Sexual reproduction involves the fusion of two gametes - one male and one female. In plants, this occurs through pollination where pollen is transferred from the anther to the stigma, and fertilization where the pollen tube delivers sperm to fuse with the egg. This restores the chromosome number and produces offspring that are genetically different from the parents, allowing for beneficial variations that help species adapt and survive changing environments. Asexual reproduction only involves one parent and mitosis, resulting in genetically identical offspring but lacks variations. Both modes are important - sexual reproduction for variations and asexual for rapid reproduction.

1. Standard/ Grade/ Class 10
Life Cycle (Reproduction)
Gurudatta K Wagh

2. Reproduction
Fundamental characteristic of living
things
Necessary to maintain the number of
individuals of a species and to prevent
their extinction
All living organisms produce new
individuals (new generation) of the same
species

3. Creation of a DNA
copy
• Basic process in
reproduction
• Some variations take
place in this process
each time
• DNA copies
generated are similar
but not identical to
the original

4. Importance of variations
Changes in ecological system can wipe
out a species
But, if variations in some individuals are
suitable for new environment, there is a
chance of survival of that species

5. Modes of reproduction: (A) Asexual, and (B) Sexual
(A) Asexual reproduction
•Only one parent is involved
•Cells divide mitotically
•There is no fusion of two different cells
•The daughter cells produced are genetically
identical to the parent cells
•Disadvantage - Lack of genetic variations
•Advantage - rapid reproduction

6. Mitosis: A type of cell division leading to
growth and development
It occurs in somatic cells (any cell of a living
organism other than the reproductive cells)

7. Modes of asexual reproduction in unicellular organisms
Binary Fission
• Employed by most prokaryotes, some protozoa and some
organelles within eukaryotic cells
• Living cell divides into two equal or nearly equal parts which
have potential to grow to the size of the original one
• The plane of cytoplasmic division is through any plane in
amoeba (simple binary fission)
Amoeba - simple binary
fission

8. Paramoecium - transverse binary fission
Euglena - longitudinal binary fission
In some
organisms
fission occurs
through a
specific axis,
viz.
transverse,
longitudinal

9. Multiple fission
• During unfavourable condition, the amoeba withdraws its
psuedopodia, becomes almost round and secretes a hard
covering called cyst
• Inside the cyst nucleus divides into many nuclei by repeated
division, followed by division of cytoplasm
• Many daughter cells are formed
• The cyst bursts to release the daughter cells during
favourable condition
Amoeba -
Multiple
fission

10. Budding
• In yeast a small outgrowth is formed on the parental cell
• The nucleus of the parental cell divides
• One daughter nucleus migrates into the bud
• The bud increases in size, separates and grows further

11. Modes of asexual reproduction in multicellular
organisms
They have different cell types which perform different
functions
They have special organs, placed at a definite place
in the body which are formed by specific tissues
In such organised organisms method of cell-by-cell
division to reproduce is impractical
They show complex ways of reproduction
The complexity in reproduction increases with the
complexity in structure of organisms

12. Fragmentation
• When water and nutrients are available, spirogyra grow and
multiply rapidly
• The filament of spirogyra undergoes fragmentation resulting
in numerous filaments
• With cell enlargement and subsequent mitosis, each
fragment grows and develops into a mature filament
Spirogyra

13. Regeneration
• Some animals can reconstruct the entire body
from the isolated body cells
• Regeneration is carried out by specialised cells
• These cells proliferate and make large number of
cells which later develop into various cell types
and tissues and help in production of new
organism
• When Planaria is cut into many pieces, each piece
develops into a whole Planaria

14. Planaria
• Regeneration occurs
only if the planarial
body gets cut into
pieces
• But animals cannot
wait to be cut to
reproduce
• So regeneration is
not the same as
reproduction

15. Budding
• Hydra uses regenerative
cells for reproduction in the
process of budding
• When Hydra reaches maturity and is well fed, its
body wall begins to form a rounded growth (bud)
from the stalk of the adult
• The bud develops into a miniature hydra

16. Hydra
• The body layers, body cavity and the digestive cavity of
the young hydra are continuous with that of the parent
hydra
• The young hydra gets nourishment from the parent
• When the young hydra is sufficiently developed to take up
an independent existence, the base of the new hydra
seals off and thus allows the new individual to break off
from the parent hydra

17. Vegetative Propagation
New plants are produced from the vegetative parts
(roots, stems, leaves and buds)
e.g. potato plant develops from eyes (buds on
potato), Bryophyllum reproduces from the buds on
the leaf margin, the roots of sweet potato give rise to
new plants, etc.

18. Features of vegetative propagation
• Plants are similar to the parent, as they are
produced from a single parent
• Plants take less time to grow and bear flowers and
fruits earlier than those produced from seeds

19. Spore formation
The hyphae of bread
mould (Mucor) are
thread like structures
The mould forms
spores inside a
sporangium
When the spores are ready to leave the sporangium,
it breaks open. If they land in a moist place, they
germinate to form new mould

20. Cloning
Animal cloning is the process by which
an entire organism is reproduced in a
genetically identical manner, from a
single cell taken from the parent
organism
This means the cloned animal is an exact duplicate of
its parent in every way. It has the DNA which is
identical to parent DNA
e.g. Dolly sheep was the first mammal to be cloned
from an adult cell rather than an embryo

21. (B) Sexual reproduction
• Two parents are involved in sexual reproduction,
one male and the other female
• The two main processes involved in sexual
reproduction are 1) Meiosis, and 2) Fertilization

22. (1) Meiosis: Halving the number of chromosomes -
from 2n to n - takes place resulting in the formation of
haploid gametes

23. (2) Fertilization: It is a process in which the male
gamete fuses with the female gamete resulting in the
formation of diploid zygote. It restores the number of
chromosomes (2n)

24. Features of sexual reproduction
• There is fusion of two germ cells
• Offsprings produced by sexual reproduction are
different from parents
• Variations give rise to variety and diversity
• Variation enables organisms to adapt and survive
in the changing environment
• It helps to prevent the complete extinction of
animal and plant species

25. Sexual reproduction in plants
Flower is a functional unit concerned with sexual
reproduction

26. Carpel: Present in the centre of flower.
Made up of three parts - stigma, style
and ovary
Stigma: Sticky terminal part of the
style. Receptive organ on which pollen
germinates
Female reproductive part of a flower
Style: Elongated part of carpel bearing stigma at its
tip
Ovary: The swollen lower part of carpel containing
one or more ovules. Each ovule has an egg cell
(female germ cell)

27. Stamen: Made up of two parts anther and filament
Anther: Usually bilobed and produces pollen grains.
Male germ cells are produced by pollen grains
Filament: Stalk of anther
Male reproductive part of a flower

28. Pollination
Involves the transfer of pollen grains from anther to
stigma

31. Fertilization
• After the pollen grain lands on the
stigma, it germinates
• The pollen tube grows out from a
pollen grain
• It travels through the style to reach
the ovary
• Each pollen tube contains two male
gametes and releases them near
the egg
• One male gamete fuses with the egg cell to form zygote
• The second male gamete fuses with the secondary nucleus
in the embryo sac to form endosperm
• This is called as double fertilization
• The zygote develops into embryo and the endosperm serves
as nutritive tissue for the growing embryo
• This embryo is capable of growing into a new plant

32. Fertilization

33. •The ovule develops into a seed and ovary develops
into the fruit
•The seed contains the future plant
•It develops into the seedling under appropriate
conditions
•This process is known as germination
Germination
•After fertilization,
the zygote divides
several times to
form an embryo
within the ovule

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