Friday 23 October 2015

note book work for reproduction in animals

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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