Reproduction in Organism || Biology || Class 12 ||

2. • The period of birth to natural death of an organism is called life span.
No individual is immortal except unicellular organism. Because it
continue its life in progeny by fission.
INTRODUCTION:
Reproduction
It is a biological process in which an organism gives rise to young ones
or offspring.
Reproduction enables the continuity of species generation after
generation.
Reproduction is important because the continuity of life on earth is
achieved by the process of reproduction.
CHAPTER 01 - REPRODUCTION IN ORGANISM

3. Sexual Asexual
Two parents (a male and a
female)
A single parent is involved
Formation and fusion of
gametes
No formation or fusion of
Gametes
Involves meiosis Involves mitotic division
Individuals show variation i.e.
Offspring
Individuals are genetically
identical i.e. clone
TYPES OF REPRODUCTION
CHAPTER 01 - REPRODUCTION IN ORGANISM

4. MODES OF ASEXUAL REPRODUCTION
1. Binary fission:
The single cell organism of kingdom Monera and Protista reproduce by
simple cell division called binary fission. The cell divides in to two half. Each
half develops in to new adult.
2. Spore Formation:
A. Zoospores - These are motile asexual spores of algae, fungi. They use
flagellum for locomotion.
CHAPTER 01 - REPRODUCTION IN ORGANISM

5. B. Conidia - These are the asexual
spores of fungus generated by mitosis.
Ex: penicillium
3. Budding :
In some organism cell division is
unequal and small buds are
produced. Initially these are
attached to parent cells. Later
separates and develops into new
individual.
Ex. Hydra, Yeast
CHAPTER 01 - REPRODUCTION IN ORGANISM

6. Gemmules: These are the internal buds of fresh water sponges. They
resist drought, high temp, freezing, lac of oxygen etc.
4. Vegetative Reproduction :
It is the form of reproduction in which new plant grows from a
fragment of the parent plant or a specialized reproductive structures.
CHAPTER 01 - REPRODUCTION IN ORGANISM

7. VEGETATIVE PROPAGULES
1. Runner or stolon:
It is slender stem that grows horizontally to ground.
Naturally it cut off and separated develops in to new individual.
Ex: strawberry.
2. Rhizome:
It is the modified underground stem. If a rhizome is separated into pieces, each
piece may be able to give rise
to a new plant.
Ex: Ginger. Canna
3. Suckers:
It is a basal shoot, root sprout, adventitious shoot. It grows from a bud at the
base of a tree or shrub or from its roots.
Ex: Cherry. Apple.
CHAPTER 01 - REPRODUCTION IN ORGANISM

8. 4. Tuber:
Tubers are modified plant structures that are enlarged to store nutrients.
• These are short, thickened underground stem.
• It bears minute scale leaves with a bud. It has the ability for developing into a
new plant.
Ex: potato
5. Offset:
Offset is a small, virtually complete daughter plant that asexually produced on
the mother plant.
Ex: water hyacinth.
6. Bulb:
A bulb is a short stem with fleshy leaves or leaf bases.
Ex: Onion, Garlic
CHAPTER 01 - REPRODUCTION IN ORGANISM

9. SEXUAL REPRODUCTION
Events
Pre- Fertilisation
Gametogenesis Gamete transfer
Fertilisation /
Syngamy
Post- Fertilisation
Zygote formation
And
Embryogenesis
CHAPTER 01 - REPRODUCTION IN ORGANISM

10. It involves the formation of male and female gametes in same individual
( bisexual) or different individual (unisexual) of opposite sex.
• All organism reaches the stage of growth and maturity before they
reproduce sexually.
PRE-FERTILISATION CHANGES
(a)Gametogenesis
• It is the process of formation of haploid male and female gametes.
• Gametes may be homogametes (isogametes) or heterogametes.
• In heterogametes the male gamete is called antherozoid or sperm
and the female gamete is called the ovum.
• If the parent body is haploid gametes are formed by mitosis, if
diploid gametes are formed by meiosis.
• An organism may be homothallic/monoecious or
heterothallic/dioecious.
CHAPTER 01 - REPRODUCTION IN ORGANISM

11. (b) gamete transfer
• Fusion of male and female gamete is called fertilisation.
• So male and female gamete must be brought together.
• In some organisms both gametes are motile (algae) but in most
cases male gamete is motile where as female is not.
• Algae, bryophytes and pteridophytes, water is the medium for
gamete transfer.
• Pollination is the method of gamete transfer in higher plants as
pollen grains contain male gametes.
• The number of male gametes are thousand times the number
of female gametes as there is loss of male gametes during
transfer.
• In dioecious animals there is special mechanism for gamete
transfer.
CHAPTER 01 - REPRODUCTION IN ORGANISM

12. SYNGAMY AND FERTILISATION
• It results in the formation of diploid zygote.
• In some animals like rotifers, honey bees, some lizards and
birds (turkey) female gametes develop into organism without
fertilisation, such a phenomenon is called parthenogenesis.
POST-FERTILISATION EVENTS
• The events after zygote formation is called postfertilisation
events.
• Zygote development (i) type of life cycle of organism and (ii)
the environment it is exposed to.
• In algae and fungi it develops a thick wall around it to resist
desiccations and damage and undergoes a period of rest.
• Organisms showing haplontic life cycle, zygote undergoes
meiosis. While organisms showing diplontic life-cycle
undergoes mitosis. CHAPTER 01 - REPRODUCTION IN ORGANISM

13. • The zygote develops into an embryo.
• Embryogenesis involves (i) cell division (ii) cell enlargement
or growth (iii) cell differentiation.
• In oviparous animals zygote development occurs outside of
female’s body, they are egg laying e.g. reptiles, birds.
• In viviparous animals zygote development occurs inside of
female’s body. They give birth to young individuals. E.g.
mammals
• In plants zygote is formed inside ovule, where it develops into
embryo, then ovule becomes seed and ovary into fruit.
• Germination of seeds produce new plants.
CHAPTER 01 - REPRODUCTION IN ORGANISM

14. TYPES OF FERTILISATION
EXTERNAL
FERTILISATION
INTERNAL
FERTILISATION
Syngamy occurs outside of the
body of organisms.
Syngamy occurs inside of the
body of organisms.
Large number of gamets (male
& female) are released into
surrounding medium. E.g.
bony fish, amphibian
Number of ova are less, but
large number of male gametes
are formed. E.g. birds,
mammals, earthworm
CHAPTER 01 - REPRODUCTION IN ORGANISM

15. SOME USEFUL TERMS -
• Clone : Morphologically and genetically similar individuals.
• Juvenile Phase : It is the period of growth and maturity before an
organism can reproduce sexually.
• Meiocytes : These are specialized cells of diploid organisms which
undergo meiosis to produce gametes.
• Pericarp : It is the protective coverning of fruit, may be divided into
epicarp, mesocarp and endocarp.
• Parthenogenesis : Development of an egg into an embryo without
fertilisation. e.g. in rotifers, honeybees, turkey and some lizards.
• Monoecious Plants : Plants having both male and female ¯owers on
same plant. e.g. cucurbits and coconut. The term ‘homothallic’is used in
Fungi for same condition.
CHAPTER 01 - REPRODUCTION IN ORGANISM

16. • Dioecious Plants : Plants having male and female flowers on separate plant.
e.g. Papaya and date palm. The term ‘heterothallic’ is used in fungi for the
same condition.
• Oestrus Cycle : The reproductive cycle in non-primate mammals like cows,
sheep, rats, deer, dogs and tigers etc;. The sexually active females reffered to
as being in ‘heat’ at a specific time of Oestrus cycle. They reabsorbs the
endometrium if conception does not occur
CHAPTER 01 - REPRODUCTION IN ORGANISM

17. • THANK YOU •