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Class: 10

BIOLOGY NOTES
HOW DO ORGANISMS REPRODUCE?
…………………………………………………………………………………………………………………
Reproduction: Reproduction is the process of formation of new young individuals by the grown
up individuals that look very much like them
...

Thus, reproduction is meant for the continuation of the species
...
It gives rise to new
organisms with the same basic characteristics as their parents
...

Significance of Reproduction:1
...
Reproduction is essential for continuation of life on earth
...

2
...
Reproduction carries the genetic characteristics of the
parents into the new individuals
...

3
...
It is a means of replacing individuals killed due to ageing, disease or
predation
...
Population Characteristics
...

5
...
It introduces new variations
...
Transfer of Variations
...
There variations help the individuals in the struggle for existence
and adaptability to changed environmental conditions
...
(ii) Growth and differentiation of cellular machinery
...
It is mode of reproduction in single celled organisms
...

and
maturation
of
multicellular
organisms
...
They develop due
to (i) Faulty DNA replication (ii) Crossing over (iii) Chance separation of chromosomes
during meiosis and chance combination during fertilization
...
There importance can be put
as below:
a) Pre-adaptation:- Variation function as pre-adaptations to environmental changes like
increase or decrease in temperature, drought, antibiotic resistance, pesticide resistances
...
Reproduction normally maintains the body design, features
and functions suitable to that particular niche
...
They result in change of niches
...
However, variations present in some individuals n the
population may enable those individuals to survive, multiply and later form the
population equal to previous one
...
Variations provide individuality to each living organism
...

c) Struggle for Existence
...

d) Improvement of Varieties
...

e) Evolution
...

A) Asexual reproduction: The development of new individual with out the fusion of male and female gamete is
known as asexual reproduction
...
In asexual reproduction,
new individuals are identical to the parents
...

It can occur in the following ways
...
During this process the nucleus of the parent cell divides
mitotically into two equal parts which is followed by the division of the cytoplasm
resulting in the formation of the two identical cells referred to as daughter cells
...
e
...
amoeba
...


ii) Multiple fission: - In this process an organism is covered externally by a wall called
cyst, which protects it from unfavorable conditions
...
When favorable condition arrive, the
cyst is broken down and a large number of small organisms come out which are capable
of living at their own
...
g
...
It is also
known as Schizogamy or sporogamy
...
The
developingindividual its food from the parent and when it becomes fully mature, it
gets detached from the body of the parent to live an independent life
...
g
...


iv) Fragmentation: - In this process of asexual reproduction an individual breaks up
into several parts called fragments
...

Natural fragmentation occurs in algae
...
It may also
be induced by internal forces e
...
hydra
...
It takes place in opalina and
Pelomyxa
...
On return of the favorable conditions, the thick walls breaks open and a
germinating spore comes out which grows and reproduces in the usual fashion e
...

spores of bacteria like clostridium and bacillus etc
...


a) Vegetative propagation by roots: - In some plants like sweet potato, dahlia,
adventitious roots become thick and sworn due to the shortage of food
...
When such roots
bearing adventitious buds are planted in the soil they produce new plants
...
g
...
Similarly, in
some plants, under ground stems become modified as store houses of food materials

and gives rise to aerial shoots which get developed into new plants
...
g
...


c) Vegetative propagation by leaves: - In some plants like bryophyllum, the fleshy
bear adventitious buds their notches located on the margins when these leaves fall on a
moist soil favored by favorable condition of temperature and humidity, these buds
develop into small plants
...

Other methods of vegetative propagation
1
...
In this method
a piece of stem having few nodes and internodes is taken from the parent plant and
planted in the moist soil
...
The plants of
rose, sugarcane, banana, orange, and
bougainvillea are commonly grown by this method
...
Layering: - Layering means development of roots on a stem, which is attached to the
parent plant
...
Layering is a natural process, but can be induced by bending a plant
branch and covering its middle portion below the soil
...
After some time the portion of the branch below the
soil develops adventitious roots and can be transferred into an individual plant if planted
in a moist soil under favorable conditions
...
Grafting: - In this process of vegetative propagation, a detached twig having several
buds is planted or inserted into the stem or root of another plant to grow an individual
plant of the same kind
...
In order to avoid infection,
the point of grafting is covered with grafting wax
...
Tissue culture: - It is a modern method of vegetative propagation in which a small
tissue is taken from a plant and is allowed to grow in a medium containing all the
essential nutrients required for the proper growth of the plant
...
The callus is then chemically induced to form platelets, which are
transferred into pots or soil and raised to maturity
...
It is a cheap and easy method of reproducing the plants
...
The plants that do not produce viable seeds are easily propagated by this method
...
It is the only method of producing and preserving two plant types during crosspollination
...
This method is used to produce a large number of selected strains of plants without
loosing any desirable character
...


viii) Regeneration:- It is the ability to form missing parts
...
Each piece grows the missing parts and forms the complete organism
...
The ability to regenerate in differentiated
organisms is due to presence of special reserve or stem cells
...
Cells then undergo differentiation giving rise
to various cell types and tissues
...

B) Sexual reproduction: - In this process, development of new individuals takes place
by the fusion of sex cells of male and female gametes either from different individuals or
from different organs of the same individual
...
During sexual reproduction a gamete from male fuses with the gamete from
female
...
The
zygote develops into a new organism
...


i) Sexual reproduction in plants: - A flower is the reproductive part of plant
...
Sepals, petals, stamen and carpel
...
A flower bears a certain number of stamens
collectively known as androecium
...
The anther bear four chambers of pollen sacs, each filled with
pollen grains
...
A flower also bears one or more carpels
collectively known as Gynaccium or pistil
...


On the maturation of the flower, the stigma becomes receptive to the pollen
grains
...
Then the sperm fuses with an egg and zygote is formed by their fusion
...
After fertilization the
ovule develop into seed and the whole ovary becomes a fruit
...

Pollination: - The process of transfer of the pollen grain from the anther of a stamen to
the ovary of the carpel of the flower is referred to as pollination
...
It is of two
main types viz
...

Self-pollination:( Auto gamy) - This process involves the transfer of pollen from
the anther of a stamen to the ovary of the carpel of the same flower
...

2
...
It is a characteristic property of unisexual flower
...

The former include living beings such as insects and birds, while the latter include wind
and water
...
Insects –pollinated plants have flowers that are brightly coloured and
produce necter to attract insects
...
These are easily carried by the wind
over long distances
...
In some unicellular organisms the fusion of morphologically
identical gametes takes place, e
...
monocysts
...
The
union of such micro and macrogametes is referred to as anisogamy or herogamy e
...

higher animals and plants as referred to, in these animals the fusion of male and female
gametes occur and the process being referred to as fertilization
...
it generally occurs outside the body of the female (external
fertilization)
...
In some animals and man
it occurs within the body of the female (internal fertilization)
...

Fundamentally, the process of fertilization results into the restoration of the
diploid number of chromosomes determination of the sex of the new organism and
activation of the zygote to start a series of mitotic divisions called as cleavage
...

Fertilization: - Fertilization is the process, which results in the fusion of the sperm with
an ovum to form a single diploid cell called zygote
...

External fertilization: - It is a characteristic property of primitive organisms and
is an adaptation of aquatic animals
...


2
...
The reproductive organs become functional only after
attaining sexual maturity, which is attained at the age of 13 –14 years in males
...


1
...
Apparently human
sperms cannot develop at a higher temperature found within the body cavity
...

Each testis is composed of 200 – 300 coiled seminiferous tubules lined with epithelial
cells that produce sperms
...
It promotes development of
accessory glands and controls secondary male sex character along with the formation of
spermatozoa
...
Epididymis:- Epididymis is made up of a compact mass of small-coiled tubules
forming a convoluted tubule of 6 cm in length
...
Testes and Epididymis together constitute testicle
...

Filters them and makes them motile by the time they reach to its posterior part
connected with the Vasdeferens
...

Vasdeferens: -It is the muscular tube about 40 cms long that leaves the scrotum
by the inguinal canal and emerges with a duct from the bladder into the urethra
...
A glandular seminal vesicle empties into each
ejaculatory duct before it connects the urethra
...
The mixture of this fluid and sperm is known as semen
...

4
...
These discharge its secretion
directly into the urethra, which as alkaline in nature and contributes 15 – 30% of the
total volume of the semen
...

Cowper’s Gland: - These paired glands are also attached to the urethra about
5cm below the prostrate gland
...

6
...
It is composed of three columns of
spongytissues
...
Seminal Vesicles:- It can be seen at the base of the urinary bladder
...
Each seminal vesicle empties its contents into
the ejaculatory duct, adding to the volume of the semen
...


1
...
Ovaries
produce female gamete ova and the female sex hormones such as Oestrogen and

progesterone
...
The ovary releases one
ovum every 28 days
...
Oviduct (Fallopian tube): -Close to each ovary is an expanded funnel shaped
oviduct
...
Its walls are lined with
cilia, which sweeps the ovum towards the uterus
...

It curves outwards towards the sides of the abdomen
...
An ovum is produced and released alternatively from the two ovaries after every
four weeks and it makes take three days travelling down the oviduct to the uterus
...
If
the ovum is not fertilized, it is discharged during the next menstrual flow
...
It is connected to its
either sides to the fallopian tubes
...
The body of the uterus has
three coverings, the inner most endomatrium, the middle myomatrium and the
outermost perimatrium
...
The middle layer or myomatrium is muscular having several layers of
smooth muscle fibres
...
The cervix acts as a splinter muscle the close the uterine lumen
and prevents the foreign particles from entering into the uterus
...
Vagina: - It is large muscular tube of 7-10 cms long that runs from the uterus to the
out side
...
It also serves as a birth
canal during the birth of the child
...
It will never be implanted in the uterus in the unfertilized state
...
This is a sign of undoing the preparations it had made to receive the
fertilized egg
...
This process is called menstruation
...
Menstruation lasts for 3-4 days
...
To sum up,
menstruation takes place 14 days after the ovulation
...
In this way, ovulation and menstruation alternate
...
when the girls attain the age of 13-15, she
begins to ovulate
...
The menstruation stops in a woman in the late forties
and the ending of menstruation is called Menopause
...
It
requires the use of methods which prevent the fertilization of ova
...
Prevention of conceptions
called contraception
...

Contraception Methods:These methods involve prevention of fertilization and conception result in birth control
and is the basis of family planning
...

a) Natural Methods of contraception:- If copulation is avoided for a few days, i
...

at 3 days of the first day of ovulation which likely to be the time period when the ovum
is available in the uterus, fertilization can be avoided
...

Another natural method of contraception is coitus interrupts
...

b) Mechanical methods of contraception:- In this approach, various mechanical method
are used to prevent the passage of semen to the fallopian tube or to prevent
implantation
...

Diaphragm or cervical cap
...

c) Chemical methods of contraception
Spermicides
...

Oral contraception or pills
...
These pills
should be taken daily
...

d) Surgical methods
the ligature (tying by thread) of the vas deferens by a
surgeon is called vasectomy
...

In women, ligature of the fallopian tube can be done (tubectomy) to prevent
passage of ova down the fallopian tube
...
Diseases spread through sexual contact are called
sexually transmitted
diseases (STD)
...
syndrome(AIDS)

2
...
Gonorroea

4
...
Genital warts

6
...
It is sexually transmitted diseases it can pass from one
person to another during sexual intercourse
...

AIDS is a pandemic disease, I
...
it is found world over
...
It is
cell-mediated disorder of the immune system
...
Once the virus enters
the body it and grows in the body fluid and blood cell of the infected person
...

i)

Sexual contact with the affected person through semen or vaginal fluid or through blood
in case there is any tearing of tissues during the intercourse
...


iii)

Organ transplant from an affected person to a healthy person
...

Incubation period:- The average incubation period of HIV virus is about 28 months
(range 15-57
months)
...


ii)

Persistent dry cough, oral rash and shortness of breath may be observed
...


iv)

Gastro-intestinal problems like mild diarrohea may occur
...


vi)

A type of lung disease known as pneumocystic carnie pneumonia develops
...


vii)

Cancer or tumor of blood vessels known as Kaposi’s sarcoma may be seen
...

A completely infected AIDS patient may die within three years of infection
...

i)

Responsible sexual behaviour

•

Avoiding multiple sex partners

•

Using a condom or other barrier method of contraception which prevents direct contact
between body fluids of two persons
...


iv)

Avoiding pregnancy if the mother is HIV positive

v)

Education people
• Having knowledge of the ways by which AIDS can be spread and the precautions that
should be taken to avoid HIV infection
...

Models of spread: Sexual contact with the infected person can cause the disease
...

Incubation period: Symptoms of the disease occur in about 10-90 days after
contraction, but generally notice in 3-4 weeks
...
These can appear anywhere from 1090 days after contraction
...

i)

Fever and sores appear on the skin, in the throat and urinogenital areas especially vagina
or penis, anus, rectum and mouth
...


ii)

Break out of rashes on hands, feet and palms in seen
...


iv)

Acne-like warts are found in the groin area
...

Prevention and cure:•

Having sexual intimacy with only one person

•

Avoiding prostitution and homosexuality

•

Taking appropriate medical treatment
...
A large number of
gonorrhoea cases are reported each year
...
These symptoms are more common in females and
are usually more pronounced than in males
...

Modes of spread: As with most sexually transmitted diseases, having multiple sex
partners increases your risk of contracting it
...
Any kind of contact of sores with an infected person is also risk
...

Symptoms:
•

Inflammation of mucous membrane in the urinogenital tract
...

Differentiate Between
Binary Fission

Multiple Fission

1
...
It
individuals
...


Condition
...
Multiple fission occurs under
favourable and unfavourable
conditions
...


Nucleus
...


3
...


4
...
Cytoplasm undergoes
cleavage after each nuclear division
...
Cytoplasm does not divide
after every nuclear division
...


Residue
...
Example: Amoeba,
Paramecium

5
...
Examples:- Amoeba
Plasmodium(encysted

Unicellular Organisms

rise

to

two

1
...


Multicellular Organisms

1
...
The same cell
which functions as the body of
the organism also gets transformed
into reproductive cell
...


2
...
Technique of reproduction
are simple
...


3
...
It generally
occours through fission

It occurs by several methods like
fragmentation, regeneration,
budding, spore formation,
vegetative reproduction, etc
...


Sex Organs
...


They are present
...


Sexual Reproduction
...


through is ogamy to heterogamy

External Fertilization

Internal Fertilization

1
...
Fertilization occurs outside
the body of the female
...


2
...
Both the
sexes
discharge their gametes outside
their body
...
Surety
...


Only the male discharges the gametes and
also in the reproduction tract of the
female
...


4
...


Embryo is generally well protected
but may develop outside or inside the
body of the female

It is sure method of fertilization
...


Parents
...
e
...


Sexual reproduction is generally
biparental, i
...
,
involves to parents of different
sexes
...


Gametes
...


Gametes are always formed
...


Divisions
...


Meiosis occur once
...


4
...
Fertilization is absent
...


5
...
It is rapid method of

It is comparatively slower method

multiplication
...


6
...
They are genetically
similar to the parents
...


Variations
...


New individuals are genetically
different from either of the two
parents
Abundant variations occur during

All

the

division

s

are

sexual reproduction
...


Evolution
...


By producing variations, sexual
reproduction plays an important
role in evolution
...
Hydra and earthworm are such organism
...
Female gametes are larger in size than the male gametes but are non- motile
...

Puberty:- In humans , reproductive organs become functional only after attaining
sexual maturity
...
The age of attaining sexual maturity is called puberty
...

Placenta:- From the outer most membrane of the embryo, a number of out pushings
arise and get inserted into the inner wall of uterus of mother to form placenta
...

Umbilical cord:- It serves a link between the foetal and maternal circulation
...
This system of opposing effects leads to a proper control
and balance in the working of the organs
...
This is a kind of feedback information, which serves to bring
about a steady state or a stable state
...

Semen: -It is a thick viscous fluid, which is ejaculated at the time of insemination
...
In man the amount of semen discharged per ejaculation varies from 2
...
5 ml containing 200 – 600 millions of sperms and only one is needed for
fertilization
...
The head contains the haploid nucleus
...
The
middle piece has compact mitochondria
...




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