Asexual Reproduction

Asexual reproduction is a process resulting in the production of genetically

identical offspring from one parent.
• It does not involve gametes or sex cells & also does not require
fertilization.
• The organisms produced are genetically identical to the parent & to

ra
each other.

Mi y
Examples of Asexual Reproduction

b
sh
➢ Bacteria divide into two identical cells by binary fission which is
simple cell division.
ah led
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ul
Dr om

➢ Fungi:
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They reproduce by spore formation.

In penicillium: The hyphae (long
filamentous structures which form the
body) collectively known as the mycelium
develop vertical hyphae which produce
chains of spores at their tips. They are
dispersed by air.
Asexual Reproduction

In Mucor: It is similar to the Penicillium

fungus but the vertical hyphae develop spherical
structures known as sporangia which contains
hundreds of spores. They are dispersed by rain or
insects.

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Mi y
b
sh
ah led
Asexual Reproduction in Flowering Plants
➢ Bryophyllum: It reproduces
by special buds which
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develop in their leaf

margins. These buds fall off
ul
& produce new plants.
Dr om
C

➢ Stolon (Runners): They are horizontal stems that grow just above
the ground. They grow from the main shoot & usually have long
internodes (the area between two nodes). At each node, buds are
present which can give rise to both shoot & root and thus to new a
Asexual Reproduction

plant. The main

plant initially
provides the
nutrition to the
new plants &
then the stolon
withers leaving
behind new
plants. Eg.

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strawberry

b
sh
ah led
➢ Rhizomes: These are horizontal
stems which develop under the
ground. Buds are produced at
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the nodes which may give rise

to a new plant producing both
ul
shoot & roots. Eg. Ginger.
Dr om
C

➢ Bulbs: The stem is vey short in

these plants & is surrounded by
thick, fleshy leaves which store
food. This stored food is used
by the plant for the growth of
the main terminal bud which
produces a flowering stalk &
some leaves. The leaves
prepare food which is sent to
the leaf bases the lateral buds
which arise from the stalk.
These lateral buds may form new plants later. Eg. Daffodil,onion.
Asexual Reproduction

➢ Tubers: Tubers are swollen portions of an underground stem that

store food
so a plant
can lie
dormant
over the
winter, for
example,
potatoes.

ra
Mi y
Axillary
buds, commonly known as ‘eyes’, form over the surface of the tuber

b
and produce shoots that grow into a new plant the following year.

sh
ah led
Asexual Reproduction in Animals
➢ In Hydra: Hydra reproduces asexually
by a peculiar process called budding-
Certain projections from the body
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wall appear. They are known as

‘buds” which later break away to
ul
form a new adult.
Dr om
C
Asexual Reproduction

Advantages & Disadvantages of Asexual reproduction

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b
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Dr om
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Sexual Reproduction in Plants

SEXUAL REPRODUCTION IN PLANTS

SEXUAL REPRODUCTION: It involves the fusion of the male gamete and the
female gamete to form a zygote and the production of offspring that are
genetically different from each other.
• The body cells have two sets of chromosomes arranged in pairs present
in their nucleus.eg. Humans have 46 chromosomes arranged in two sets
of 23. A cell having both the sets i.e. 46 chromosomes is known as
diploid.

ra
• Gametes differ from normal cells in their chromosome number. They

Mi y
have a single set of 23 chromosomes and are known as haploid.

b
• On fusion of the gametes→ a zygote having both the sets of

sh
chromosomes i.e. 46 chromosomes is formed. Thus, the zygote is diploid
& the chromosome number is maintained in the species.
ah led
Advantages of Sexual Reproduction
1. In sexual reproduction: the gametes maybe produced by different
plants of the same species giving rise to certain variations which may
be beneficial like increased fruit size or a greater number of seeds.
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2. It may lead to development of characters which may help the plants to

ul
adapt to new environments.
Dr om

3. It may give rise to a disease resistant species.

Disadvantages of Sexual Reproduction
1. It may require more time as more than one plant is usually required for
the process.
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2. It may be difficult for a species in a far-flung area to reproduce.

FERTILIZATION: It is defined as the fusion of the nuclei of the two gametes.

Male Organs of Flowering Plants: Stamens (producing pollen grains)
Female Organs of Flowering Plants: Carpels (It becomes the fruit and contains
seeds)
HERMAPHRODITE (BISEXUAL): Most plants have both the male and female
structures present in the flowers. Such flowers are known as hermaphrodite or
bisexual.
Sexual Reproduction in Plants

Parts of a Typical Flower

1. Sepals: They
are the
outermost
ring of the
flower. They
are usually

ra
leaf like

Mi y
green in

b
colour and

sh
protect the
flower when
ah led
it is in the
bud stage.
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ul
2. Petals: They are brightly coloured and may be scented. They may range
Dr om

from 3 to 10
in most plant
species. In
some cases,
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they may be
joined in the
form of a tube
(eg. Daffodil) .
Their main
function is to
attract insects
with the help
of their colour
and scent for
the purpose of pollination. The petals of some plant species may have
fine lines running from top to bottom which are known as Guide Lines
Sexual Reproduction in Plants

which guide the insects towards the base of the petal where glands
known as nectary may be present. They secrete a sweet liquid called
nectar for the insects to feed on.

3. Stamens: It is the male reproductive part

of the flower. Each stamen is made up of
a long filament and an anther at its tip.

ra
Each anther has 4 pollen sacs which

Mi y
contain the pollen grains. The stamens

b
may be many, same or double as the

sh
number of petals/sepals.
ah led
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4. Carpels : These are the female

ul
reproductive parts of the flower. Some
Dr om

flowers may have many carpels (

blackberry) while others may have a
single carpel ( lupin). A typical carpel is
made up of : an ovary with a style on its
top and a platform like stigma at the tip
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for capturing the pollen grains.An ovary

contains one or many ovules. The ovules
contain the female gametes which form
the seed after fertilization and the ovary
becomes the fruit.
Sexual Reproduction in Plants

POLLINATION
The transfer of pollen grains from the anther (male part) to the stigma
(female part) of the plant. This transfer may take place within the same
flower (self-pollination) or from one flower to another of the same species
(cross- pollination). It usually takes place with the help of insects ( eg. lupin
and wallflower) or by wind (grasses and cereals).

Difference between Insect and Wind Pollination

ra
Mi y
Insect Pollinated Flowers Wind Pollinated Flowers

b
1. Petals –Large, brightly coloured with Petals- Small, green, inconspicuous and

sh
guide lines and usually scented. may be absent and are non-scented.
2. Nectaries-are usually present which Nectaries-are usually absent.
ah led
produce sweet nectar.
3. Anthers-are present inside flowers Anthers-have long filaments so that
so that insects have to brush past them they can hang outside the flowers so
to reach the nectar. that they are exposed to wind.
4. Stigmas-are small and inside the Stigmas-are large and feathery and
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flower. exposed outside so that they can catch

the pollen grains.
ul
1. Pollen grains-are produced in Pollen grains-are produced in large
Dr om

small numbers and are sticky or numbers and are small and light so
covered in spikes so that they that they can be blown in the wind.
can easily stick to the bodies of
the insects.
2. Bracts which are a type of Bracts are usually present.
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modified leaves are absent.

Certain Interesting Facts:

 Flowers such as the honeysuckle, with narrow, deep petal tubes, are
likely to be
pollinated only by moths or butterflies, whose long ‘tongues’ can reach
down the tube to the nectar.
 Tube-like flowers such as foxgloves need to be visited by fairly large
insects to effect pollination. The petal tube is often lined with dense
Sexual Reproduction in Plants

hairs, which impede small insects that would take the nectar without
pollinating the flower. A large bumble-bee, however, pushing into the
petal tube, is forced to rub against the anthers and stigma.

Self-pollination is the transfer of pollen grains from the anther of a flower to

the stigma of the same flower, or a different flower on the same plant. Eg
peanuts
Cross-pollination is the transfer of pollen grains from the anther of a flower

ra
Mi y
to the stigma of a flower on a different plant of the same species.Eg grasses,
apples

b
sh
ah led
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ul
Dr om
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Sexual Reproduction in Plants

Fertilisation
After pollination, if the pollen grain has landed on
the stigma of the same or another flower of the same species, the plant
starts preparing for the process of fertilization with the following steps:
 A pollen tube starts developing from the
grain on the stigma. It grows down the
style and acts as a passage for the male
gamete to reach the female gamete in the

ra
ovule.

Mi y
 The ovule has several layers of cells around

b
it known as integuments. There is a small

sh
gap at the end of the integuments known
as the micropyle through which the pollen
ah led
tube enters the ovule.
 The male gamete (pollen nucleus) travels
via the pollen tube into the ovule and fuses
with the female gamete (ovule nucleus) to
form a zygote. This completes the process
. R pi

of fertilisation.
ul
 A single pollen grain can fertilise a single
Dr om

ovule.If the flower has many ovules in the

ovary then many pollen grains will be
required to fertilise all of them.
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Development of Fruit and Seed

After completion of fertilization:
 The sepals and petals may shrink and fall off.
 The stamens, style and stigma wither away.
 The ovary wall may become soft and fleshy (plum), dry and hard
(Brazilian Nut) or a leathery pouch (wallflower).
 The fertilized ovule forms the seed with the zygote developing
into an embryo after cell division (Mitosis). The integuments of
the ovule become hard and dry to form the testa or the seed
coat.
Sexual Reproduction in Plants

 The food for the developing embryo may be provided by

specialized seed leaves called cotyledons-There is one cotyledon
in Monocotyledonous plants such as grasses or two cotyledons
in Dicotyledonous plants such as bean and pea.
 Endosperm is a specialized food storing tissue found in the
seeds. It provides food for the developing embryo especially in
Monocot plants such wheat.
 The fertilized ovary which has grown larger is known as the
fruit.

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Mi y
b
sh
ah led
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ul
Dr om
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Germination

It is the process or mechanism by which seeds develop into a new plant.

It takes place usually when certain conditions are favourable like:
 Sufficient moisture (Not Excess water)
 Optimum Temperature (so that the plant enzymes can be
activated)
 Availability Of Oxygen (so that aerobic respiration can take place)
 Some seeds may also require specific conditions such as light (
e.g. lettuce)
Sexual Reproduction in Plants

ra
Mi y
b
sh
ah led
Types of Germination:
Epigeal- This is a type of germination in which the cotyledons are carried
above the ground by the growing plant due to elongation of the hypocotyl
(region between the cotyledon and the radicle). It is seen in dicot plants like
. R pi

sunflower, bean and castor.

ul
Hypogeal- This is a type of germination in which the cotyledons remain
Dr om

below the ground inside the soil during the growth of the plant due to
elongation of the epicotyl (region above the cotyledons). It is seen in monocot
plants like maize, wheat and also in certain dicot plants like gram, pea.
C

Dormancy: It is a condition where seeds do not germinate or are said to

be in a resting state irrespective of the external conditions. It is a phase which
occurs usually to tide over unsuitable environment for the growth of a new
plant. The main factor which aids dormancy is the low water content of the
seeds.
Sexual Reproduction in Plants

Process of Germination
The seed first absorbs water through the micropyle.
The cotyledons swell up and the seed coat (testa) bursts open.
As water is absorbed by the cotyledons, the enzymes get
activated:
Insoluble starch is converted to maltose ( By enzyme - Amylase)
Protein is split into amino acids ( By Proteases)

ra
Mi y
b
sh
ah led
They dissolve in water and are passed on to the growing plant
for providing nutrition via diffusion.
Usually, the radicle (which is the embryonic root) starts
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developing first and starts growing down into the soil. Lateral
roots (which are branches of the main root) develop later.
ul
Soon, very fine root hairs appear on both the roots and are
Dr om

responsible for absorbing water and salts for the growing plant.
The plumule (which is the embryonic shoot) starts growing
upwards.
(The cotyledons may be pulled above the soil (EPIGEAL GERMINATION E.G.
C

BEAN) or they may remain underground (HYPOGEAL GERMINATION E.G. PEA)

All the food for the growing plant is provided by the cotyledons
The cotyledons soon shrink and fall off as their stored food is all
used up. The plumule leaves now take up the job of food
preparation of the plant.
Sexual Reproduction in Plants

Experiments To Prove the Requirements For Germination

ra
Mi y
b
sh
ah led
The seeds in B will germinate normally. Those in A will not
germinate. The seeds in C may have started to germinate but will
probably not be as advanced as those in B and may have died
and started to decay.
. R pi

Interpretation: Although water is necessary for germination, too much of it

may prevent germination by cutting down the oxygen supply to
ul
the seed.
Dr om

Uses of Water In a Germinating Seed

1. Activation of enzymes present in the seed.
2. Conversion of insoluble starch and protein to soluble forms so that they
can be utilized.
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3. Transport of materials to the growing parts.

4. It helps in increasing the size of the vacuoles present in the cells so that
there is overall growth of the plant.
5. Maintenance of turgor pressure so that the stem stays erect and the
leaves remain wide open.
6. Provide water needed for photosynthesis once the leaves of the new
plant take over.
7. Transport of nutrients from the soil to the growing parts of the plant.
Sexual Reproduction in Plants

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Mi y
b
sh
Result
The seeds in flask B will germinate but there will be little or no
ah led
germination in flask A.
Interpretation
The main difference between flasks A and B is that A lacks
oxygen. Since the seeds in this flask have not germinated, it looks
as if oxygen is needed for germination.
. R pi

To show that the chemicals in flask A had not killed the seeds,
ul
the cotton wool can be swapped from A to B. The seeds from A
Dr om

will now germinate.

Note: Sodium hydroxide absorbs carbon dioxide from the air. The
mixture (sodium hydroxide + pyrogallic acid) in flask A, therefore,
absorbs both carbon dioxide and oxygen from the air in this flask.
In the control flask B, the sodium hydroxide absorbs carbon dioxide
C

but not oxygen. If the seeds in B germinate, it shows that lack of

carbon dioxide did not affect them, whereas lack of oxygen did.
Sexual Reproduction in Plants

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Mi y
b
sh
ah led
Result
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The seedlings kept at 30°C will be more advanced than those at

room temperature. The grains in the refrigerator may not have
ul
started to germinate at all.
Dr om

Interpretation
Seeds will not germinate below a certain temperature. The
higher the temperature, the faster the germination, at least up
to 35–40°C
C
Reproduction In Humans

• Reproduction is the process by which new individuals of the species

are produced.
• In humans, the specialized cells responsible for reproduction are the
gametes: Males produce the male gamete known as sperm or
spermatozoa.
Females produce the female gamete known as the ovum or egg.
The Male Reproductive System

ra
Mi y
• The sperm are
produced in

b
specialized oval

sh
shaped organs
known as testes
ah led
(singular: testis)
which are two in
number. The
testis also
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produce the
male hormone:
ul
testosterone.
Dr om

• The testes lie

outside the body in a sac like structure called the scrotum.
This helps them
to be at a lower
C

temperature
than that inside
the body. This
temperature is
ideal for sperm
production.
• The main mass of
testis is
composed of
sperm producing
tubules which
join to form a
Reproduction In Humans

coiled tube outside the testis. This tube finally opens into a wider tube
known as the sperm duct.
• The two sperm ducts open into the urethra just below the urinary
bladder and pass through the prostate gland.
• The prostate gland & other glands secrete fluids in which the sperms
swim. The fluid contains glucose & mucus which provides nourishment
to the sperms as well as energy for their movement by respiration.
• The fluids from the prostate and other glands along with the sperm
constitute the semen.

ra
The urethra can pass both urine as well as semen but it does so only

Mi y
•
one at a time.

b
• The urethra passes downwards through the centre of the penis which

sh
contains the erectile tissue which helps in the deposition of sperm in
the female reproductive tract.
ah led
The Female Reproductive System
. R pi
ul
Dr om
C

• The eggs or ova are produced in specialized female reproductive

organs called: Ovaries (Ovary: singular). They are two in number & also
produce the female hormones- oestrogen & progesterone.
Reproduction In Humans

• The ovaries are solid, oval structures about 2-4 cm in length situated in
the abdomen, just below the kidneys. Usually, it releases a single egg
per month.
• The oviducts or fallopian tubes are the
tubes through which the ovum passes
after being released from the ovary. The
opening of the tube is funnel shaped and
it lies very close to the ovaries but does
not touch it.

ra
The oviducts are provided with ciliated

Mi y
cells which help in the movement of the

b
ovum down the tube towards the womb.

sh
• Uterus or the womb is the place where the
development of the offspring or baby
ah led
takes place. It is much wider than the oviducts & has thick, muscular
walls.
• Cervix or ‘the neck of the uterus’ forms the lower end of the uterus and
is formed by a ring of muscles guarding the narrow opening.
. R pi

• Vagina is a muscular tube which continues from the cervix to outside

the body. It is here that the sperms are deposited.
ul
• The urethra opens to the exterior through a separate opening just
Dr om

above the vagina.

C
Reproduction In Humans

Development of Male gametes (Sperm)

• The male gametes or sperms are formed in the tubules of the testis.
The walls of the tubules consist of fast dividing cells which after
repeated cell divisions develop a tail like structure known as flagellum
(plural: flagella). The cells are now known as sperms.
• The sperms than travel to the tube-like epididymis where they mature
& are stored.
• The prostate gland and other accessory glands secrete mucus rich
nourishing fluid which also helps in the movement of the sperm. The

ra
Mi y
sperm along with the fluid is known as semen.
• During mating, the contraction of the coiled tubes outside the testes

b
propels the sperms out of the urethra.

sh
• Sperm production starts in males at the onset of puberty.
ah led
• Millions of sperms are produced daily by the males after puberty.
. R pi
ul
Dr om
C
Reproduction In Humans

Development of Female Gametes or Ovum

• The egg cells or ovum are present in the female in the ovaries in a state
of arrested development since birth.
• After the onset of puberty, the eggs start to mature and are released
usually one at a time every four weeks from alternate ovaries.
• During maturation, the cells around the eggs divide & produce a fluid
filled sac like structure enclosing the egg known as the Follicle.
• On maturation, the follicle travels up to the surface of the ovary from
its deeper tissues & causes a slight bulging of the ovarian wall. The

ra
Mi y
follicle then ruptures releasing the egg which is then taken up by the
funnel end of the oviduct. This is known as ovulation. The egg then

b
travels down the oviduct by the movement of the cilia (hair like

sh
projections) present in the oviducts.
ah led
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ul
Dr om
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Reproduction In Humans

Structure of the sperm

• Sperms are much smaller than eggs or ovum and are produced in very
large quantities.
• It consists of a head, neck, middle piece & a tail or flagellum.
• The head has a cap like structure known as acrosome which
contains enzymes which help in dissolving the jelly coat of the egg
before fertilization so that he sperm nucleus can reach the egg
Adaptations

ra
nucleus. The head also contains the haploid sperm nucleus.

Mi y
• The middle piece has numerous mitochondria which provide energy

b
for the movement of the sperm by respiration.

sh
• The flagellum or tail helps in the movement of the sperm through
its whiplash like movement.
ah led
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ul
Dr om
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Reproduction In Humans

Structure of the Egg or Ovum

• The egg or the ova are round cells which are non-motile. They are much
larger than sperms.
• Usually only one egg is released every month after puberty by the ovaries
(alternately) during the fertile period of the female.
• The egg is surrounded by a jelly coat which protects the cell &
also prevents the entry of more than one sperm.
• There is abundant cytoplasm in the cell which has proteins &
Adaptations
fats. They are required for energy and nourishment if fertilization

ra
Mi y
occurs.
• There is a central haploid nucleus.

b
sh
ah led
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ul
Dr om

Difference between Sperm & Egg

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Sperm Ovum
1. They are very small ( 1. They are large cells
45µm) (0.2mm)
2. It has many adaptations 2. It has fewer adaptations
like acrosome, flagellum, like jelly coat.
many mitochondria.
3. It is highly motile. 3. It is non motile.

4. It is produced daily in huge 4. Usually only one egg is

quantities (more than released per month.
million)
Reproduction In Humans

Process of Fertilisation
Fertlisation: It is the process of
fusion of the male
nucleus(haploid) of the sperm
with female nucleus(haploid) of
the ovum resulting in the
formation of a diploid
zygote.This zygote develops into
an embryo by undergoing

ra
Mi y
repeated cell division.

b
sh
• During mating: sperms are deposited from the penis of the male into
the vagina of the female.
ah led
• The sperms then swim up into the cervix, then the uterus & finally
enter the oviduct with the help of their flagella using the energy
released by the mitochondria by respiration. The speed of the sperms
is about 4-5 mm per minute so they take some time before reaching
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the oviduct.
• Oviduct (fallopian tube) is the site of fertilization.
ul
Dr om

Millions of sperms are deposited in the

vagina but only a few hundred reach the
correct oviduct & ultimately only one of
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them can fertilize the egg. !!

Reproduction In Humans

• When a sperm comes in contact with an egg, the acrosome releases its
enzymes →
the jelly coat
surrounding
the egg is
digested→
The flagellum
of the sperm
is left outside

ra
& the head

Mi y
portion

b
containing

sh
the nucleus
fuses with the
ah led
egg cell membrane→ the sperm nucleus finally fuses with the egg
nucleus to from the diploid zygote. (This is the step where fertilisation
takes place.)
. R pi

The egg after ovulation can survive in

ul
the female oviduct for about 24 hours.
Dr om

The sperm can survive in the woman’s

body for around 5 days.
There exists only a short window period
of 4-5 days every month when
fertilisation can take place.
C

• The diploid zygote undergoes

repeated cell division to form a ball
of cells known as the early embryo.
Reproduction In Humans

Implantation
• The early embryo formed by cycles of cell division inside the zygote
travels down slowly through the oviduct towards the uterus with the
help of the ciliated cells of the oviduct.
• The cell divisions continue but their rate slows down.
• The uterus whose walls have become thick & spongy in anticipation of
fertilization is ready to receive the developing embryo.
• The embryo when it reaches the uterus: It sinks into the lining of the
uterine wall. This process is known as implantation. Implantation

ra
Mi y
takes place around 6-9 days after fertilization.
• The embryo now starts deriving nutrients & oxygen from the blood

b
vessels present in the uterine wall by diffusion. The waste products

sh
along with carbon dioxide diffuse out similarly.
ah led
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ul
Dr om
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Reproduction In Humans

Pregnancy
• Pregnancy is the time period between fertilization & birth of the
offspring. In Humans it is: 9 months. This period is known as the
gestational period. (Gestation period)
• The embryo
continues to grow
after implantation→
Most of the cells
start organ

ra
Mi y
formation while a
section of cells

b
grows projections

sh
into the soft tissue of the uterine wall giving rise to an irregular disc
shaped organ known as placenta- which acts as the connection
ah led
between the mother & the developing embryo.
• The placenta is attached to the
embryo by a tube-like umbilical
cord.
. R pi

• The organ development of the

embryo is complete within 8-12
ul
weeks of pregnancy- One of the
Dr om

first organs to form is the

heart.
• The embryo with all the formed
organs & the developed
C

placenta is now known as the

foetus.
• The uterus enlarges along with the
growing foetus. The foetus
becomes encased by a fluid filled membranous sac known as the amniotic
sac which is filled with a fluid known as amniotic fluid.
→The amniotic sac & fluid protect the foetus from mechanical injury and
unequal pressures.
→ The amniotic fluid also provides a media where the foetus floats freely
& can move its developing arms & legs so that there is proper bone &
muscle formation.
Reproduction In Humans

The Placenta
Placenta is a
unique organ
which has both
maternal &
foetal
components. It
is temporary in
nature and

ra
Mi y
forms the
connecting link

b
between the

sh
mother & the
developing foetus.
ah led
• It is connected to the foetus by a tube-like umbilical cord.
• The umbilical cord has two umbilical arteries which carry
DEOXYGENATED BLOOD from the foetus to the placenta & one
umbilical vein which carries OXYGENATED BLOOD from the placenta
. R pi

to the foetus.
ul
• The placenta has numerous finger-like projections called villi in the
Dr om

wall of the uterus which contains the capillaries arising from the
blood vessels of the foetus. The villi are in close contact with the
maternal blood vessels.
Functions:
C

• The maternal
blood vessels
in the uterine
wall lie very
close to the
placental
blood vessels
so oxygen &
nutrients like
glucose,
amino acids
can easily diffuse in to the blood vessels supplying the foetus
Reproduction In Humans

from the mother’s blood. (It must be noted that the maternal &
foetal blood never mix but remain separated by thin
membranes- This protects the delicate blood vessels of the
foetus from the high pressure which exists in the mother’s
vessels. It also prevents the formation of antibodies which may
harm the foetus if the blood groups of the mother & foetus are
different.)
• The placenta also allows the wastes generated in the foetus like
carbon-dioxide & urea to diffuse out to the mother’s blood for

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excretion.

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• Placenta prevents the entry of various harmful substances &

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pathogens into the foetal blood and thus protects the foetus.

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• Placenta allows protective antibodies from the mother’s blood
(Passive Immunity) to enter the foetal circulation. This provides
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temporary immunity to the baby especially after birth when its
immune system is under development.
Adaptations of Placenta:
1. The villi of the placenta provide a large surface area for diffusion to
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occur efficiently.
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2. The thin walls of the placenta allow diffusion to occur at a fast rate.
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3. There is a rich supply of maternal blood vessels to maintain the

concentration gradient.

• Certain toxic substances though can cross the placental barrier & affect the
foetus: Alcohol & Nicotine → they can cause low birth weight of the baby & in
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some cases even death.

• Viruses like HIV & rubella can cross the placenta & infect the foetus if they are
present in the mother’s blood. (Rubella or German measles is a mild disease in
adults but it can cause a wide variety of conditions in the baby like heart
disease, deafness, mental retardation etc. HIV being a disease of the immune
system can make the baby susceptible to all kinds of infections & may be fatal
even.
Reproduction In Humans

Birth of the Baby

• The foetus attains maturity in 9 months or 36 weeks.
• Contractions of the uterine wall start due to a signal from the brain
(which causes the release of a hormone)
• Amniotic sac ruptures along with the release of the amniotic fluid
through the vagina.
• Cervix widens or dilates.
• Baby passes out of the body of the mother through the vagina.

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Sexual Hormones
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• Puberty: It is a stage of physical development where the child starts
maturing into an adult. The sexual organs undergo maturation &
varying changes occur in the body. These are brought about by
hormones especially sex hormones like oestrogen & testosterone. In
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girls→ It occurs around 10- 14 years of age. In boys → It occurs around

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the same age or 1-2 years later.
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• Adolescence: It is the entire transition phase from the onset of puberty

to the attainment of adulthood by the child. It refers more to the
psychological aspect of the child than the physical.

The ovaries of the female contain all the ovum in a state of arrested
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development but they do not start maturation & release before the
onset of puberty.
The sperm production in males does not start before puberty.
Reproduction In Humans

• In males→ The male hormone is testosterone which is secreted by the

testis. It helps in sperm production & in the development of secondary
sexual characters.
The secondary sexual characters which develop in males after puberty:
 Growth of the testes & penis
 Growth of body hair (pubis, armpits, chest)
 Growth of facial hair
 Deepening of voice
 General overall growth spurt.

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• In females→ The main female hormone is oestrogen which is produced

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by the ovaries. It helps in the growth of the ovum and leads to the

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development of female secondary sexual characters after puberty.

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The female secondary sexual characters which develop after puberty:
 Development & growth of breasts.
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 Widening of the hip
 Growth of body hair
 Growth of uterus & vagina.
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Reproduction In Humans

Menstrual Cycle
• The menstrual cycle is the recurring or repetitive changes which take
place in the ovary & uterus of the female.
• This starts at the onset of puberty and is controlled by hormones.
• Every cycle lasts for 28 days.
• In the cycle: →The ovaries release one ovum alternately each month
into the oviduct.
→ The walls of the uterus increase in thickness in
anticipation of receiving the fertilized zygote. They become spongy &

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are full of small blood vessels for supplying nutrients and oxygen to the
developing embryo in case of its arrival.

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→ If fertilization does not take place, the thickened lining

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of the uterus gradually breaks down and the cells along with blood
pass out through the vagina. This is known as menstruation or
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menstrual period.
→ Menstruation lasts for around 5-7 days & indicates the
start of the next cycle.
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Reproduction In Humans

The start of the first menstrual period is an important indicator of the onset of
puberty in females.

Mechanism of Menstrual Cycle

The menstrual cycle is controlled by the brain & ovary by the interaction of
four hormones:

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Secreted by Pituitary Gland-

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• Follicle Stimulating Hormone or FSH
A small gland at the base of the
• Luteinising Hormone or LH

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brain.

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• Oestrogen Secreted by the Ovaries
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• Progesterone

⇒ A fresh cycle starts after menstruation.

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⇒ FSH is secreted by the pituitary gland: The group of cells surrounding

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the egg & the egg itself together known as the follicle starts developing
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due to its effect. Thus, FSH causes growth of follicle & maturation of
egg
⇒ The growing follicle secrets oestrogen which causes the thickening of
the lining of the uterus walls along with development of extensive
blood vessels. All these changes occur so that implantation of the
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zygote can happen smoothly if fertilization does take place.

⇒ On maturity of the egg: LH is released from the pituitary which is
responsible for the release of the ovum from the ovary into the oviduct
(Ovulation). Thus, LH causes ovulation.
⇒ After ovulation: the follicle transforms into a solid yellow structure
known as corpus luteum which secretes the hormone: progesterone.
⇒ Progesterone, like oestrogen has a similar effect on the uterus-It
promotes & helps to maintain the growth of the lining of the uterine
walls along with the blood vessels. It also inhibits the further secretion
of FSH & LH.
Reproduction In Humans

⇒ 2 scenarios can happen:

1. Egg undergoes fertilization→ Corpus luteum

continues to secrete progesterone & the
uterine lining is maintained. High levels of
progesterone also cause the stoppage of
menstruation & the subsequent menstrual
cycle. After implantation & the development of
placenta, the corpus luteum degenerates (after

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about 12 weeks) & placenta takes over the role

Mi y
of progesterone production.

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2. Egg does not fertilize→ The corpus luteum

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starts regressing (becoming smaller) and
progesterone secretion decreases & stops.
ah led
The thick lining of the uterus loses its support &
starts the process of break down. Menstruation
starts and the cycle is repeated.
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Reproduction In Humans

Sexually Transmitted Diseases

These are diseases in which the pathogen (virus or bacteria) can be passed
from one person to another by sexual contact. They are transmitted through
body fluids. Eg. HIV, syphilis etc.
Human Immunodeficiency Virus or HIV
• HIV is a typical virus with the genetic material (RNA) surrounded by a
protein coat with an additional lipid envelope.

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ah led
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• It causes the disease known as AIDS (Acquired Immune Deficiency

Syndrome) in humans.
• The persons infected with HIV are known as HIV positive. They do not
develop AIDS immediately & it may take several years (8-10 years)
before symptoms of the disease become evident. Thus, they can pass
the infection to other persons in the asymptomatic stage.
• HIV virus affects the lymphocyte cells of the immune system: mainly
the “T” lymphocytes. The level of T lymphocytes in the body decreases
drastically when the person develops AIDS. The body is then unable to
defend itself against other infections due to the weakened immune
system. Other diseases like pneumonia, cancer, tuberculosis start to
occur & may eventually cause death.
 Reproduction In Humans

Transmission of HIV infection

• Sexual contact: HIV is found in the semen, fluids of vagina & rectum
in the infected persons & may be transmitted by either of the
partners in case of unprotected sexual contact.
• Blood contact: HIV infection may be transmitted by direct contact of
blood of the infected persons
→ Drug abusers who may share needles & syringes.
→ In patients of haemophilia (a blood clotting disorder
where the patients have to be transfused blood

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clotting factors at regular intervals) & thalassemia (a
type of blood disorder where there is decreased

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hameoglobin production in the body. The patients

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require periodic blood transfusion for maintaining
their hameoglobin levels). These patients can get
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infection if they receive the blood or the clotting
factors from an infected person.
→ In persons who require a blood transfusion.
• Maternal Transmission: The baby of an infected mother can get the
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infection in the womb itself through placental transmission or

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during birth when the blood of the baby & mother can intermingle.
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HIV can also be transmitted to the baby through breast milk.

HIV is not transmitted by saliva, sweat, urine or faeces. So, one can easily touch or
share food & drinks with someone with HIV infection. It is also not transmitted by
the bite of insects like mosquito.
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Prevention of HIV Infection

1. Protected Sex- The use of condoms can prevent the transmission of HIV
through sexual contact as they can act as a physical barrier & prevent
the virus from infecting the other individual.
2. Free needle exchange schemes for persons who have to regularly inject
drugs so that re-use & shared use of needles & syringes is minimized.
3. Proper screening of donated blood for HIV antibodies so that infected
blood if found is not used for transfusion.
4. Education programs & awareness campaigns regarding the
transmission & prevention of HIV so that the general population can
get proper & reliable information about the disease.
Reproduction In Humans

Treatment of HIV infection

• Currently, there is no cure or vaccine for HIV infection.
• The virus is kept under check by a group of medicines which have to
be taken known as: Antiretroviral drugs or ART (anti-retroviral
therapy) which prevent the replication of the virus. They also
reduce the transmission of the virus & prevent the development of
AIDS. The patients can live normal lives but they have to take the
drugs lifelong.
• The antibiotics which are routinely prescribed for bacterial

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infections (eg. Penicillin) do not affect the HIV virus.
A virus like HIV does not have a cell wall or cellular enzymes & cell

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components on which the antibiotics can act upon.

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There is a difference between AIDS & HIV-
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• HIV is the virus which can infect an individual & the infected person is known
as HIV positive.
• AIDS is the name given to a variety of diseases like infections, cancer etc.
which can affect the HIV positive individual in the long term due to the
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weakened immune system. It usually takes years (8-10 or may be more) to

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develop.
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• It is not certain whether the HIV positive individual will develop AIDS in
future or not especially if he has started taking the medications.
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