Reproduction in Organisms
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Concept Tutorials
Life Span
 Period from birth to natural death of an organism is called life span.
 There is no co- relation between life span and size of organism.
 For example: Crow and parrot are not very different in body size yet
their life span show a wide difference crow- 15 years and parrot- 140
years. Lifespan of much larger crocodile is about 60 years while that of
tortoise is 100 years.
 No individual is immortal except unicellular organisms.
 No residue of parental cell is left behind after reproduction and living
content of parental cell perpetuates in daughter cells. Therefore,
unicellular organisms are considered as immortal.
 Natural death does not occur in unicellular organisms.
Reproduction
Reproduction is the biological
process in which an organism give
rise to offspring of its own kind. It
enables continuity of species.
Reproduction is not essential for
survival of individual but it is
required for continuation of
species.
Asexual Reproduction
 Single parent is involved.
 No formation and fusion of gametes.
 Only mitotic division occurs during reproduction.
 Progeny is genetically similar to parent as mitotic division produces
no variations. So asexual reproduction does not play important role
in evolution.
 Identical offsprings resulting from single parent are called clone.
 Mutation is the only means of introducing variation in the species.
 In unicellular organisms, cell division is itself a mode of
reproduction.
Binary Fission occurs in unicellular organisms like Amoeba during favorable
conditions. Multiple Fission occurs in Amoeba during unfavorable conditions.
Plasmodium (malarial parasite) reproduces by multiple fission called
schizogony.
 Under unfavorable condition, Amoeba
withdraws its pseudopodia and
secretes thick cyst around itself. This
phenomenon is called Encystation.
 When favorable conditions return
encysted amoeba undergoes multiple
fission and produces many minute
amoebae (pseudopodiospores).
 The cyst wall burst and spores are
liberated in surrounding to grow up
into
many
amoebae.
This
phenomenon
is
known
as
sporulation.
Zoospore
Zygote
Asexual reproduction
Sexual reproduction
Flagellated and motile
Non-flagellated and nonmotile
Formed inside sporangium Formed by fusion of two
gametes
Haploid or diploid
Always diploid
Gemmules
 Gemmules
are formed by freshwater
sponges during unfavorable conditions.
 Archeocytes (totipotent cells) present in
gemmules (internal buds) of sponges are
totipotent i.e. these are capable of giving rise
to whole organism on arrival of favorable
condition.
Fragmentation
 Fragmentation is defined as the process of breaking up of parent animal
into small parts, each of which can grow into a new complete individual.
 This process of asexual reproduction is found in Planaria, Spirogyra and
hydra.
Vegetative Propagation In Plants
Vegetative parts of plant which are capable of
giving rise to new offspring are called
vegetative propagules and such mode of
reproduction is called vegetative propagation.
Plants like potato, ginger, sugarcane, banana
etc. have ability to give rise to adventitious
buds from nodes when come in contact of
damp soil or water.
This ability is fully exploited by gardeners
and farmers for commercial propagation of
such plants.
Vegetative Propagation In Plants…Runners

Runners
exhibit
horizontal
growth at or just below the soil
surface.

As runners grow, they develop
roots and shoots from buds
located at nodes.

New plants arise at nodes where
roots and shoots develop.

This type of propagation is seen in
strawberry plants and grass.
Vegetative Propagation In Plants…
Adventitious buds develop from places other
than a leaf axil.
Roots which develop from various parts of plants
other than radical are called adventitious roots.
Vegetative Propagation In Plants…
Water Hyacinth
 It was introduced in Bengal in India
because of its beautiful flowers and
shapes of leaves, but turned out to be
an invasive weed draining oxygen from
the water bodies and resulted in death
of many fishes.
 Fish is a supplement food in Bengal,
and because of the fish scarcity in
Bengal caused by Eichhornia, the water
hyacinth is also called "Terror of
Bengal".
Important Note
During unfavorable condition, asexually reproducing organisms shift
to sexual reproduction because sexual reproduction introduces
variations which increase chances of survival.
Sexual Reproduction
 Bi-parental reproduction.
 Haploid gametes are formed which fuse to form diploid zygote.
 Zygote is the first cell of new individual.
 Meiosis occurs during gametogenesis while mitosis occurs
during embryogenesis.
 Offspring are genetically different from parents as variations
occur during crossing over in meiosis. So sexual reproduction
plays important role in evolution.
 It has biological advantages of promoting genetic variety, hence
better adaptation.
 Rate of reproduction is slow.
Important Note
In
both plants and animals, hormones are responsible for
transitions between three phases.
Interaction
between hormones and environmental factors
regulates reproductive processes in organisms.
Important Note
Bamboo species flower once in their
lifetime (50- 100 years), produce large
number of fruits and die.
Strobilanthes kunthiana (neelakuranji)
flowers once in 12 years. It flowered in
2006. Its mass flowering transformed
large tracks of hilly areas in Kerala,
Karnataka and Tamil Nadu into blue
stretches and attracted a large number of
tourists.
Primates
Reproductive Cycle
 Cyclic changes in the activities of
ovaries and accessory ducts as well
as hormones during the reproductive
phase is called reproductive cycle.
 In non-primate mammals like cows,
sheep, rats, deer, dogs, tiger, etc. such
cyclic changes during reproduction
are called estrus cycle whereas in
primates (monkey, apes and humans)
it is called menstrual cycle.
Menstrual Cycle
It occurs in primates
only.
For
example:
Human.
Menstruation occurs in
this cycle.
Female is continuous
breeders.
Estrus Cycle
It occurs in nonprimates. For example:
Dog and cat.
Menstruation does not
occur.
Female
is
seasonal
breeder.
Gametogenesis
 Formation of gametes is called
gametogenesis.
 Male
gamete
is
antherozoid or sperm.
called
 Female gamete is called ovum or
egg.
 In diploid organisms, specialised
cells called meiocytes (gamete
mother cell) undergo meiosis to
form gametes.
Anisogamy
Oogamy
Unisexual
Bisexual
Heterothallic
Homothallic
Marchantia
Papaya
Date palm
Chara
Cucurbits and coconuts
Papaya and date palm
Types of Flowers
Gamete Transfer in Plants
 In majority of organisms, male gametes are motile and female gametes
are non- motile except in fungi and algae in which both gametes are
motile.
 In simple plants like algae, fungi, bryophytes and pteridophytes, water
is the medium through which gametes move.
 The number of male gametes are much more than the number of
female gametes as most of the male gamete fail to reach female gamete.
 In higher plants, pollen grains are carrier of male gametes and
ovules contains eggs.
 Transfer of pollen grain from anther to stigma is called pollination.
Because of proper embryonic care and protection, the chances
of survival of young one is greater in viviparous organisms as
compared to oviparous organisms.
Fertilization
 Organisms having external fertilization show great synchrony
between the sexes and release a large number of gametes into the
surrounding medium in order to enhance the chances of syngamy.
 A major disadvantage of external fertilization is that the offsprings
are extremely vulnerable to predators threatening their survival up
to adulthood.
 In case of internal fertilization, the male gamete is motile and has to
reach the egg. Therefore, number of sperms produced is still very
large but there is a significant reduction in the number of eggs
produced.
 Note: Internal fertilization greatly enhances chances of syngamy.
Parthenogenesis
In some organisms like honeybees (drone- male honeybee), some
lizards and birds (turkey), egg undergoes development to form new
organism without fertilization. This phenomenon is called
parthenogenesis.
Post Fertilization Events
 Zygote is the end-product of syngamy and is the first cell of future
individual. It is considered as the vital link that ensures continuity of
species from one generation to next.
 Embryogenesis is the process by which the embryo forms and
develops. Zygote undergoes repetitive cell division and differentiation to
give rise to complete individual. During cell differentiation, certain
modification occurs in group of cells to form specialized tissues and
organs.