The document discusses various modes of reproduction in organisms. It explains that reproduction allows for the survival and increase of species by producing new individuals. It describes asexual reproduction methods like binary fission, budding, regeneration, fragmentation, and spore formation which involve a single parent. Sexual reproduction involves two parents. The document also discusses the importance of variation during reproduction for species survival and evolution.

1. CH-8:- HOW DO ORGANISMS
REPRODUCE?
• CLASS:- X
• SUB:- SCIENCE
PART:- 1

2. Reproduction :-
Reproduction is the process by which living organisms
produce new individuals of the same species from the
existing organisms.
Reproduction is necessary for the survival and increase in
the population of a species. If organisms do not reproduce,
their population decreases and species will become extinct.
Do organisms create carbon copies ofthemselves ?
 The DNA (Deoxyribo nucleic acid) molecules in the
chromosomes in the nucleus is responsible for the
transfer of characters from the parents to the off springs.
 During reproduction the reproductive cells produce two
copies of the DNA which separate into two cells.
 The DNA copies will be similar but not identical to each
other. So the new individuals have slight variations from
their parents. This is the basis for variations and
evolution of new species.

3. 3) The importance of variation :-
DNA copying during reproduction is important for
maintaining the body designs of different organisms to
survive in the existing environment. But the environment
constantly changing due to changes in temperature, climate,
water levels etc. If organisms cannot adjust themselves to
the changes in the environment then their species will
become extinct.
 If there are variations in some individuals of a species
they may be able to survive the changes in the
environment.
Eg. Moth:- White colour Moth was easily visible to eagle and
were hunted but black colour Moth was not visible, so they
were protected. Because of this variation, black one was
able to survive due to variation.
 So variations in species is necessary for the survival of
different species and for the evolution of new species.
is

4. • Germ cells:- Cells that create
reproductive cells (gametes).
• Gamete:- It is a haploid cell that
fuses with another haploid cell
during fertilization in organisms that
sexually reproduce.
 Male gamete:- Sperm
 Female Gamete:- OVA
• Karyokinesis:- Process of division of a
cell's nucleus during the cell division
processes like mitosis and meiosis.
• Cytokinesis: Process of cell division,
which divides the cytoplasm of a
parental cell into two daughter cells.
• Zygote:-First diploid cell that forms
after the fusion of male and female
gamete.

5. 4) Types of reproduction :-
There are two main types of reproduction in living organisms. They
are asexual reproduction and sexual reproduction.
Asexual reproduction :- is reproduction in which new individuals
are produced from a single parent.
Sexual reproduction :- is reproduction in which two individuals
are involved to produce a new individual.
Asexual reproduction is of different types. They are:- fission,
budding, regeneration, fragmentation, spore formation, vegetative
propagation etc.

6. ASEXUAL REPRODUCTION

7. i) Fission :-
Fission is an asexual reproduction by which a unicellular
organism divides and forms two or more new individuals.
Fission is of two types. They are binary fission and multiple
fission.
i) Binary fission :- In this method an organism divides and
forms two individuals. First the nucleus divides and forms
two nuclei. Then the cytoplasm divides and forms two
daughter cells. Eg:- Amoeba, Paramaecium etc.
ii) Multiple fission :- In this method one organism divides
into many daughter cells. Eg.Plasmodium (Malarial parasite).

8. Multiple Fission in Plasmodium
• Plasmodium is the malarial parasite (protozoan) which causes malaria
disease in human beings.
• Spread by the female Anopheles mosquitoes from person to person.
• Single parent splits to form many new organisms at the same time.
 Particularly in unfavourable condition, a cyst or protective wall is
formed around the cell of a single-celled organism (like Plasmodium
shown in figure).
 Inside the cyst, nucleus of cell splits several times to form many smaller
nuclei called daughter nuclei.
 Little bits of cytoplasm collect around each daughter nuclei and thin
membranes are formed.
 When the favourable conditions arrive, the cyst breaks open and the
many daughter cells present in it are released, each forming a new
organism.

11. ii) Budding :-
In this 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.
bud

12. iii) Regeneration :-
In this method a part of the body if the organism if cut or
broken can develop into a new individual. Eg :- Hydra,
Planaria, Star fish etc.
Note:- Regeneration is not exactly the same as reproduction because most simple animals
would not depend on being cut into pieces to be able to reproduce.

13. Process of Regeneration
• Regeneration of an organism from its cut
body parts occurs by the process of
growth and development. The process
are:
 The cells of cut body part of the organism
divide rapidly to make a ball of cells.
 The cells present in the ball of cells move
to their proper places within the ball
where they have to form various organs
and body parts of the organism.
 The cells then change their shapes or
become specialized to form different
types of tissues.
 These different tissues form various
organs and body parts of the organism.
 In this way a complete organism is
regenerated.

14. iv) Fragmentation :-
In this method the body of a simple multicellular
organism breaks up into smaller pieces on maturation and
each fragment develops into new individuals.
Eg :- Spirogyra., Sea Anemones

15. v) Spore formation :-
In this method structures called sporangia produce tiny
cells called spores. When the spores come in contact with a
moist surface, it develops into new individuals.
Eg :- Rhizopus , Mucor, Penicillium etc.

16. vi) Vegetative propagation :-
In this method new plants are produced from the vegetative parts of
the plant like root, stem or leaf. Eg:- from roots – dhalia, sweet potato,
from stem – potato, ginger, from leaf – bryophyllum, begonia.
Plants produced by vegetative propagation produce flowers and
fruits earlier than those produced from seeds. It also helps in the
propagation of plants which do not produce seeds like rose, jasmine
banana etc.
Vegetative propagation can also be done artificially by cutting,
layering, grafting etc.

17. Benefits of Vegetative Propagation
• Plants can bear flowers, fruits earlier than those
produced from seeds.
• Growing plants like Banana, Orange, rose, Jasmine
etc. have lost the capacity to produce seeds.
• Genetically similarity is maintained in the plants.
• Help in growing seedless fruits.
• Cheaper and easier method of growing plants.

18. Artificial Propagation of Plants
• The process of growing many plants from
one plant by man-made methods .
• Three commonly used methods are:-
1. Cuttings
2. Layering
3. Grafting and Buddings

19. 1. Cuttings
• A cutting is a piece that has been cut off a mother plant and then caused
to grow into a whole plant.
• Often this involves a piece of stem that is treated with hormones to
encourage new roots to form before planting.
• Sometimes root cuttings with buds on them will produce new shoots
when pressed directly into soil.
• While making a cut care should to taken to see that there are some buds
on it.
• The new plant formed from a cutting is exactly similar to the parent plant.
• Eg:- Rose, Sugarcane, Bananas, Cactus etc.

20. 2. Layering
• In this method, branch of a plant is pulled towards the ground
and part of it is covered with moist soil leaving the tip of the
branches exposed above the ground.
• After some days, new roots develops from the part of the
branch buried in the soil.
• The branch is then cut off from the parent plant.
• The part of the branch which has developed roots grows to
become a new plant like parent plant.

21. 3. Grafting or Budding
• Grafting and Budding are horticultural techniques used to join
parts from two or more plants so that they appear to grow as a
single plant.
 Stock:- The cut stem of a plant (or tree) having roots (fixed in soil)
 Scion:- The cut stem of another plant (or trees) without roots. It
may have leaves on it.
• In grafting, the upper part (scion) of one plant grows on the root
system (rootstock) of another plant.
 Eg. Apple, Peach, Pear Tree, Rose etc.
• In the Budding process, a bud is taken from one plant and grown
on another.
 Trees propagated through budding include Dogwood,
Birch, Maple, Mountain Ash, Redbud and Ginko etc.

22. Grafting Budding

23. Advantages of Grafting
• It enables us to combine the most desirable
characteristics of the two plants (scion and stock) in
its flowers and fruits.
• By this method, a very young scion (shoot part of the
plant) can be made to flower and produce fruits
quite fast when it is grafted to the stock (stem having
roots) of a mature plant.
• It enables to obtain flowers and fruits having
different desired characteristics by grafting scions
from different varieties of plants on the same stock.
• Grafting can be used to produce varieties of seedless
fruits.

24. Disadvantages of grafting and Budding:
• New varieties cannot be developed.
• These are extensive methods of propagation.
They require specialized skill.
• The life span of grafted and budded plants is
short as compared to seed propagated plants.
• Spread of viral diseases may occur through this
method.

25. Advantages of Artificial Vegetative Propagation
• The new plants produced will be exactly like the parent
plants.
• Any desirable features of the parent plant will be
replicated in the new plants.
• Fruit trees grown from cutting or by grafting start to bear
fruits much earlier then trees grown from seeds.
• The plants need less attention in their early years then
the plants grown from seeds.
• Many plant can be grown from just one parent plant by
artificial propagation.
• Seedless plant can also be grown.

26. Disadvantages of Artificial Vegetative
Propagation
• Lack of dispersal mechanism lead to
overcrowding.
• New Plants are less varied.
• New Plants may be less adaptable to changes in
environmental condition.
• Disease of the parent plant can easily be
transmitted to the offspring.

27. Tissue Culture
• A method of biological research in which
fragments of tissue from an animal or plant are
transferred to an artificial environment in which
they can continue to survive and function.
• The cultured tissue may consist of a single cell, a
population of cells, or a whole or part of an organ.
• Cells in culture may multiply; change size, form, or
function; exhibit specialized activity (muscle cells,
for example, may contract); or interact with other
cells.

28. Process of Tissue culture in Plants
• A small piece of plant tissue is taken from the
growing point of the plant (tip of the plant) and
placed on a sterile jelly which contains nutrients
and plant hormones.
• The hormones make the cells in the plant tissue to
divide rapidly producing many cells which form a
shapeless lump of mass called callus.
• The callus is then transferred to another jelly
containing suitable plant hormones which
stimulate the callus to develop roots.

29. • The callus with developed
roots is then put on a yet
another jelly containing,
different hormones which
stimulate the development of
shoots.
• The callus having roots and
shoots separates into tiny
plantlets. In this way, many
tiny plantlets are produced
from just a few original plant
cells or tissue.
• The plantlets thus produced
are transplanted into pots or
soil, where they can grow to
form mature plants.

30. Advantages of Tissue Culture
• The new plantlets can be grown in a short amount of
time.
• Only a small amount of initial plant tissue is required.
• The new plantlets and plants are more likely to be free of
viruses and diseases.
• The process is not dependent on the seasons and can be
done throughout the year.
• You need only a relatively small space to perform the
process (ten times the plants in one-tenth of the space).
• On a larger scale, the tissue culture process helps to
supply the consumer market with new subspecies and
variety.

31. Disadvantages of Tissue Culture
• The setting up of a plant tissue culture laboratory is very
expensive including it’s machines and reagents.
• The experiment of tissue culture must be handled by highly
trained people as the procedures requires special care and
careful observations.
• If all the plants are genetically similar, there is reduction in
genetic diversity.
• If a plant is susceptible to disease, all the plants of this cloned
stock will share this undesirable trait and be susceptible to that
particular disease.
• The procedures depends on the type of species being cultured,
hence there is need for trail and error method for any new
species if there is no review about that species.
• If precautions are not taken, the whole stock may be
contaminated or infected.