Reproduction in organisms

1. REPRODUCTION IN
ORGANISMS CLASS
XII
ASEXUAL MODE OF REPRODUCTION

2. REPRODUCTION
 Reproduction is defined as a biological
process in which an organism gives rise to
young ones (offspring) similar to itself.
 The offspring grow, mature and in turn produce
new offspring. Thus, there is a cycle of birth,
growth and death. Reproduction enables the
continuity of the species, generation after
generation.

3. Life span
 The period from birth to the natural death of an
organism represents its life span.
 Figure 1.1 Approximate life spans of some
organisms (NCERT XII) page no.

5. S. NO. ORHANISMS LIFE SPAN
1 Mayfly 24 hours
2 Elephant 70 years
3 Dog 20-30 years
4 Butter fly 1-2 weeks
5 Banana tree 25 years
6 Cow 20-25 years
7 Rose 5-7 years
8 Horse 60 years
9 Fruit fly 30 days
10 Tortoise 100-150 years
11 Parrot 140 years
12 Crocodile 60 years

6. REPRODUCTION
 Based on whether there is participation of one
organism or two in the process of reproduction, it
is of two types.
 Asexual Reproduction- When offspring is
produced by a single parent with or without the
involvement of gamete formation, the reproduction
is asexual.
 Sexual Reproduction-When two parents
(opposite sex) participate in the reproductive
process and also involve fusion of male and
female gametes, it is called sexual reproduction.

7. REPRODUCTION TYPES
 In broad sense we can classify the
reproduction in various types:
 1.Asexual
 2.Vegetative
 3.Parthenogenesis.
 4.Sexual

8. What is Asexual Reproduction?
 Only one parent is involved.
 Offspring are genetically identical to their
parents.
 All cells that come from a single cell are
genetically identical to it and to each other;
they are all clones.
 Single individual (parent) is capable of
producing offspring.
 The offspring are not only Identical also exact
copies of their parent.

9. Types of Asexual Reproduction
1. Mitosis - is the exact
duplication of the
nucleus of a cell so as
to form two identical
nuclei during cell
division.

10. Types of Asexual Reproduction
2. Binary Fission -
occurs in one-celled
organisms such as the
ameba and
paramecium. The
nucleus divides by
mitosis and the
cytoplasm divides,
forming 2 new
daughter cells of equal
size.

11. Types of Asexual Reproduction
3. Budding - Occurs in Hydra
and yeast. The division of
cytoplasm is unequal so one of
the daughter cells is larger
than the other. The daughter
cells can separate or remain
attached.

12. Types of Asexual Reproduction
4. Sporulation - occurs
in molds, mosses, etc
 Spores are produced
in large numbers by
mitosis.
 Spores are
surrounded by a
tough coat to help
them survive harsh
environmental
conditions.

13. Spores
 Encdospores –Some bacteria produce resting
spores by forming of hard impearmeable coat.
 Zoospores -The most common structures are
zoospores that usually are microscopic motile
structures produce by zoosporangium.Ulothrix
 Aplanospores-Unicellular,non-motile,non-
flagellate by sprongium.eg Mucor

14. Spores
 Conidium –Non-motile spores singly or in
chain from the tip of conidiophores.eg
Penicillium.
 Chlamydospore-Non-motile,unicellular,non-
motile,thick walled resting spores.eg
Fusarium.
 Akinete –Enlarge cell of filamentous algae due
to storage of food and thick walled structure.eg
Nostoc

15. Asexual reproductive structures: (a) Zoospores of Chlamydomonas; (b) Conidia of
Penicillium; (c) Buds in Hydra; (d) Gemmules in sponge

16. Types of Asexual Reproduction
5.Regeneration -
Refers to the
replacement or
regrowth of lost
or damaged
body parts

17. Some of these
animals can also
grow new
organisms from
the severed
pieces
(Segmented
Worms and Sea
Stars)

18. Types of Asexual Reproduction
6.Vegetative
Propagation –
Occurs only in plants
(vegetative). New
plants develop from
the roots, stems, or
leaves of the parent
plant.

19. vegetative propagation( Natural methods)
Vegetative propagation grouped into two different
methods: Natural and Artificial. Natural methods are
such as
 Leaf
 Runner
 Rhizome
 Sucker
 Tuber
 Bulb and
 Offset
These structures are called vegetative propagules.

20. Vegetative propagule (a) Eyes of potato; (b) Rhizome of ginger; (c) Bulbil
of Agave; (d) Leaf buds of Bryophyllum; (e) Offset of water hyacinth

21. Runners
Runners are side shoots
which grow out from the
parent plant.
Buds form at points along the
runner and eventually these
buds form roots and grow into
new plants.
Examples: spider plant
(Anthericum), strawberry
(Fragaria x ananassa)

22. RHIZOME
 Rhizomes are modified underground stems
that give rise new plants.E .g Ginger

23. SUCKER
 Suckers are modified underground stems
that give rise new plants.E g Chrysanthemum

24. Tubers
Tubers are underground food
stores which stores food over
the winter and provides a new
plant with food until it can
make its own.
Food made by the new plant is
sent to make new tubers.
Thereby reproducing itself.
Examples: potato,
artichoke, yam, cassava,
water chestnut, arrowroot
Taro-
Japanese
potato

25. Bulbs
 Bulbils are fleshy buds which take part in
vegetative propagation. E.g. daffodils, lilies

26. OFFSET
 The ‘terror of Bengal’ this is nothing but the
aquatic plant ‘water hyacinth’ which is one of
the most invasive weeds found growing
wherever there is standing water. It drains
oxygen from the water, which leads to death of
fishes.
 It reproduce through offset.

28. Artificial Propagation
 2 methods used to cultivate plants asexually
-taking cuttings
-grafting

29. Cutting
They can be placed in moist
soil or water (and sometimes
dipped in rooting
powder).
Cuttings are small pieces of stem with some leaves
attached, the new plant grows from this.

30. Grafting
A cut stem of one plant (with good flower or fruit
growth) (the graft) is taken and firmly attached
to the rootstock of another plant (which has a
strong, established root system) (the stock).
Examples- roses, fruit trees

31. Commercial aspects
Artificial propagation has allowed us to
adapt and improve plants for our own
use.
Some of the benefits include:
•Quick production of large numbers of
genetically identical plants.
•Specific varieties, desired features or
consistent quality can be produced
especially in fruit, flowers.

32. Parthenogenesis(Virgin birth)
 In some organisms like rotifers, honeybees
and even some lizards and birds (turkey), the
female gamete undergoes development to
form new organisms without fertilisation.
 This phenomenon is called parthenogenesis.

33. Parthenogenesis
 Offspring can arise from
unfertilized eggs.
 Includes some Fish,
Reptiles, Amphibians and
Aphids.
 Most of these species can
switch between Sexual
and Asexual Reproduction.
(depending on conditions)

37. Asexual Reproduction
 Asexual reproduction is natural “cloning.”
Parts of the plant, such as leaves or stems,
produce roots and become an independent
plant.
 List some benefits and some drawbacks to
asexual reproduction.
 To overcome the demerits of asexual
reproduction plants and animal exhibits
sexual reproduction.

38. REPRODUCTION IN
ORGANISMS
Sexual reproduction

39. Sexual Reproduction
 Sexual reproduction requires fusion of male
cells in the pollen grain with female cells in
the ovule.
 List some advantages and drawbacks to
sexual reproduction.

40. SEXUAL REPRODUCTION
 Sexual reproduction involves formation of the
male and female gametes, either by the same
individual or by different individuals of the
opposite sex.
 These gametes fuse to form the zygote which
develops to form the new organism.

41. STAGES IN LIFE
 Plants–the annual and biennial types, show
clear cut
 1.Vegetative phase,
 2.Reproductive phase and
 3.Senescence phase, .
 In animals, the juvenile phase is followed by
morphological and physiological changes prior
to active reproductive behaviour.
 The reproductive phase is also of variable
duration in different organisms.

42. JUVENILE STAGE
 All organisms have to reach a certain stage of
growth and maturity in their life, before they
can reproduce sexually.
 That period of growth is called the juvenile
phase. It is known as vegetative phase in
plants.
 This phase is of variable durations in different
organisms.

43. REPRODUCTIVE PHASE
 All organisms have to reach a reproductive
maturity in their life called reproductive stage.
 Among animals, for example birds, do they lay
eggs all through the year? Or is it a seasonal
phenomenon?
 What about other animals like frogs and
lizards?

44. REPRODUCTIVE PHASE
 Birds living in nature lay eggs only seasonally.
 However, birds in captivity (as in poultry farms)
can be made to lay eggs throughout the year.
 The females of placental mammals exhibit
cyclical changes in the activities of ovaries and
accessory ducts as well as hormones during
the reproductive phase.

45. REPRODUCTIVE PHASE
 In non-primate mammals like cows, sheep,
rats, deers, dogs, tiger, etc., such cyclical
changes during reproduction are called
oestrus cycle or heat cycle.
 In primates (monkeys, apes, and humans)
there is periodic blood flow from uterus it is
called menstrual cycle.

46. REPRODUCTIVE PHASE
 Many mammals, especially those living in
natural, wild conditions exhibit menstrual
cycles only during favourable seasons in their
reproductive phase and are called seasonal
breeders.
 Many other mammals are reproductively
active throughout their reproductive phase and
hence are called continuous breeders.

47. SENESCENCE STAGE
 All organisms reach to a reproductive
maturity and then growing older in their
life called senescence stage.
 This phase can be considered as one of
the parameters of senescence or old age.
 There are concomitant changes in the
body (like slowing of metabolism, etc.)
during this last phase of life span. Old age
ultimately leads to death.

48. Events in sexual
reproduction
 After attainment of maturity, all sexually
reproducing organisms exhibit events and
processes that have remarkable
fundamental similarity, even though the
structures associated with sexual
reproduction are indeed very different.
 Sexual reproduction is characterised by
the fusion (or fertilisation) of the male and
female gametes, the formation of zygote
and embryogenesis.

49. Events in sexual
reproduction
 For convenience these sequential events may
be grouped into three distinct stages namely,
 1.Pre-fertilisation,
 2.Fertilisation and
 3. Post-fertilisation events.

50. 1.Pre-fertilisation
 These include all the events of sexual
reproduction prior to the fusion of gametes.
 The two main pre-fertilisation events are
 (A) Gametogenesis and
 (B) Gamete transfer.

51. (A) Gametogenesis
 Gametogenesis refers to the process of
formation of the two types of gametes –
male and female.
 Gametes are haploid cells.
 In some algae the two gametes are so
similar in appearance that it is not
possible to categorise them into male and
female gametes.
 They are hence called homogametes
(isogametes)

52. Cont.
 In a majority of sexually reproducing
organisms the gametes produced are of two
morphologically distinct types
(heterogametes).
 In such organisms the male gamete is called
the antherozoid or sperm and the female
gamete is called the egg or ovum.

53. Gametogenesis: Male

54. Gametogenesis: Female

55. (B) Gamete transfer.
 Male and female gametes must be physically
brought together to facilitate fusion
(fertilisation).
 There is a need for a medium through which
the male gametes move. In several simple
plants like algae, bryophytes and
pteridophytes, water is the medium through
which this gamete transfer takes place..

56. POLLINATION
 In seed plants, pollen grains are the carriers of
male gametes and ovule have the egg.
 Pollen grains produced in anthers therefore,
have to be transferred to the stigma before it
can lead to fertilisation.
 A specialised event called pollination facilitates
transfer of pollen grains to the stigma.

57. 2.Fertilisation
 The most vital event of sexual
reproduction is perhaps the fusion of
gametes. This process called syngamy
results in the formation of a diploid
zygote.
 The term fertilisation is also often used for
this process.
 It is of two types-
 External fertilization and
 Internal fertilization

58. 3. Post-fertilisation events
 Events in sexual reproduction after the
formation of zygote are called post-fertilisation
events.
 It includes
 Zygote and
 Embryogenesis

59. The Zygote
 Formation of the diploid zygote is universal in
all sexually reproducing organisms.
 In organisms with external fertilisation, zygote
is formed in the external medium (usually
water), whereas in those exhibiting internal
fertilisation, zygote is formed inside the body of
the organism.

60. Embryogenesis
 Embryogenesis refers to the process of
development of embryo from the zygote.
 Zygote undergoes cell division (mitosis) and
cell differentiation.
 While cell divisions increase the number of
cells in the developing embryo; cell
differentiation helps groups of cells to undergo
certain modifications to form specialised
tissues and organs to form an organism.

61. Cont.
 In flowering plants, the zygote is formed inside
the ovule.
 After fertilisation the sepals, petals and
stamens of the flower wither and fall off.
 The zygote develops into the embryo and the
ovules develop into the seed. The ovary
develops into the fruit which develops a thick
wall called pericarp that is protective in
function.

62. Seed Germination

63. END OF CHAPTER