CHAPTER-3

HOW DO ORGANISM REPRODUCE

REPRODUCTION
Reproduction is the biological process by which an organism reproduces
new individuals of the same kind.
Advantages of Reproduction
 Reproduction ensures the continuity of a particular species on
earth.
 It creates genetic variation which leads to the stability of a species.
 It helps in the evolution of a species.
DNA(DIOXYRIBO NUCLIC ACID)
A group of molecules responsible for carrying and transmitting the
hereditary materials or the genetic instructions from parents to offspring.
GENES
The fundamental unit of heredity.
Importance of DNA coping
DNA contains information for the inheritance of characters from the
parent to the next generation as a result of DNA copying blueprints of
body designs are produced which passes from parents to the offspring
thus DNA copying maintains the body features in different generations
of a species sometimes DNA copying also creates variations which are
useful for the survival of species over time
 Importance of Variation
 Variation helps organisms to adapt to the changing environment.
 Variation provides stability to a species and thereby helps in
evolution.

Sexual reproduction Asexual reproduction

It requires the fusion of the male and It does not require the fusion of the male and
female gamete. the female gamete.

It involves two (usually) different

It involves only one individual.
individuals.

It involves germ cells of the body It involves somatic cells of the body

The offspring produced in sexual Offsprings produced in asexual reproduction

reproduction are different from their are exactly similar to their parent. Hence,
parents Hence, it shows variation. they are called clones.

They are evolutionarily advantageous. They are not evolutionary advantageous.

Meiosis and mitosis division both take

Only mitosis division takes place.
place.

It is a slow process. It is a fast process.

Found in only lower invertebrates and lower

Found in higher plants and animals.
chordates.
ASEXUAL REPRODUCTION
When offspring is produced by a single parent with or without the
involvement of gamete formation
TYPES OF ASEXUAL REPRODUCTION
 Fission
 Fragmentation
 Regeneration
 Budding
 Vegetative propagation
 Spore formation
FISSION
 Unicellular organisms such as Amoebas, Paramecium, Euglena,
and Plasmodium) reproduce through a mode of asexual
reproduction called fission.
 In this mode, the parent body divides into two or more daughter
cells, each growing into an adult organism.
 It is of two types binary and multiple fission
BINARY FISSION
 Binary fission involves the division of the parent into two small,
nearly equal-sized daughter individuals.
 During binary fission nuclear division occurs first, followed by the
division of cytoplasm into two parts producing two daughter
organisms.
 Binary fission occurs in unicellular protozoans like Amoeba,
Paramecium, Euglena, etc
 Eg- Amoeba-Irregular, Paramecium-transverse, Euglena, yeast,
leishmanial-longitudinal etc
 LEISHMANIA(binary fission)
 It causes kala-azar
 It is a unicellular organism
 It has a whip-like structure at one end of the cell
 It has a longitudinal division
MULTIPLE FISSION
 Multiple fission involves the division of parents into many small
daughter individuals.
 Nucleus divides several times many daughter nuclei, without the
division of cytoplasm. Example: Plasmodium
Plasmodium
When the conditions become unfavourable, a tough coat called a cyst is
formed around the cell. On return of favourable conditions, the cyst wall
is broken and many daughter cells are released.
FRAGMENTATION
Some organisms like Spirogyra upon maturation break into smaller
pieces. These pieces or fragments grow
into new individuals.
For Example: Hydra, Spirogyra
Spirogyra
Spirogyra breaks into many pieces and
each piece grows into a complete filament.
This process is known as fragmentation.

REGENERATION
A fully differentiated Organism can give rise to a new individual
Organism from its body part. The body part that contains a specialised
cell growth or regenerates into separate individuals
Eg-Hydra, Planarea, Starfish etc
Planaria
Small fragments or pieces of their
bodies can grow into complete
individuals.
BUDDING
This is the method a bud-like projection is formed on the body of the
Organism the bud then
develops into a new
individual. It then
separates from the
parent and forms an
independent individual.
Eg- hydra, yeast etc
SPORE FORMATION (RHIZOPUS)
● Different types of asexual reproduction spores
are produced in these organisms.
● In many fungi, at the time of spore formation, a
swollen structure known as sporangium develops at
the top of the fungal hypha.
● These spores are very small, light and variously
coloured in different fungi.
● The spores germinate to give rise to new fungus after falling on a suit
VEGETATIVE PROPAGATION
New Organisms can grow with the help of (leaves, roots & stems) but
not with seeds.
Two Types:
● Natural Vegetative Propagation
● Artificial Vegetative Propagation
Natural Vegetative Propagation
● Grown without any human help.
● New plants grow from leaves, roots & stems of the parent plant.
By Underground stem
Tubers:
● Swollen and fleshy
● Example - Potato
● Buds (eyes) are present in potatoes, which grow
into a new plant.
By Root
● Plants like sweet potato (Tuberous roots),
Dahlia,
Tulips have fleshy roots.
● Roots have buds which detach & give rise to
new
plants.
By Leaves
● Leaves like Bryophyllum & Kalanchoe
produce adventitious buds on the margin of
their leaves.
● The buds fall and develop into plantlets.
Artificial Vegetative Propagation
● Adopted by human beings.
● It is a Faster Method.
● It is used in gardens and nurseries.
Cutting Vegetative Propagation
● A propagule is cut from the parent plant & put into the soil, which will
form a new plant.
Stem Cutting:
Example: Rose, Bougainvillea, Chrysanthemum, Grapes, Sugarcane,
Banana, Cactus etc.
Root Cutting:
Example: Raspberry, Blackberry, Dahlia, Fig, Lilac
Layering
Mound Layering
● A branch with leaves is bent to the ground
& a part of the stem is buried in the soil.
● A cut is made in the parent plant, which
grows into a new plant.
Grafting
● The stem of one plant (scion) is cut and attached to the root of another
plant(Stock).
● After some time, the attached stem and root combine to form a single
plant.
● Cambium of both scion and stock should be in contact.
Advantages of Vegetative Propagation

● Quick and cheap method to produce a large number of plants.

● Disease-free plants can be produced.
● Desired characteristics of plants can be introduced.
● Genetically identical plants can be produced.
● Survival rate of new plants is almost 100%.

SEXUAL REPRODUCTION
 Involves two different sexes, Male & Female.
 Each parent produces special sex cells or germ cells (gametes)
 The fusion of male and female gametes forms Zygote.
 Zygote then divides repeatedly to form multicellular organisms (by
cell-differentiation).
Significance:
 Promotes diversity of characteristics.
 Creates a new combination of variations, which is necessary for
evolution.
Sexual reproduction in plant
CALYX
 It is the group of sepals
 It is the outermost wall consisting of sepals
 It helps in pollination
 sepals are green and leaf-like structures
 Calyx protects the flower bud before it opens
COROLLA
 It is the group of petals
 It is the second wall, inner to the calyx consisting of petals
 It helps in pollination petals are generally larger coloured and
showy
 Corolla attract insects for pollination
ANDROECIUM
 It is the third wall, inner to Corolla
 It is the male reproductive part
 It consists of the male reproductive part stamen
 Each statement has two parts filament and another
 Anther is a lobbed structure present at the tip of the filament anther
has a pollen sac that contains pollen grains
GYNOECIUM
 It is the fourth and innermost wall consisting of carpels
 Each carpel has 3 parts the ovary, style, stigma
 The ovary is the swollen basal part of the carpels
 Each ovule contains an embryo sac that bears a haploid egg
 Style is the middle part of the carpels
 It has a stigma above and an ovary below
 Stigma is the apical part of the carpel
 It receives pollen grains
Types of Flowers
Bisexual Flower
Both stamen and pistil are present in the same flower
Unisexual flower
Either stamen or pistil is present
Pollination
Transfer of pollen grains from the anther of the stamen to the stigma of
the carpel is called Pollination.
Some agents of pollination are Wind, Water, Animals, Insects, etc.

Agents of Pollination:

Abiotic- Wind and Water.

Biotic- Birds, Insects, Reptiles and Mammals
 Fertilisation in plant

Fertilisation
 One pollen tube grows into the stigma and passes
through style and then to the ovary.
 Two non-motile male gametes are formed.
 The tip of the pollen tube ruptures releasing two
male gametes into the embryo sac.
 The embryo sac consists of an egg apparatus (one
haploid egg cell and two synergids), two polar
nuclei & three antipodal cells.

Post Fertilization
 Development of Endosperm and Embryo.
 Maturation of ovules into seeds and ovary into fruits

Seed Germination
 Seed is the final product of Sexual Reproduction.
 Seed develops into embryo and embryo develops into seedling
under favourable conditions
 A seed consists of a SEED
COAT, cotyledon, and an
EMBRYO AXIS.

Human Reproduction
Germ Cells
 These are special cells that are involved in Reproduction.
 Produces gametes - Male cell/sperm produces male gamete -
female cell/egg produces female gamete
PUBERTY
Puberty is the period or stage of human development during which an
individual shows growth and becomes mature.

Female Reproductive System

❖ Ovary
 Ovaries are the primary sex organs of a female.
 Each ovary performs a dual function of 1) Production of female
gamete (ovum or egg) and 2) Secretion of female sex hormones
(estrogen and progesterone).
❖ Ovulation
 Release of ovum from the ovary
❖ Fallopian Tubes (oviducts)
 Channels the egg down to the uterus. Fertilisation happens here.
 It also provides the site for the fusion of ovum and sperm.
 They receive eggs, released from the ovary.
❖ Uterus
 Ensures and supports the creating child. The uterus is lined by
endometrium.
❖ Cervix
 Ring of muscles that is near the lower end of the uterus.
❖ Vagina
 Gathers sperm deposited by the penis, and acts as a birth channel
for a child

Male Reproductive System

❖ Testes
  Testes are primary male reproductive organs.
 They lie in a small sac-like muscular structure outside the
abdominal cavity called the scrotum.
 Testes form sperms throughout the reproductive life.
❖ Scrotum
 It contains the testicles
❖ Epididymis
 It receives sperm from the testes and stores them temporarily till
ejaculation.
❖ Seminal Vesicle, Prostate Gland
 Secretions of these glands protect sperms from the acidity of the
male urethra and female reproductive tracts. Secretions also
increase sperm motility.
 Secretions of these various glands and sperms collectively form
semen.
❖ Vas Deferens (sperm duct)
 Works in transporting sperm to the urethra
❖ Bladder
Stores urine

❖ Urethra
 Conveys sperm and urine to the penis where they are discharged.
❖ Penis
Deposits sperm inside the vagina; furthermore
disposes of urine
Fertilisation
  After copulation, millions of sperms are released during
ejaculation.
 Sperms swim towards the female egg, with the help of the tail.
 Only sperm will fertilise the egg.
 The fertilised egg will move towards the uterus.
 Zygote forms foetus and Foetus changes to embryo.
Implantation
 Attachment of growing embryo to the endometrium of the uterus
How does the growing embryo/foetus get nutrition?
 The embryo grows inside the mother's womb and gets nourishment
from the mother's blood through the tissue called the placenta.
 Villi on the placenta (embryo side) provides a large surface area
for
 Glucose and oxygen to pass from the mother to the developing
embryo
 Wastes to pass from the embryo to the mother through the placenta
MENSTRUATION:
 Since the ovary releases one egg every month, the uterus also
prepares to receive a fertilised egg every month. Thus, its
lining becomes thick and spongy.
 If the egg is not fertilised, it lives for about one day. Now,
however,
this lining is not needed any longer. So, the lining slowly breaks
and comes out through the vagina as blood and mucous.
 This cycle takes place roughly every month and is known as
menstruation. It usually lasts for about two to eight days.
  First menstruation occurs at the age of 11-14years called monarch
and last menstruation which occurs at the age of 45years called
menopause

Zygote
 It is a fertilized egg formed after the fusion of the sperm with the
egg.
 The zygote divides several times to form an embryo.
Foetus
 It is a state of the embryo that shows all the main recognizable
body parts of a mature organism.
 An embryo gradually develops into a foetus.

REPRODUCTIVE HEALTH
It includes all aspects of which help a person to lead a normal life
STD (sexually transmitted disease)
This is the disease which is spread by sexual contact from an infected
person to a healthy person
They are caused by various microorganisms that live in warm and moist
environments of the vagina, urethra, anus and mouth some common
STDs are –
Gonorrhoea:
Inflammation of the mucous membrane of the urogenital tract,
and rectum, the victim feels a burning sensation and pain during
urination.
Syphilis :
Is caused by a bacterium, which affects the mucous membrane
of the genital, and rectal areas.
AIDS (Acquired Immunodeficiency Syndrome):
AIDS is caused by HIV. It is a fast-spreading incurable disease,
which weakens the body’s immune system.
Modes of transmission of aids
 By having sexual contact with an infected person
 By the transfusion of blood from an infected person
 Through infected needles used for injection
 Through the placenta from the mother of the child during
pregnancy
Warts :
A small bump on the genitals caused by a common sexually
transmitted infection
CONTRACEPTION
 Methods or techniques adopted to prevent pregnancy as a
consequence of sexual intercourse.
Types of Contraceptive Methods :
1. Mechanical/ Barrier Methods
2. Chemical Methods
3. IUCD
4. Surgical Methods
MECHANICAL /BARRIER METHOD
1. Physical devices like condoms (for males & females) and diaphragms
(for females) are examples of this method.
2. These work by preventing the meeting of sperm and ovum.
3. Barrier methods prevent the transmission of Sexually transmitted
diseases by preventing the intermixing of body fluids.
CHEMICAL METHOD
1. These include oral pills and vaginal pills
2. These pills contain certain hormones which works in the following
ways:
● prevent the production of ovum
● kill sperm cells
● prevent implantation
3. These methods have certain side-effects
4. It cannot prevent transmission of STDs
SURGICAL METHOD
VASECTOMY: In a vasectomy, the vas deferens is cut and the ends
joined
 TUBECTOMY
: In tubectomy,
the fallopian
tube is cut and
the two ends are
sealed

MECHANICAL /BARRIER METHOD

1. Physical devices like condoms (for males & females) and diaphragms
(for females) are examples of this method.
2. These work by preventing the meeting of sperm and ovum.
3. Barrier methods prevent the transmission of Sexually Transmitted
Diseases by preventing the intermixing of body fluids
IUCD (Intrauterine Contraceptive Device)
 Other contraceptive devices such
as the loop or the copper-T are
placed in the uterus to prevent
pregnancy.
 Again, they can cause side
effects due to irritation of the
uterus.
 If the vas deferens in the male is
blocked, sperm transfer will be
prevented.
 If the fallopian tube in the female is blocked, the egg will not be
able to reach the uterus.
 In both cases, fertilisation will not take place.
ADVANTAGE OF SURGICAL METHOD
 While surgical methods are safe in the long run,
 Surgery itself can cause infections and other problems if not
performed properly. Surgery can also be used for the removal of
unwanted pregnancies.
 Child sex ratio can be controlled
DISADVANTAGE OF SURGICAL METHOD
 Surgery itself can cause infections and other problems if not
performed properly.
 These may be misused by people who do not want a particular
child, as happens in illegal sex-selective abortion of female
 TEXTBOOK QUESTIONS AND ANSWERS
1. What is the importance of DNA copying in reproduction?
DNA – Deoxyribonucleic acid is the genetic material that is present in
the cells of all organisms. DNA carries genetic information from one
generation to the other, and this helps in producing organisms of its own
types. DNA copying is a must for inheriting the traits from parents. Any
variations in DNA copying will give rise to the origin of new species.
2. Why is the variation beneficial to the species but not necessarily
for the individual?
The reason why the variation is beneficial to the species rather than
individuals is because sometimes the climatic changes have a drastic
effect on the species, which makes their survival difficult. For examples,
if the temperature of the water body increases, there might be certain
species of microorganisms that might die. This may result in a
disturbance in the environment. So, variation is beneficial to species and
not to the individuals.
3. How does binary fission differ from multiple fission?
When a single cell divides into two equal halves, it is known as binary
fission. Bacteria and amoeba are examples of binary fission. When a
single cell divides into multiple daughter cells at the same time, it is
known as multiple fission. Algae and sporozoans are examples of
multiple fission.
4. How will an organism be benefited if it reproduces through
spores?
Following are the ways through which an organism will benefit if it
reproduces through spores:
 Number of spores produced in one sporangium would be large.
 To avoid competition in one place, spores can be distributed to
faraway places with the help of air.
 To prevent dehydration under unfavourable conditions, the spores are
covered by thick walls.
5. Can you think of reasons why more complex organisms cannot
give rise to new individuals through regeneration?
Organisms at higher complex levels cannot give rise to new individuals
through regeneration because they have organization of their organs
system at different levels. All these organ systems are interconnected
and work in full coordination. They can regenerate a few of their lost
body parts like skin, blood, muscles, etc. but can’t give rise to new
individuals.
6. Why is vegetative propagation practised for growing some types
of plants?
The following are the advantages of practising vegetative propagation
for growing some types of plants:
 Crops like oranges, bananas, pineapple do not have viable seeds, so
vegetative propagation can be used.
 It is a rapid, cheap and easier method to grow crops.
 It can be used in places where seed germination fails.
 A good quality of variety can be preserved.
7. Why is DNA copying an essential part of the process of
reproduction?
DNA copying is an essential part of the process of reproduction because
it carries the genetic information from the parents to offspring. A copy
of DNA is produced through some chemical reactions resulting in two
copies of DNA. Along with the additional cellular structure, DNA
copying also takes place, which is then followed by cell division into
two cells

8. How is the process of pollination different from fertilisation?

Pollination
The transfer of pollen grains from the anther of a stamen to the stigma
of a carpel is called pollination.
It takes place by various pollinating agents
Fertilisation
Fertilisation occurs when the male gamete present in the pollen grain
joins with the female gamete (or egg) present in the ovule.
It takes place by natural or artificial means
What is the role of the seminal vesicles and the prostate gland?
 Both the seminal vesicle and prostate gland secrete fluids that form
a part of the semen. The fluid secreted from the seminal vesicle
forms 60% of semen while the fluid secreted from the prostate
gland forms 30% of the semen. It makes the path smooth through
which the sperms travel.
 This fluid protects the sperm from the acids present in the urethra.
 This fluid provides nutrition to sperms in the form of fructose,
calcium and some enzymes.
9. What are the changes seen in girls at the time of puberty?
The various changes that occur in girls at puberty are :
 Hair grows under the armpits and pubic region.
 Mammary glands (or breasts) develop and enlarge.
 The hips broaden.
  Extra fat is deposited in various parts of the body like hips and
thighs.
 The fallopian tube, uterus and vagina enlarge

 Ovaries start to release eggs,

 Menstruation (monthly periods) starts.
 Feelings and sexual drives associated with adulthood begin to
develop.
10. How does the embryo get nourishment inside the mother’s body?
In the mother’s body, the embryo gets nutrition from the mother’s blood.
For this, there is a special structure, called the placenta. Placenta
contains villi. There are empty spaces in the mother’s tissues that cover
the villi. It provides a large surface area for the transfer of glucose,
oxygen and other substances from the mother to the embryo.
11. A woman is using a copper-T. Will it help in protecting her from
sexually transmitted diseases?
Copper-T is a contraceptive method that prevents implantation of the
zygote inside the uterus. It cannot prevent women from sexually
transmitted diseases. These diseases are transmitted by contact which
cannot be prevented by copper-T.
What are the advantages of sexual reproduction over asexual
reproduction?
Advantages of sexual reproduction:
→ In sexual reproduction, more variations are produced. Thus, it ensures
the survival of species in a population.
→ The newly formed individual has characteristics of both parents.
→ Variations are more viable in sexual mode than in asexual one. This
is because, in asexual reproduction, DNA has to function inside the
inherited cellular apparatus.

What are the functions performed by the testis in human beings?

Functions of testes:
→ Produce sperms, which contain haploid set of chromosomes of father.
→ Produce a hormone called testosterone, which brings about secondary
sexual characters in boys.
Why does menstruation occur?
Menstruation is a process in which blood and mucous flows out every
month through the vagina. This process occurs every month because one
egg is released from the ovary every month and at the same time, the
uterus (womb) prepares itself to receive the fertilized egg. Thus, the
inner lining of the uterus gets thickened and is supplied with blood to
nourish the embryo. If the egg does not get fertilised, then the lining of
the uterus breaks down slowly and gets released in the form of blood and
mucous from the vagina.
Draw a labelled diagram of the longitudinal section of a flower.

Answer

What are the different methods of contraception?

The contraceptive methods can be broadly divided into the following
types:
→ Natural method: It involves avoiding the chances of meeting of
sperms and ovum. In this method, the sexual act is avoided from day
10th to 17th of the menstrual cycle because during this period, ovulation
is expected and therefore, the chances of fertilization are very high.
→ Barrier method: In this method, the fertilization of ovum and sperm is
prevented with the help of barriers. Barriers are available for both males
and females. Condoms are barriers made of thin rubber that are used to
cover penis in males and vagina in females.
→ Oral contraceptives: In this method, tablets or drugs are taken orally.
These contain small doses of hormones that prevent the release of eggs
and thus fertilization cannot occur.
→ Implants and surgical methods: Contraceptive devices such as the
loop or Copper-T are placed in uterus to prevent pregnancy. Some
surgical methods can also be used to block the gamete transfer. It
includes the blocking of vas deferens to prevent the transfer of sperms
known as vasectomy. Similarly, fallopian tubes of the female can be
blocked so that the egg will not reach the uterus known as tubectomy.
How are the modes for reproduction different in unicellular and
multicellular organisms?
In unicellular organisms, reproduction occurs by the division of the
entire cell. The modes of reproduction in unicellular organisms can be
fission, budding, etc. whereas in multicellular organisms, specialised
reproductive organs are present. Therefore, they can reproduce by
complex reproductive methods such as vegetative propagation, spore
formation, etc. In more complex multicellular organisms such as human
beings and plants, the mode of reproduction is sexual reproduction.
How does reproduction help in providing stability to populations of
species?
Reproduction is the process of producing new individuals of the same
species by existing organisms of a species, so, it helps in providing
stability to population of species by giving birth to new individuals as
the rate of birth must be at par with the rate of death to provide stability
to population of a species.
11. What could be the reasons for adopting contraceptive methods?
Contraceptive methods are mainly adopted because of the following
reasons:
→ To prevent unwanted pregnancies.
→ To control population rise or birth rate.
→ To prevent the transfer of sexually transmitted diseases.