1- REPRODUCTION IN ORGANISMS
CHAPTER NO.1 REPRODUCTION TYPES OF
REPRODUCTION
A1
LIFE SPAN
The period from birth to the natural death of an
organism represents its life
span.Life spans of organisms are not necessarily
correlated with their
sizes.Whatever be the life span, death of every
individual organism is a certainty i.e. no individual is immortal, except
single-celled organisms.There is no natural death in single-celled organisms as
they divide and form 2 new cells.
REPRODUCTION
Reproduction means to reproduce. It is a biological
process by which an organism reproduces an offspring who is biologically
similar to the organism. Reproduction enables and ensures the continuity of
species,generation after generation. It is the main feature of life on
earth.Let us have a detailed overview of reproduction, its types and the modes
of reproduction in plants and animals.
There are basically two types of reproduction:
1. Asexual Reproduction
2. Sexual Reproduction
SEXUAL REPRODUCTION
Sexual reproduction is a type of reproduction that involves the production
of an offspring by the fusion of male and female
gametes.”
For example: reproduction in Humans.
ASEXUAL REPRODUCTION
Asexual reproduction refers to the type of
reproduction in which only asingle organism gives rise to a new individual.For
example budding in Hydra.
Q1. “The offsprings produced by asexual
reproduction are
referred to as clones”. Why?
A1. During asexual reproduction, there is no fusion
of gametes and a single parent divides and re-divides to produce the
offsprings. Hence, the offsprings are morphologically and genetically similar
to the parents and therefore referred to as clones.
Q2. Why can’t multicellular organisms
reproduce by cell division?
A.2. cell division takes place in the body of a
multicellular organism but it
does not aid in reproduction. Every day millions of
cells die and are replaced by others. Multicellular organisms have
well-developed reproductive organs that carry out the reproduction process.
Q.3.What is Sexual Reproduction?
A.3. see page no 3 of assignment
Q4.What is Asexual Reproduction?
A.A. see page no 4 of assignment.
A2
ASEXUAL REPRODUCTION
Does not involve the fusion of gametes or change in
the number of chromosomes.
Offspring that arise by from either unicellular or
multicellular organisms
inherit the full set of genes of their single
parent.
What is Asexual Reproduction?
Asexual reproduction is a mode of reproduction in
which a new offspring is
produced by a single parent. The new individuals
produced are genetically and
physically identical to each other, i.e., they are
the clones of their parent.
Asexual reproduction is observed in both
multicellular and unicellular organisms.
This process does not involve any kind of gamete
fusion and there won't be any
change in the number of chromosomes either. It will
inherit the same genes as the
parent, except for some cases where there is a
chance of rare mutation to occur.
Characteristics of Asexual Reproduction
Following are the important features of
asexual reproduction:
1. Single parent involved.
2. No fertilization or gamete formation takes place.
3. This process of reproduction occurs in a very
short time.
4. The organisms multiply and grow rapidly.
5. The offspring is genetically similar.
TYPES OF ASEXUAL REPRODUCTION
There are different types of asexual
reproduction:
1. Binary Fission The term
“fission” means “to divide”. During binary fission, the parent cell divides
into two cells. The cell division patterns vary in different organisms, i.e.,
some are directional while others are non-directional. Amoeba and euglena
exhibit binary fission.It is one of the simplest and uncomplicated methods of
asexual reproduction. The parent cell divides into two, each daughter cell
carrying a nucleus of its own that is
genetically identical to the parent. The cytoplasm
also divides leading to two equal-sized daughter cells. The process repeats
itself and the daughter cells grow and further divide.
2. Fragmentation
Fragmentation is another mode of asexual reproduction exhibited by
organisms such as spirogyra, planaria etc. The
parent body divides into several
fragments and each fragment develops into a new
organism.
3. Regeneration
Regeneration is the power of growing a new organism
from the lost body part. For
eg., when a lizard loses its tail, a new tail grows.
This is because the specialized
cells present in the organism can differentiate and
grow into a new individual.Organisms like hydra and planaria exhibit
regeneration.
4.Budding
Budding is the process of producing an individual through the buds that develop
on the parent body. Hydra is an organism that reproduces by budding. The bud
derives nutrition and shelter from the parent organism and detaches once it is
fully grown.
5. Spore Formation
Spore formation is another means of asexual reproduction.
During unfavourable conditions, the organism develops sac-like structures
called sporangium that
contain spores. When the conditions are favourable,
the sporangium burst opens
and spores are released that germinate to give rise
to new organisms.
IMPORTANT QUESTIONS
Q.1. What are the two inherent
characteristics of amoeba and yeast that
favour asexual reproduction in them?
A.1. The two inherent properties of amoeba that help
them to reproduce asexually are:
1. They have relatively simple structures and can
divide very quickly.
2. They are uniparental
Q.2. Differentiate between binary fission
and multiple fission.
A.2.Binary Fission:
1. In this type of fission, the parent cell gives
rise to two daughter cells.
2. It is expressed by organisms like amoeba,
paramecium, etc.
Multiple Fission:
1. In this type of fission , the parent cell gives
rise to more than two
daughter cells.
2. It is expressed by organisms plasmodium.
A3
SIMPLIFIED NOTES
VEGETATIVE PROPAGATION:Vegetative
propagation is an asexual method of plant reproduction that occurs in its
leaves, roots and stem. This can occur through fragmentation and regeneration
of specific vegetative parts of plants.Let us explore the different types of
vegetative propagation and its examples in detail.
TYPES OF VEGETATIVE PROPAGATION
Different types of vegetative propagation include:
Natural Vegetative Propagation:This occurs when
plants grow and develop naturally without any human interference. Natural
vegetative propagation can be enabled by the development of adventitious roots.
Thus, new plants may emerge from the
roots, stem and leaves of the parent plant.
The vegetative plant structures arising from the
stem are known as rhizomes, bulbs, runners, tubers, etc. The plants propagated
vegetatively
are given below:
1. Stem:
Runners grow horizontally above the ground. The buds are formed at the nodes of
the runners.
2. Roots:
New plants emerge out of swollen, modified roots known as tubers. Buds are
formed at the base of the stem.
3. Leaves:
Leaves of a few plants get detached from the parent plant and develop into a
new plant.
4.Bulbs:
Bulbs have an underground stem to which the leaves are attached. These leaves
are capable of storing food. The centre of the bulbcontains an apical bud that
produces leaves and flowers. Shoots are
developed from the lateral buds.
Artificial vegetative propagation:This is a type of
vegetative reproduction carried out by humans on the fields and laboratories.
The most common types of vegetative reproduction occurring artificially
include:
1. Cutting:
In this, a part of a plant, specifically a stem or leaf is cut and
planted in the soil. These cuttings are sometimes
treated with hormones to
induce root development. The new plant is formed
from the adventitious roots developing from the cutting.
2. Grafting:
In this, the cutting from some other plant is attached to the stem of plant
rooted in the ground. The tissues of the graft become integrated with the
tissues of the rooted plant and develop as a single plant over time.
3. Layering:
In this, the stem of the plant is bent to the ground and covered with soil.
Adventitious roots emerge from the plant parts covered with the soil. This
attached stem with developing roots is known as a layer.
4. Tissue Culture:
In this, the plant cells from different parts of a plant are
cultured in the laboratory to develop a new plant.
This technique is helpful in increasing the number of rare and endangered plant
species that are
unable to grow under natural conditions.
LET US KNOW WHAT WE LEARN ?
(A) Very Short Answer type Questions:-
MCQ
1. which one of the following plant is
propagated through air layering
(a) apple
(b) cherry
(c)Litchi
(d)grapes
Ans. (c) ( Apples and cherry are mostly propagated
by shield budding, Grapes are
propagated by cutting)
2. Name a method in which the cut stems of
two different plants are joined together to grow as a single plant?
(a) Layering
(b) Grafting
(c)Cutting
(d)None of the above
Ans. (b) (During layering and cutting only one
plants involved but during grafting
two plants are joined together to grow as a single
plant)
4. Name the method of asexual reproduction
in plants in which callus is produced?
(a)Regeneration
(b)Micro propagation
(c)Fragmentation (
d)Vegetative Propagation
Ans. (b) ( Micropropagation refers to the invitro
multiplication of plant material to
produce millions of plants for transfer to the
fields.Other methods are used for
production of single plant at a time )
4. In which artificial propagation method
Stock and Scion are involved?
(a) Tissue Culture
(b) Cuttings
(c) Grafting
(d) Layering
Ans. (c) (Tissue culture means different parts of a
plant are cultured in the
laboratory to develop a new plant. Cutting means a
part of a plant, specifically a
stem or leaf is cut and planted in the soil.Layering
means the stem of the plant is bent to the ground and covered with soil.)
5. In China rose plant which method of
artificial propagation is used?
(a) Cuttings
(b) Layering
(c) Grafting
(d)Tissue Culture
Answer:(b)
True /False:-
1.Vegetative propagation by leaf takes place in
rose.
Answer (False )
2. Bulbs have an underground stem to which the
leaves are attached
Answer (true)
Fill in the Blanks:-
1.The production of new individuals from the
vegetative part of the parent is
called .
Answer:-Vegetative propogation
2.Types of vegetative propagation cutting is found
in and grafting is found in
Answer :-sugarcane and Mango
(B) Short Answer type Questions:-
Q.1. Write the significance of vegetative
propagation.
Q.2.What type of modification are ginger, potato,
onion and Samarkand?
Q.3.Give examples of plants which are propagated
vegetatively from underground stems and creeping stems.
(C) Long Answer type Questions:-
Q.1.List various artificial methods of vegetative
propagation with examples.
A4
SIMPLIFIED LEARNING MATERIAL
Sexual Reproduction:In this mode of reproduction, a
new offspring is produced by the participation of two parents of the opposite
sex. This type of reproduction is
seen in all multicellular organisms including birds,
reptiles, dog, cat, cattle’s,elephants, etc. There are three phases of living
organisms
1.Juvenile Phase/Vegetative Phase:It
is pre-reproductive phase in the life cycle of an individual. It is the period
of growth between the births of an individual up to reproductive
maturity.Juvenile phase is known as vegetative phase in plants. This phase is
of different durations in different organisms.
2. Reproductive Phase (Maturity Phase):
The organisms reproduce offspring during this phase.
Reproductive organs develop and mature during this period which is called
puberty. Appearance of flowers in higher plants indicates sexual maturity.
3. Senescent Phase (Senescence,
Ageing):
It begins from the end of the reproductive phase.
The terminal irreversible stage of ageing is called senescence. This is the
last phase of life span,senescence ultimately leads to death.
The three events that take place during the sexual
reproduction
1. Pre-Fertilization Events:All
the events of sexual reproduction that take place before the fusion of gametes
are included in this category. Two main pre-fertilisation events are
gametogenesis (formation of gametes) and gamete transfer
(i) Gametogenesis:The
process of formation of male and female gametes is called
gametogenesis. Gametes are haploid cells. Organisms such as monerans, fungi, algae and bryophytes have haploid parental body.Such type of organisms produce gametes by mitotic division and if the parent body is diploid; gametes are formed by meiosis.
When male and female gametes are similar appearance
and it is not possible to differentiate them into male and female gametes, they
are called homogametic or isogametes. If the male and female gametes are
morphologically dissimilar they are called heterogametes. Among heterogametes,
the male reproductive unit is called antherozoid or sperm and female reproductive unit is known as egg or ovum.
grows downwards through the style until it reaches
to ovule situated in the ovary. On reaching the ovule, pollen tube enters into
it and then releases male gametes near the egg.
In dioecious animals; male and female gametes are
formed in different individuals. Hence, such organisms need to evolve a special
mechanism for gamete transfer. Fertilization is the most critical event in
sexual reproduction, and successful transfer of gametes is necessary for this
event to materialize.
1. Fertilisation:The
process of fusion of male gametes with the female
gametes is called fertilisation or syngamy. It results in the formation of
During the sexual reproduction, the events which
take place after the
formation of zygote are called post-fertilisation
events.
Fertilisation leads to the formation of a diploid
cell called zygote. It is the
vital link that ensures the continuity of species
between the organisms of
one generation and of the next.
Development of zygote depends on:
(a) Type of life cycle of the organism.
(b) Environment it is exposed.
The process of development of embryo from the zygote
is called
embryogenesis,
Embryogenesis involves the following
process:
(a) Cell division to increase in number of cells.
(b) Cell enlargement or growth to increase in
mass/volume of living matter..
(c) Cell differentiation for the formation of
different types of tissues
Embryogenesis in Animals:
Based on whether the development of the zygote takes
place outside or
inside the body of the female parent, animals are
divided into two categories
(i) Oviparous:Those
animals, in which development of zygote takes place
outside the female parent, are called oviparous.
They lay fertilised eggs
covered with hard calcareous shell in a safe place
in the environment, e.g.,a diploid zygote.
In animals, there are two types of fertilization,
internal and external.
Internal fertilization happens in the female body.
External fertilization
happens outside of the body. Mammals, birds, and
reptiles use internal
fertilization.Amphibians and most fish use external
fertilization.
3.Post-Fertilisation Events:During
the sexual reproduction, the events which take place after the formation of
zygote are called post-fertilisation events.
Fertilisation leads to the formation of a diploid
cell called zygote. It is the
vital link that ensures the continuity of species
between the organisms of one generation and of the next.
Development of zygote depends on:
(a) Type of life cycle of the organism.
(b) Environment it is exposed.
The process of development of embryo from the zygote
is called embryogenesis,
Embryogenesis involves the following
process:
(a) Cell division to increase in number of cells.
(b) Cell enlargement or growth to increase in
mass/volume of living matter..
(c) Cell differentiation for the formation of
different types of tissues
Embryogenesis in Animals:Based
on whether the development of the zygote takes place outside or inside the body
of the female parent, animals are divided into two categories
(i) Oviparous:Those
animals, in which development of zygote takes place
outside the female parent, are called oviparous.
They lay fertilised eggs
covered with hard calcareous shell in a safe place
in the environment, e.g.,
reptiles and birds. After a period of incubation,
the young ones hatch out
from the egg.
(ii) Viviparous:The
animals in which the development of zygote takes place into a young one inside
the body of the female parent, are called viviparous. In viviparous animals
placenta develops during pregnancy. The umbilical cord connects
the placenta to your baby. Blood from the mother
passes through the placenta, filtering oxygen, glucose and other nutrients to
your baby via the umbilical cord. The placenta also filters out substances that
could be harmful to your baby and removes carbon dioxide and waste products
from your baby’s blood.After attaining a certain stage of growth, the young
ones are delivered out of the body of the female organism.After childbirth the
process of milk secretion from the mammary glands of a mother start. The milk,
thus produced provides nutrition and immunity to the young one.this process is
called lactation.
Embryogenesis in Plants:In all flowering plants, the
zygote is formed inside the ovule. In most of the plants, with the formation of
zygote, all the parts of the flower except the pistil wither and fall off. In
ovule, the zygote divides several times to form an embryo.Meanwhile the wall of
the ovule becomes hard and it develops into seed. With these developments, the
wall of the ovary also starts to swell. As
a result, the ovary develops into fruit. A thick
wall that covers fruit is called
pericarp. It is protective in function. When seeds
mature, they are dispersed.
Under favourable conditions,
LET US KNOW WHAT WE LEARN ?
(A) Very Short Answer type Questions: -
MCQ
1. The external fertilization found in
which of following living organism?
(a) mammals
(b)amphibians
(c) birds
(d)reptiles
Ans. b ( External fertilization means fertilization
of female egg by male
sperm in outside of body this is the unique features
of Phylum Amphibia)
2. Human beings have how many chromosomes
in each cell?
(a) 26 chromosomes
(b) 46 chromosomes
(c) 23 chromosomes
(d) 48 chromosomes
Ans. b ( 26 chromosome in frog and 48 chromosome in
Gorilla and 23 chromosome in Haploid gametes sperm or ovum)
3. Which one of the following is diploid
structure ?
(a) egg cell
(b) sperms
(c) somatic cell
(d) none of the above
Ans. c ( Egg cell and sperms are haploid cells)
4. In animals, juvenile phase is followed
by,
(a) reproductive phase
(b) senescent phase
(c) old age
(d) vegetative phase
Ans a ( juveline phase means period of growth before
it meet reproductive maturity)
5. Which of the following organisms has the
highest number of chromosomes in each cell?
(a) Housefly
(b) Butterfly
(c) Ophioglossum
(d) Onion
Answer:(c) (housefly having 12 no of chromosomes
Butterfly having 380 , Onion having 32 and Ophiglossum having 1260 no of
chromosomes)
True /False
1. Mitotic cell divisions occur during
embryo-genesis. [True]
2.Gametes are always haploid and gametogenesis always involves meiosis.
[False]
3. The animals in which the development of zygote
takes place into a young one inside the body of the female parent, arc called
viviparous
Q.3. List the events occur during pre fertilization.
[ true]
Fill in the Blanks:-
1. If the male and female gametes are
morphologically dissimilar they are
called (heterogametes)
2. Gametogenesis and gamete transfer
are__sevvennts.. (Pre-fertilisation)
(B) Short Answer type Questions:-
Q.1. Why large number of the gametes produced in the
organisms during external fertilization?
Q.2.What do you mean by juveline phase?
Q.3.What is gametogenesis?
(C) Long Answer type Questions:-
Q.1. State the difference between oviparous and
viviparous animals.
Q.2. What are the changes that take place in an
angiosperm after pollination and fertilization have occurred?
