vegetative propagation,
new plants are obtained from the parts of the old plants like stem, root, leaves without the help
of any reproductive organs.
Some most common natural methods of vegetative propagation in plants are:
i)
Modified tuberous root can be propagated vegetatively when planted in soil.(sweet
potato).
ii)
The buds present on the roots can grow into leafy shoots. (Guava)
iii)
Underground modified stems such as rhizomes (ginger) , corms (banana), bulbs (garlic
and onion) propagated vegetatively when planted in soil.
iv)
Some plants develop adventitious buds on their leaves which develop into new plants
(bryophyllum) .
v)
Money plant can be grown by vegetative propagation by using a piece of its stem.
Artificial propagation in plants:
1. Cutting: A small part of a plant which is removed by making a cut with a sharp knife is called
cutting. a small piece of a plant (stem, leaves, root) used for propagation. Stem cutting is most
commonly used. Eg. Grape, rose, sugarcane etc. in this method about 20-30 cm long pieces of
stem are planted in natural position in the wet soil. It gives off roots from lower end and shoot
buds from aerial nodes. A cutting develops a new plant, similar to the parent plant.
2. Layering: in this method a branch of the plant is pulled towards the ground and a part of it is
covered with soil leaving the tip of the branch exposed above the ground. After sometime, new
roots are developed from the part of the plant buried in the soil. The branch is then cut off from
the parent plant. The part of the branch which has developed roots grows to become a new
plant like parent plant. Jasmine plant propagated through this method.
3. Grafting: it is a method in which parts of two plants are joined in such a way that they grow as
one plant. Grafting is done between the two closely related dicot plant having vascular
cambia.the rooted plant in which grafting is performed is called the stock. The portion of other
plant that is grafted on to the stock is called scion. During grafting about 4-12 inches long
scion, with all the buds intact, is placed on the cut end of the stock and tied in such a way that
the cambium of the two come in contact with each other. The joint is covered with a layer of
wax or clay to prevent the evaporation of water or entry of pathogen. All the buds of stock must
be removed.
Tissue culture: this method includes propagation of plants by culturing the cells, tissues, organs. In
this method, the plant cells or tissues are cultured on a sterilized medium containing necessary
nutrients and hormones. A proper medium is important in plant tissue culture technique. The culturing
of cells or tissues result in the formation of an undifferentiated mass of cell called callus. Callus is fast
growing cellular mass, which is then transferred to another medium for differentiation of plantlets.the
plantlets are then transplanted to separate pots or nursery beds and allowed to grow for a definite
period of time. The matured plants are then transplanted in the fields. This method is employed for
quick multiplication of commercially important plants like orchids, dahlia, chrysanthemus etc.
Advantages of tissue culture:
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Tissue culture is a very fast technique. Thousands of plantlets can be produced in a few weeks
time from a small amount of plant tissue.
The new plants produced by tissue culture are disease free.
Tissue culture can grow plants round the year, irrespective of weather or season.
Very little space is needed for developing new plants by tissue culture.
Significance of asexual reproduction: although it is simple and fast, but since there is no variation, it
does not contribute to evolution of the species.
Sexual reproduction:
Sexual reproduction takes place by the combination of special reproductive cells called sex cells or
gamets.sex cells are of two types male sex cells (male gamets) and female sex cells (female gamet)
.it involves two major processes:
1. Formation of haploid cells, the gametes, by meiosis cell division.
2. Fusion of two gametes forming diploid cells, the zygote (fertilization).
Zygote then grows and develops into a new organism in due course of time.
Genetic basis and advantages of variation: it involves fusion of male and female gametes coming
from male and female organisms. Since fusing gametes come from two different and sexually distinct
individuals, the offsprings exhibit diversity of characters. And meiosis during gametogenesis provide
opportunity for new combination of genes. It plays a prominent role in the origin of new species and
leads to variation required for evolution.
Gamete formation , inside the gonads of diploid (2n) organisms, involves meiosis or reduction
division. The gamete mother cell is diploid (2n) ie it has two set of chromosomes. This single diploid
cell divides by meiosis to form 4 haploid(n) daughter cells. Each daughter cell become a gamete,
either male or female. Each gamete possesses single set of chromosomes. That means this division
involves copying of the DNA as well as cellular apparatus. There is a stage in such nuclear division
where crossing over of chromosomes takes place. This is important step which results a slight
different composition of chromosomes in gametes. Fusion of these gametes result in the formation of
slightly different individuals which show variations.
Sexual reproduction in flowering plants:
 The reproductive part of the flowering plant is the flower.
 Most flowers have both the male and female reproductive organs, but some bear either the
male or the female gametes. Such flowers are known as unisexual flowers (eg watermelon,
papaya, cucumber etc) . flowers with both sex organs are known as bisexual flowers. (hibiscus
, pea etc).
 The main parts of the flower are:
 Receptacles: it is the base of the flower to which all the parts of a flower are attached .
 Calyx or sepals: the green leaf like parts in the outermost circle of a flower are sepals.
All the sepals taken together are called calyx.
 Petals or corolla: petals are generally large, showy and brightly coloured to attract
insect pollinators. These are not directly involved in reproduction.
 Androecium: it is a collection of stamens, the male reproductive organs of flower.
Each stamen consists of anther and filament. The filament is a long stalk that bears
anther at the top. Anther contains pollen sacs. The pollen grains are made inside the
pollen sacs. Each pollen gain produce two male gametes.
 Gynosium or pistil : it is the collection of carpels female reproductive organs of flower.
Each carpel has swollen ovary, long style and terminal stigma. The stigma receives
pollen grains during pollination and support their growth. The style bear stigma in a
suitable position to receive pollen and also provides passage for the entry of pollen
tube. The ovary is swollen and hollow basal part that contains ovules. Each ovule has
an embryosac that bears a haploid egg- the female gamete.
In plants, the fusion of male and female gamete takes place inside the embryosac,
which is located inside the ovule. Fusion occurs only when the pollen grains are
transferred to the stigma of the same or another flower.
Pollination:
 The transfer of pollen grains from the anther to the stigma is called pollination.
 An external agent such as wind, water, animal, gravity or growth, contact is necessary for
effective pollination.
 Pollination is of two types: self- pollination, cross pollination
 The transfer of pollen to the stigma of the same flower is called self-pollination.
 Cross pollination is the transfer of pollen from the anthers of a flower to the stigma of the flower
on another plant of the same species.
 It occurs with the help of two main group of agents- biotic- insect, birds and abiotic- water and
air.
Fertilization: After a pollen grain falls on the stigma, the next step is fertilization. Fertilization occurs
when the male gamete present in pollen grain joins with the female gamete present in ovule.
This happens as follows: when the pollen grain falls on the stigma of the carpel, it burst open
and grows a pollen tube downwards through the style towards the female gamete in the ovary.
A male gamete moves down the pollen tube. The pollen tube enters the ovule in the ovary.
The tip of pollen tube burst open and male gamete comes out of pollen tube. In ovary, the
male and female gamete present in ovary to form fertilized egg called zygote.
Formation of fruit and seed: zygote divides several times to form an embryo within the ovule. The
ovule develops a tough coat around it and is gradually converted into a seed. The ovary of
flower develops and becomes a fruit with seed inside it. The other parts of the flower like
sepals, petals, stamens, stigma and style dry up and fall off. Only ovary is left behind. The
seed is the reproductive part of a plant. The seed contains a baby plant ie embryo and food for
the baby plant.the part of the plant in seed which develop into shoot with leaves is called
plumule and the part which develops into roots is called radicle. The part of the seed which
stores food for young plant is called cotyledon. The young plant present inside seed is in
inactive state, when the seed gets suitable conditions like water, air, warmth etc., it germinates
and new plant grows out of the seed.
Sexual reproduction in human beings:
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The age at which the sex hormones begin to be produced and the boy and girl becomes
sexually mature is called Puberty.
Generally boys attain puberty at the age of 13 to 14 years while girls reach puberty at an age
of 10 to 12 years.
On attaining puberty, the male gonads called testes start producing male gametes called
sperms and the female gonads called ovaries start producing female gametes called ova or
egg.
The various changes which occur in boys at puberty are:
 Hair grows under armpits and in public regions between the thighs.
 Body becomes more muscular due to development of muscles.
 The skin becomes oily and develop pimples.
 The voice deepens (crack).
 The penis and testes become larger.
 Testes start to make sperms.
The various changes which occur in girls at puberty are:
 Hair grows under armpit and public region.
 The skin becomes oily and develop pimples.
 Mammary glands develop and enlarge.
 Ovaries start to release eggs, menstruation start.
Male reproductive system:
 The male reproductive organs include the testes,scrotum,vas deferens,urethra, seminal
vesicles, penis and some associated glands such as the prostate gland.
 Testes: human male possesses two testes which are primary reproductive organs, lying
outside the abdominal cavity. The 2 testes are male gonads where sperms(male gametes) are
produced. The testes also produce the male sex hormone- testosterone.
 Scrotum: it is pouch of skin , it is divided into 2 sacs in which 2 testes lie. The scrotum acts as
thermo-regulator and provides optimal temperature for the formation of sperms. The sperm
develop at a temperature 1-3ºc lower than normal body temperature.
 Vas deferens: this is a straight tube about 40cm long also called sperm duct, which carries the
sperm into seminal vesicles. The sperms are temporarily stored in the seminal vesicles, where
mucus and watery alkaline fluid containing sugar- fructose mix with the sperm.
 Prostate gland: the sperm duct from both sides join near the base of urinary bladder, opening
into a single tube called urethra. Prostate glands pour their secretions into the seminal fluid.
The urethra leads outside the body through the organ called penis.it carries both urine as well
as seminal fluid along with sperm.
 Penis: it is muscular tubular organ made up of erectile tissue . it forms common passage for
both urine and sperms. On being stimulated the erectile tissue filled with blood, making the
penis erect and firm, so that it may be inserted into the vagina of the female to pass on the
sperms.
Female reproductive system:
It includes ovaries, fallopian tube, uterus, vagina.
 Vagina: the ovaries are a pair of small, oval organs in the lower part of the abdominal cavity.
They produce female germ cells- eggs/ ova. They also secretes female sex hormonesestrogen and progesterone. Every 28 days, one of the ovaries releases an ovum.
 Fallopian tube: also called oviduct, are pair of thin tubes that lead from ovaries to the uterus.
Each fallopian tube has a funnel-shaped opening near the ovary.it carries ovum from ovary to
uterus and also provides the appropriate environment for its fertilization.
 Uterus: it is a large inverted pear shaped, muscular structure that lies behind the bladder . if
fertilization takes place, the embryo gets attached to the wall of uterus and grows there until
birth.
 Vagina: the uterus opens into vagina through the cervix. Vagina is a muscular tube whise
walls contain elastic tissue.it is well adapted to receive the male’s penis during copulation. It is
called as birth canal as it allows passage of the baby at the time of child birth.
Sexual cycle in females:
 In human females , the ovaries start releasing ovum once every 28 days from the age of
puberty. The release of an ovum from an ovary is called ovulation, it takes place always after
28 days.
 Before every ovulation, the inner lining of the uterus becomes thick and soft with lot of blood
capillaries in it. These changes in the uterus is necessary because in case the ovum released
by the ovary gets fertilized by the sperm, then the uterus has to keep this fertilized ovum for
further development so that it can grow into a baby in due course of time.
 If sperm is not available at the time of ovulation, the ovum fertilization does not take place.
Thus unfertilized egg dies within a day and the uterus lining also breaks down, since the uterus
lining contains lot of blood vessels, so the breaking of uterus lining produces blood along with
other tissues .the blood and other tissues come out of the vagina in the form of bleeding. This
process is called as menstruation.
 This cycle gets repeated after every 28 days due to non fertilization.this cycle is controlled by
hormone estrogen.
 Menstruation stops temporarily when the ovum gets fertlised and woman gets pregnant. It
restarts after the birth of child.
 Menarche and menopause: at puberty the commencement of menstruation is called as
menarche. Cessation of cycle of events in ovary and uterus around the age of 50 years and
stoppage of menstrual flow is called menopause.
fertilization : when semen is discharged in the vagina during sexual intercourse, the sperm begin
moving up the vagina and uterus, finally reaching the fallopian tube. But usually only one sperm fuses
with the ovum. The sperm can remain alive for about 12 hrs. in this span of time, if it meets the ovum,
it is likely to enter the ovum. This is called fertilization.
Post fertilization changes:
 Implantation: the fertilized egg (zygote) moves down the fallopian tube and continuously
undergoes cell division to form embryo. The embryo gets embedded in the wall of the uterus.
This process is called implantation.
 The developing embryo at first derives nourishment directly from mother’s blood flowing in the
vessel lining the uterus wall. In about 3 weeks, it starts absorbing food and oxygen through an
organ calledplacenta. The embryo is connected to the placenta by a tube called umbilical
cord.
 By 8 weeks the embryo starts showing human features and is referred as Foetus. The total
period of embryonic development , from the time of fertilization to birth is called gestation
period. It is around 280 days or 9 months in humans.
 The wall of the uterus develops a thick layer of muscles during pregnancy. At the time of the
birth, uterine muscles contract rhythmically ,and finally baby is expelled out by the contraction
of uterine muscles is termed as Parturition.
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Birth control:
The prevention of pregnancy in women is called contraception. Various ways of contraception:
Mechanical barrier method: in these methods physical devices such as condom, 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 method: in these methods special pills are used by females, which are of two typesoral pills and vaginal pills.oral pills contains hormones which stops the ovaries from releasing
egg into oviduct, thus fertilization cannot occure.
IUCD (intra uterine contraceptive device): devices such as copper-T made of metal or plastic
are placed inside the uterus by a doctor to prevent implantation process.
Surgical methods: in these methods small portion of vas deferens (in males) and fallopian
tube (in females) surgically removed and tied with thread. This is called vasectomy in males
and tubectomy in females. This is permanent method of contraception.
Reproductive health: is all those aspect of general health which help a person to lead a normal, safe
and satisfying reproductive life.
Sexually transmitted diseases (STD): these are the diseases which are spread by sexual contact
from an infected person to a healthy person. They are caused by various microorganisms.some of
these examples are:
1. Gonorrhoea: it is caused by bacteria. It is characterised by inflammation in urino genital tract
and the patient feels burning sensation during urination. This bacteria infects ureter in male
and cervix in females.
2. Syphilis: it is caused by bacteria. It is characterised by lesions in mucous membrane of
urinogenetal tract and ulcers .
3. AIDS (Acquired immunodeficiency syndrom): it is caused by virus called HIV (human
immunodeficiency virus). Which suppresses the bodies immune mechanism and thereby
susceptible to ant disease.
Mode of transmission of AIDS:
1. By having sexual contact with the infected person
2. By the transfusion of blood of infected person
3. Through infected needles used for injections.
4. Through infected mother to child during pregnancy.