The 3 methods of asexual reproduction as
1. Fission
2. Budding
3. Regeneration
Fission :-
As the name suggests
in this method the body of the parent splits into parts, and
each part grows up as an individual.
If the body splits into 2, the method is called Binary
Fission as in Amoeba
If it splits up into more than 2 parts, it is called as
Multiple fission as in Amoeba,
Paramoecium, Leishmania ( causes Black fever or kala azar )
If the body of the parent splits into more than 2 parts it
is called multiple fission
as in the case of Plasmodium, the malaria causing bacteria.
During multiple fission, during unfavourable conditions, the
organism develops a
protective wall around itself inside which the cell matter
remains protected. This is
the cyst. The nucleus undergoes fission to form daughter
nuclei. Each one collects
a little cytoplasm around.
During favourable conditions, when the cyst breaks open,
these nuclei with their
cytoplasm are thrown out and each one lives life as an
interdependent organism
Budding :-
It is a process in which an outgrowth Is produced from the
body of the parent .
This outgrowth grows a little and then falls out and grows
into a new organism eg.
Hydra, Yeast
Regeneration :-
Definition :-
It is the process by which a new complete organism develops
from any cut part of
the body of a parent organism.
This is possible in the case of simple organisms where the
body is not developed into
specialized organs and tissues.
Eg. Hydra, Flat worm or planaria.
Sexual Reproduction in animals :-
This requires the
presence of 2 separate sexes with their own reproductive cells.
The terms used for male and female gametes in animals as
sperms and ova
respectively
‘Fertilization’ as an equivalent to pollination
There are 2 types of fertilization
iii. External
iv. Internal
Definition :- The union of a male gamete with the female
ovum during sexual fertilization to form
a zygote is called fertilization
The single fused cell which is the zygote multiplies and
forms a multicellular new
organism.
Human Sperm :-
Is an extremely small cell. It has a big head and a long
tail. The head contains the
nucleus which fuses with that of the egg.
The sperm also has a long tail which helps in the movement
of the sperm to the
egg and guides it to it.
The egg is slightly larger than the sperm. It contains
cytoplasm, nucleus, food and
water.
Gametes in humans contain half the no. of chromosomes as
that of a general cell.
Fertilisation :- This union of a sperm and the ovum may take
place outside the body of the
organism --- External Fertilisation or inside the body of
the female ---- Internal
Fertilisation
External fertilization takes place in the case of animals
like the frog or the fish,
where the female animal lays the eggs in water and then the
male spreads the
spermatic fluid over it.
Internal fertilization takes place in mammals, birds and
reptiles. In this method
the male gametes or the sperms are released in the body of
the female during
copulation process.
The fertilized egg called the zygote over a period of time
develops into an embryo
that grows into a young one inside the body of the mother
who then gives birth to it
as in the case of cats, dogs, humans.
In birds, the fertilized egg comes out in the form of the
egg as in the birds. This grows
into an embryo outside the body of the mother who gives it
warmth by sitting on it
( hatching ) and the young baby breaks open the shell and
comes out as a young
Nature has to prepare the body for the process of
reproduction and this period
or phenomenon is called Puberty
Definition :- The age at which the sex hormones and gametes
begin to be produced
by the individual who then becomes sexually mature is called
Puberty.
The onset of puberty is the stage of Adolescence ranging
from 10 to 12 in girls
and 13 to 15 in boys.
Sex hormones are produced in this period which gives the
distinct
characteristics to the external structures and physiological
traits to the two
sexes.
The changes that occur in girls are ---
i. Growth of hair in the arm pits and the pubic region
ii. Enlarging and development of mammary glands
iii. Broadening of hips
iv. Enlarging of the fallopian tubes, uterus, vagina
v. Start of the Menstrual cycle.
vi. Feeling of sexual drive.
The changes that occur in the boys are ---
i. Hair in the arm pits and the pubic ( genital ) area and
chest
ii. Facial hair in the form of moustache, and beard
iii. Penis and testes become larger
iv. Cracking of voice
v. Development of muscles and broadening of shoulders
vi. Feeling of sexual drive ( produced by the hormones )
The start of the menstrual cycles is called Menarche ( 10-12
yrs )
The end of menstrual cycles is called Menopause ( 45-50 yrs.
)
Definition :- The permanent stoppage of the menstrual cycle
is called Menopause
Male reproductive system:-
Gametes : Sperms . They are produced in large nos.
Location : Produced in the testes. Testes also produce the
male sex hormone
called Testosterone ( responsible for the male
characteristics )
scrotum. The
temperature outside the abdominal cavity is lower than the temp.
inside and hence it is a suitable environment for the
production and survival .
Testes are held
outside the abdominal cavity in a sac called the
Journey of the sperms
:- There is a layer on the outside of the testes called the Epididymis which
has a sac –like structure on the upper part of the testes to hold the sperms
for a short period of
From the epididymis they
enter a tube called the Vas Deference
and travel down
it. Along their journey the mix with the secretions of the Seminal Vesicles and the
Prostrate Glands.
These secretions provide nutrition to the sperms and also form a
fluid with them and help the sperms to travel smoothly.
The thick liquid formed by the secretions of the Seminal
Vesicles and the Prostrate
glands along with the sperms is called the Semen.
The Vas Deference meets a tube from the urinary bladder . It
is the Urethra which
carries the sperms to an organ called the Penis. It is the
common passage for the
urine and the semen.
The sperms are deposited in the vagina of the female during
mating.
Female Reproductive System
it is more complex than the male reproductive system as it
is the meeting place of
the 2 reproductive cells and also the growth of the embryo
into an individual and
the its birth.
Gametes : Ova or eggs.
Location : In the ovaries. They are the two primary
reproductive organs placed
inside the abdominal cavity near the kidneys. They produce
the ova and the
female sex hormones called the Oestrogen and Progesterone.
The unripe ova are called the follicles. They mature and are
ready for fertilisation at
puberty.
Journey of the ovum :
The ova are produced by the ovary.
These ova enter the funnel of the Fallopian Tube or the
Oviduct which cover the
ovaries . All the eggs grow, but only one grows maximum and
it is the one that will
get fertilized by the sperm
The sperm meets the ovum in the oviduct and fertilisation
takes place here.
The fertilized egg travels along the oviduct.
The 2 oviducts open into a pouch-like organ called the
Uterus.
The growth of the fertilized egg into a foetus takes place
in the uterus.
At the time of birth the baby is sent out of the body of the
mother through the
vagina or the birth canal
Menstruation :- The Ova receive the sperm and fertilisation
takes place.
Simultaneously the uterus prepares itself to receive the
feritilised egg. It develops a
thick lining on its inner walls and the blood supply to this
region increases.
In case the fertilisation does not take place, the uterus
sheds this thick wall along
with blood, which comes out through the vagina.
This is Menstruation. This cycle takes place every 28 days
as the uterus keeps on
prepares itself to receive the fertilized egg.
Fertilisation :- Definition :- The union of the male and
female gametes to form the Zygote is called Fertilisation.
In humans the sperms which are deposited in hundreds in the
vagina of the female
travel upwards with the help of their long tails through the
uterus into the oviducts
where there is only one egg ready for fertilisation.
One sperm out of these unites with one egg. Their nuclei
unite and the haploid
nucleus becomes diploid
This is why the reproductive cells have half the no. of
chromosomes as that of a
normal cell, so that the fertilized cell ultimately has the
full set of chromosomes half
the set coming from each parent.
The zygote travels to the uterus and lodges into a pit in
the thick wall of the uterus .
This is called implantation.
After the embryo has implanted itself a special tissue
called PLacenta is formed
between the foetus and the uterine wall
The foetus ( unborn baby )receives nutrition from the mother
through the umbilical cord. The period during which the embryo grows into a
fully grown baby is called
Gestation which is 280 days
At the time of birth the uterus starts contracting and
pushes the baby out along the Vagina or the birth canal.
When the baby is born, the uterine wall along with the
placenta also comes out.
Cutting of the umbilical cord cuts off the physiological
attachment of the infant
with the mother.
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