Cnapte

8 Reproduction
What I Kne.

reproduce.
studied how plants or
In the previous class, youdifferent reproductive parts
recognise the
Hecall and
a flower

REPRODUCTION
ones that resemble the living
living organism is able to produce
young
which a
The process by turns into a plant when
it grows, likewise,
organism is called reproduction| Just like a seedling
to maintain their number and also for
into a dog. Efving organisms reproduce
small pup grows
different ways. For example, animals
the continuation of their species. All species reproduce in
such as dogs and cats give birth to young ones, whereas birds lay eggs in nest_. The animals tha
give birth to their young ones and feed them with mother's milk are called mammals.

METHODS OF REPRODUCTION
There are two methods of reproduction-sexual and asexual.

Asexual Reproduction In this method of reproduction, a single parent giyes rise to

new individualIt
does ot involve the fusion of male and female gametes.The the
produced by thia method are the exact replicas of their oftsprng
some organisms that reproduce by asexual reproduction.parent. Amoeba, Hydra and yea
Sexual ReproductionJn this method of -
parents are involved Both
the
reproduction,
both the male and the
femaic
gametes fuse to form a parents have
reproductive
organs Male and femaie dog
and cats are some zygotehis
that Zygote develops into a new
organisms individual)Huma
reproduce by sexual reproduction. ans,

110
EXUAL PRODUCTION
Nual reprodüctrón involves the fusion of both male and female gametes. Both the parents
reproductive
have reproduci organs that produce cells (or reproductive cells). Most animals and
sex
nlants reproduce by sexual reproduction, The male reproductive organ produces sperm and
plants reprodu

the female reprgductive organ produces ova (singular: ovum.. The sperm and ovum fuse
to form zygotehs zygote isa single-celled organism. The process of fusion of sperm and
o4m is called fertilisation, the zygote undergoes cell division several times to develop into
an embryoT his embryo then develops into a new individual.

Pgg cell (or ovum) +Sperm cell Zygote

In some organisms such as humans cows and dogs, the male and female gametes are present
in two different individuals. While in some organisms, like earthworm, both the male
and female gametes are contained within the same individual. These organisms are called
hermaphrodites.

Fertilisation in animals can take place by two ways-internal and external.

nternal fertilisation: When the fertilisation takes place inside the body of a parent, it is
called internal fertilisation. The chances of survival of an offspring are more in internal
fertilisation.
Ex1ernal fertilisation: During rainy season, a female frog comes out of the pond to lay
millions of eggs. The eggs are fragile and do not have an outer covering or shell to protect
them, so they are held by a jelly-like substance. The male frog comes and releases its sperms
over the eggs. The sperms are motile and
randomly fertilise the eggs. Not all the eggs get
fertilised, some get washed due to wind or water. The eggs that get fertilised produce zygotes.
This kind of fertilisation is called external fertilisation. Most aquatic animals show external
fertilisation.

REPRODUCTION IN HUMMANS
Humans reproduce by sexual reproduction. It involves two sexes-male and female. The
fertilisation is internal, that is, inside the body of the female. Also, the complete development
of zygote happens inside the female body. Both the sexes have reproductive systems to help
in
reproduction. The reproductive systems are masire at the time of puberty. In boys,the
sexualmaturity occurs at 11 to 15 years.ot agelowever, in girls it occurs at 10 to 15 years
of ageThe stage of
life when the body becomes sexually mature or capable of reproduction
1S called puberty/The males and the females have different reproductive organs. Let us study
about each one of them.

111
 Female Reproductive System
The female reproductive s ystem consists of the follovwing parts.

Y
a. A pair of ovaries

. Oviduct (or fallopian tube)

c. Uterus Ovary

d. Cervix

e. Vagina Fig. 8.1 Femae rrs.

Ovaries occur in pairs and are placed on either side of the abdomen.
Ces
The ovaries produce ova (singular: ovum). These also secrete female
hormones estrogen and prPgesterone, which regulate and maintain
female reproductive cycle, During the menstrual cycle, one ovum
is released from either ofthe ovaries. The ovum is a single-celled
structure If the ovum gets fertilised by the sperm, zygote formation
occurs. However, if the ovum is not fertilised, it is released out of the Fig. 8.2 A ovr
body The fertilisation takes place inside the fallopian tube and development of embryo occn
inside the uterus (also called thee womb). Uterus has the capaciry to nurture the child.TTe
cervix serves asan opening to the uterus and the vagina is called the birth canal or the org
of copulation Copulation is the act in which a male reproductive organ enters the temaie
reproductive tr ct to discharge the male gametes.

Male Reproductive System Seminal vesicle Urrary DaE

The male reproductive system consists of Ejaculatory duct
Prostare Jsr
the following parts.
Vas
a. Testes
b. Urethra Epididymis
Testes
c . Vas deferens Penis
Epididymis Urethra
ens
e . Penis
Fig. 8.3 Male reproductive sysem
Testes are the male reproductive organs
that produce sperms, the sex hormone (testosterone), as well
as accessoryglands{Testes are presept outside the abdominal PesTe mentrar

cavity in a sac calBed the scrotal sac Testes produce millions

of sperms at a time. A sperm is single-celled and has a head,
middle piece and a tail. Unlike ovum, sperms are motile.
Epididymis helps in thé maturation and storage of some.
sperms. The sperms leave asperm duct
thetestes through
called vas deferensThis duct also collects fluids Fig. 8.4A human s p e
 ereted by
secreted by other glands. These fluids are rich in proteins and provide energy to the sperms
(Sperms along with these secretions form a thick substance called semen. The penis transports
the sperms into the vagina of the female. It serves as a common
sperms into and
the transporting organ for urine
cemen. It opens out through a small tube cailed urethra.

Fertilisation FactAce
During the act ot copulation, sperms are released into the The longest gestation period
is that of the elephants. It is
vagina of the female near the cervix. About 500 million
about 90 weeks.
sperms areproduced in a single ejaculation. The sperms
being highly motile Swim with the help of their tail inside the uterus and climb upwards to
the
fallopian tubeoniy rew sperms reach the fallopian tube, whereas the rest die or get absorbea
by the lining/It the ovum is present
inside the tallopian tube, then the
Fertilisation
sperms surround itfAs soon as one
sperm enters the ovum, the entry
Egg (Ovum)
of other sperms is prevented by
the fertilisation membrane/Inside
Zygote Embryo
the fallopian tube, the fertilisation
takes place and the single-celled
Sperm
zygote is tormed which transforms
into an embryo within a few weeks. Fig. 8.5 The process of fertilisation

In-vitro fertilisation
Fertilisation taking place outside the human body is called in-vitro fertilisation the babies
thus produced, are called test-tube babies(Fresh ova are collected from women who cannot
bear babies/These ova are maintained-under sterilisedeonditions and are fertilised with
the spercotectedfrom the husband of the woman)the zygote formed develops under
controlledconditionslThen, the embryo is transferred into the uterus of a surrogate
mother. The baby develops in the surrogate mother's womb and is delivered at the end of
nine mónths.)

Embryo Development
The zygote undergoes repeated cell divisions to form he embryo the embryo gets embedded
in the uterus wall, where further development
occursGradually, the embryo divides and
different cells are formed which then perform speciafised functions. This is çalled cell1
differentiation (or cell maturation)|The cells then torm tissues and organs. At about 6 to 8
weeks, the embryo reaches the stáge where it can be recognised. This recógnisable form is
called foetus The foetus develops completely in about 40 weeks, after which the childbirth
Occurs. This period is called the
of
gestation period and it varies from animal to animal. In case
human beings, it is of nine-months.

estation: the period during which an embryo develops

113
 CHRCKPOINT1
1. State whether the following statemente are True or False.
The human female gamete
a. Dogs are hermaphrodites.F C.
isthe
b. Sex cells are also known as the sperm.F

d. is the result of
reproductive cells. Zygote fertilisati,
e. Embryo is not formed by cell
ell satdivie
ion.T
division
2. Fill in the blenks.
a. The process of fertilisation can be AMMa... or ..eNEY.0QA
b. .00tus... is the stage when embryo becomes recognisable.
c. Fertilisation that takes
place outside the human body is called * A a l In
d. Sperms leave the testis through the duct called Nab..duMum
e. The ovaries secrete the female hormones 9aHon. and
poqlnma
vIVIPAROUS AND OVIPAROUS ANIMALS
Some animals, such aa dogs, cats, cows and tigers HOTS
which give birth to young ones are called viviparous
How are twins born? What are
animals) Some pnimals, such as birds, frogs and fish Siamese twins?
lay eggswhich later develop into young ones are called
oviparous animals. In oviparous animals, the complete
development takes place inside the egg and then the egg FactAce
hatches to release the newborn to the world. When the ovum does not gett
fertilised, it is released out of
Birds, such as the hen, lay eggs and then sit on them the uterus along with blood. This
to keep them warm. The type of fertilisaion in hens is process is called menstruation.
internalfertilisation.[n hens, the zygote isformed after
fertilisation that undergoes multiple repeated cell divisions and travels down the oviduct.
(During this travelling, many protective layers are formgd outside the zygote including the
Outer hard shell The embryo turns into a chick in about21 days, during which the hen will
sit on the egg and give
it warmth. This is called the end of 21 days, that is, tho
incubation At
incubation period, if the eggs are fertile, they will hatch.

a. Tiger and cubs b. Chickens

Fig. 8.6 Viviparous and oviparous animals
114
METAMORPHOSIS
In most
of the cases, the young one reproduced resembles its parent(s). But when it comes to a

hiutterfly or a trog, this is not the case. The young one of a frog, called the tadpole, resembies
a fish.
Similariy, the
young one of a butterfly, called the caterpillar, also does not look like an
adult buttertly. Let us study the life cycle of a butterfly and a frog

Four Stages: Egg Caterpillar Pupa- Butterfly

Metamorphosis Caterpillar

Chrysalis
or pupa

Egg

Butterfly

Fig. 8.7 Stages in the life cycle of a butterfly

2
ladpole

3
adpole
Eg99 po

5Adult
trog
Froqlet

Fig. 8.8 Stages inthelife cycle of a frog

115
 ACTIVITY1 water
er
s m a l l plants,
of a frog
To study the life cycole gless
container

e frog, ig
Materialsrequrod: eggs of
Procedure: AlSu, keep son
a t e r . Also,

. y and collect a few eggs of a r9hcOntains

container
thet
water.
w
conteins
smal pa
2. Place the eggs in a biggless ike crea
fish-like
smallfishHike creatures.
along with the eggs hatch intosmall
into a fish
ese
eggshatch
eggs
the the water
lke
and come t
3. Ater a few deys enthatthe
seennat swim in
talls. They
Iney start to e
oreetures are
el tadpoles. The tadpoles
are called tedpoles. ine odnoles
tadpoles
even have tails.
even have e
reatures
neS The
breethe.
to
the surface of the water
inside the container. and the
disappear and startto
tne legs start tn
appea
Pents thet are present tails ofthe tadpoles
.Ater 12 to 14 weeks the an aduicnog
starts resembling
s SEage, the tadpole
resemble the frog
Observations: The tedpole does not only, under teacher's g eacher's guidanc
the science laboratory
Note: The actvity must be done in

conclude that the

life cycle of a trog consics
ists ois
we can
rrom Activity 1 and Figure 8.8,
stages.
anda frog undergo majorchan
that the eggs of a butterfly
From these activities, we
see
a
of animalinto completelydifferen
a
become an adult. This conversijon oftheyoung that
occurs diterent stages, Suddena
to in en and
is a biological process looks completely different in aprea
Scalled metamorphasist
occurin the young one and the adult
abrupt changes

ASEXUAL REPRODUCTION
It does not require the fusion of
This method of reproduction involves only one parent.
this method are the exact replicas
and female parents(The offspring produced through Here we will be studying
theirparents There are different types of asexual reproduction.
about binary fission and budding.
2

Binary Fission Formatond

daughter AmEB
Lower organisms such as Amoeba
replicate by binaryfission The
singleçell divides into two halves.
SinceAmoeba does not have a Amoeba with
nucleus.
a
Nucleus divides
into two.
Each part receves
a nucleuS.
fixed shape, the division of the cell
can take placesither laterally
or
Fig.8.9 Binary fission in Amoeba
longitudinally,When the cell divides,
the nucleus ofthe cell also gets split equally, and similarly, the cytoplasm alsodivides
divides egual
daugha
The daughter cells grow completely before theysplit into two different entities.he
cells formed are replicas of the parent cell.

116
 Budding

Rudding is type of asexual

another

reproduction Organisms, such as Bud grows and

forms a

Hydra with a bulge known |

Hydra, exhibit
reproduction by as bud
baby Hydra

budding.Onthe body
of a lHydra,
small projections
or bulges can
seen. These appear
because
be
of repeated cell divisions.A new 3
formed from these
organism Is The bud is fully
hence the
butges (called buds), The fully mature baby Hydra
mature.

narme budding. These buds develop separates from the parent.

intonew individuals. When the

individual is completely formed, it
detaches itselt from the parent and Fig. 8.10 Budding in Hydra
begins individual.
to grow as a new
Budding is also shown by unicellular organisms such as yeast.

CHECKPOINT 2
Answer the following in one or two words.
1. Example of an oviparous animal. t d
2. Type of asexual reproduction exhibited by Amoeba.Eino-doung
Fig
3. The young one of a frog. Tad pols
4. Incubation period of a hen. 2l day
Animals that give birth to their young ones. NipaOU,

DETERMINATION OF GENDER OF A BABY

Have you ever wondered what determines the sex of a baby? How do we know whether
the child will be a male or a female? In a human body, thereare 23 pairs of chromosomes.
The 22 pairs of chromosomes are responsible for our physical characters that get inherited
from our parents. The 23rd pair of chromosome, also called the sex chromosome, is what
determines the sex of a baby. A female has 22 pairs+ XX chromosomes, whereas a male
has 22 pairs + XY chromosomes. So, when an egg is tertilised by a sperm that contained
Y chromosome, the zygote will develop into a male child; however, when the egg gets
fertilised by a sperm containing the X chromosome, the zygote will develop into a female
child.
From this, it can be concluded that it is the chromosome of the father that determines the sex
of the child and not the chromosome of the mother.

117
 (22 pairs XY chromosomes)
+
(22 pairs +XX
22 pairs + X
(R) Father 88Mother
hromosomes
22 pairs+Y 22 pairs + X 22 pairs+ X
Sperm formation
(R (8 (B) Ova formation
()
22 pairs + XX
22 pairs +XX 22 pairs+ XY 22 pairs + XY

Fig. 8.11 Method of

determining the
gender of baby a
Gender Issues and
In India, there
Myths
are a lot of
male dominates the gender-related issues. The society is mostly patriarchal,
society. The male is considered as the head where the
households. So, in rural of the family in most
Indian
areas, where
At some
places(the girl child is even people not well-educated, they prefer boys over girls
are

because she is considered a killed while she is still inside the womb of her
burden. This is called female mother
foeticide.)To stop this, the government made an
has
to ban fhe
practice of revealing the sex of initiative
the unborn child to
HOTS G
the expecting
parents. At almost all the hospitals and A mother has
given birth
clinics, it isillegal to disclose the the private to a female child. What
sex
baby. are the sex chromosomes
CLONING given by both the parents?

Cloning is the process of creating clones of an

is the exact
replica of the individual. already existing individua!The
Various clone produca
worldwide.(The first animal to be cloned wascloning experiments have been carried
asheep called Dolly. The cells out
collected from the udder of a
sheep. Before the actual embryo 6-year-old female for cloning wer
of Dolly, the
sheep, developed, almost S00
development failed. The birth attempts
of Dolly
of embryo
1. Can human
HOTS
announced much later after its actual sheep was cloning be referreo
continued to live only for 6 years. Sincebirth. She to as a natural
process when
Identical twins are delivered?
of cloning then, lots
experiments
various animals.
have been
conducted on
2. Do
you think there can be ethico
Sues regarding cloning? ye
what couldthey be?
118
Udder: Mammary alan
 KEY WORDS

duction: The process by which a living organism produces its young ones
production:

Aep ion: The process of fusion of sperm and ovum

Fertilisation

nal fertilisation: Fertilisation taking place inside the body of a female

rnal fertilisa

Intefertilisation: Fertilisation taking place outside the body

External ferti

uberty: The stage of lfe when the body becomes sexually mature or capable of reproducu

ro fertilisation: Fertilisation taking place outside the human body

In-vitro fertilis

Viviparous animals: Animals that give birth to young ones

Oviparous animals: Animals birds that lay eggs
or

Metamorphosis: Iranstormation of a young one into a completely different adult

claning: The process of creating clones of an already existing individual

SUMMARY
The process by which an animal (or any other living organism) is able to produce young
ones that resemble the animal (or the living organism) is called reproduction.
There are two methods of reproduction: sexual and asexual.
Sexual reproduction involves the fusion of both male and female parents.
In asexual reproduction, a single parent forms a new individual.
The fertilisation takes place inside the fallopian tube whereas, development of embryo
OCCur's inside the uterus.
Testes are the male reproductive organs that produce sperms.
The zygote undergoes repeated cell divisions to form the embryo.
Birds, such as hen, lay eggs and then sit on them to keep them warm. This type of
fertilisation in hens is internal fertilisation.
The young one of a frog, called the tadpole, resembles a fish and the young one of a
butterfly, called the caterpillar, also does not look like an adult butterfly. The eggs of such
organisms undergo several transformations to become an adult through a process called

metamorphosis.
Amoeba replicates by binary fission and Hydra reproduces by budding.
Ihe 23rd pair of chromosome, also called the sex chromosome, determines the sex of
a baby.