CH A P TER

01
Reproduction in Organisms |1

RËPRØDÜÇTÏØÑ ÏÑ
ØRGÅÑÏSMS
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Reproduction is a process in which an organism produces

1 young ones (offspring) similar to itself.

The period from birth to the natural death of an organism

is known as its lifespan. 2

No individual is immortal, except unicellular (single

3 celled) organisms. There is no natural death in unicellular
organisms.

Life Spans of Some Organisms

Organism Lifespan Organism Lifespan

Rose 5-7 years Parrot 140 yrs
Rice Plant 3-7 months Crocodile 60 yrs
Banyan tree 200+ yrs Horse 35-50 yrs
Banana tree 25 yrs Tortoise 100-150 yrs
Dog 20 yrs Crow 15 yrs
Butterfly 1-2 weeks Cow 25 yrs
Fruit fly 2 weeks Elephant 60-70 yrs
Based on the number of participants, reproduction is of 2 types:
 Asexual reproduction & Sexual reproduction.

ÅSËXÜÅL RËPRØDÜÇTÏØÑ

It is seen in
It is the unicellular
production of organisms,
offspring by a simple plants &
single parent. animals.

The offspring Such

morphologically
are identical
and genetically
to one another similar individuals
and to their are known as
parent. clone.
Reproduction in Organisms |3

 Fission: In this, the parent cell divides (cell division) into two or more
individuals. E.g. Protists and Monerans.
Fission is of 2 types:

A Binary fission: Parent cell divides into 2 halves and each

rapidly grows into adults. Amoeba, Paramecium.

B Multiple fission: It is the division of parent cell into many

individuals. E.g. Plasmodium, Amoeba.

 Under unfavourable conditions, the Amoeba withdraws its pseudopodia

and secreates a three layered hard covering or cyst around itself. This
process is known as encystation.
 When favourable conditions return, the encysted Amoeba divides by
multiple fission and produce pseudopodiospores (many minute
Amoeba). The cyst wall burst out and spores are liberated into the
surrounding medium (sporulation).
Bud
 Budding: In this, a bud is
produced that remain attached
initially to the parent cell. After
maturation, it is detached
from parent body to form new
individual. E.g. Hydra, Sponge,
Yeast, etc. Parent cell
 Vegetative propagation: It is the Budding in Yeast
production of offspring from vegetative propagules in plants. Vegetative
propagules are units of vegetative propagation.
Examples for vegetative propagules:
lenticels
scale leaf
lateral bud Nodes
(eye) shoot Buds
stem end

Adventitious root
(a) (b)

(a) Buds (eyes) of the (b) Rhizomes of banana &

potato tuber (AIPMT 2011) ginger (AIPMT 2015)
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Adventitious
Buds

(c) (d) (e)

(c) Bulbil of Agave (MAINS (d) Leaf buds of

2011 Cancelled) Bryophyllum

(e) Offset of water (f) Runner, sucker, bulb

hyacinth etc.

 Eichhornia crassipes: It is one of the most invasive weeds found in

standing water and also known as ‘Terror of Bengal’. It propagates at
phenomenal rate (difficult to get rid off) and spread over the water
body draining oxygen from water, which leads to death of fishes. It was
introduced in India because of its beautiful flowers and shape of leaves.

01
Buds & rhizomes arise from the nodes of modified
stems. The nodes come in contact with damp soil or
water and produce roots and new plants.

Adventitious buds of Bryophyllum. They arise from the

notches at margins of leaves. 02
 Other asexual reproductive structures: E.g. Zoospores (microscopic
motile structures in some algae and fungi), conidia (Penicillium) and
gemmules (sponge). (AIPMT 2015)
 Fragmentation: Body of an organism breaks into distinct pieces
(fragments), each fragment grows into an adult. Eg. Planaria, Spirogyra,
Hydra, etc.
Reproduction in Organisms |5

Asexual reproduction is
the common method of Higher plants reproduce
reproduction in simple asexually (vegetative) &
organisms like algae and fungi. sexually. But most of the animals
But during adverse conditions,
show only sexual reproduction.
they can shift to sexual method.

SËXÜÅL RËPRØDÜÇTÏØÑ

1 2 3
It is the reproduction that It results in offspring It is an elaborate,
involves formation of male that are not identical
and female gametes, complex and
either by the same
to the parents or slow process as
individual or by different amongst themselves compared to asexual
individuals of the opposite because of variations. reproduction.
sex. (NEET 2016)

The period of growth to Annual & biennial plants

In higher plants, the
reach maturity before an show clear cut vegetative,
flowering indicates reproductive & senescent
organism can reproduce
sexually is called juvenile the end of vegetative phases. In perennial plants,
phase. In plants it is known phase (beginning of these phases are very
as vegetative phase. reproductive phase). difficult to identify.

4 5 6
Some plants exhibit unusual flowering, e.g.

Bamboo species
flower only once
in their lifetime (after Strobilanthes kunthiana
50-100 years), produce flowers once in 12 years.
large number of fruits
and die. (NEET 2018)
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 In animals, juvenile phase is followed by morphological and physiological

changes prior to active reproductive behavior.
 Birds living in nature lay eggs only seasonally. However, birds in captivity
(e.g. poultry) can be made to lay eggs throughout the year.
 The females of placental mammals exhibit cyclical changes in the
ovaries, accessory ducts and hormones during the reproductive phase.
It is called oestrus cycle in non primates (cows, sheep, rat, deer, dog, tiger,
etc.) and menstrual cycle in primates (monkeys, apes and humans).

BÅSËD ØÑ BRËËDÏÑG SËÅSØÑ, MÅMMÅLS ÅRË ØF 2 TÝPËS:

Seasonal breeders:
The mammals (living Continuous breeders:
in natural conditions) They are reproductively
exhibiting reproductive active throughout their
cycles only during reproductive phase.
favorable seasons.

SËÑËSÇËÑÇË (ØLD ÅGË):

1 2 3
In plants & animals,
During this, hormones cause
It is the last phase of concomitant transition between
lifespan and end of changes occur in the juvenile, reproductive
reproductive phase. body. E.g. Slowing of and senescence
phase. Interaction
metabolism, etc. It between hormones and
ultimately leads to environmental factors
death. regulate the reproductive
processes and the
associated behavioral
expressions of organisms.

ËVËÑTS ÏÑ SËXÜÅL RËPRØDÜÇTÏØÑ

 3 Stages: Pre-fertilisation, Fertilisation & Post-fertilisation events.

PRË-FËRTÏLÏSÅTÏØÑ
 These are the events prior to the fusion of gametes which include
gametogenesis and gamete transfer.
Reproduction in Organisms |7

GÅMËTØGËÑËSÏS

It refers to the process of formation of two types of

01 gametes-male and female. Gametes are haploid
cells.

Homogametes: Similar gametes. They cannot

be categorised into male & female gametes. E.g.
Some algae like Cladophora.
02
Heterogametes: The male and female gametes are

03 of distinct types. Male gamete is called antherozoid

(sperm) and female gamete is called egg (ovum).
E.g. Fucus (an algae), human beings, etc.

BÏSËXÜÅL ÅÑD ÜÑÏSËXÜÅL ØRGÅÑÏSMS

1 Bisexual: Male & female reproductive structures

present in the same individual

2
If male & female flowers are present on same plant,
it is called monoecious. E.g. Cucurbits & coconuts.

3 Bisexual plants: E.g., Hibiscus, Pisum

4
Bisexual animals (hermaphrodites): E.g. Earthworms,
sponge, tapeworm, leech, etc.
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Unisexual: Male and female reproductive structures

5 are present on different individuals. Male and female

flowers are present on different plants, it is called
dioecious. E.g. Papaya & date palm.

In flowering plants, male flower is staminate (bears

stamens) and female flower is pistillate (bears pistils). 6

7
Unisexual animals: Eg. Cockroach, higher animals,
etc. Fungi may be homothallic (bisexual) or
hetrothallic (unisexual).

ÇËLL DÏVÏSÏØÑ DÜRÏÑG GÅMËTË FØRMÅTÏØÑ

 Many monerans, fungi, algae & bryophytes have haploid parental body.
They produce haploid gametes by mitosis. Pteridophytes, gymnosperms,
angiosperms & animals have diploid parental body. They produce
haploid gametes by meiosis of meiocytes (gamete mother cell).

Name of Chromosomes number Chromosome number

organism in meiocytes (2n) in gametes (n)
Human being 46 23
House fly 12 6
Rat 42 21
Dog 78 39
Cat 38 19
Fruit Fly 8 4
Ophioglossum 1260 630
Apple 34 17
Rice 24 12
Maize 20 10
Potato 48 24
Butterfly 380 190
Onion 16 8
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GÅMËTË TRÅÑSFËR
 After the formation of gametes male and female gametes must be
physically brought together to facilitate fusion (fertilisation).
 Male gametes need a medium to move towards female gametes for
fertilization.

In most organisms, male gamete is motile and the female

1 gamete is stationary. In some fungi and algae, both types
of gametes are motile.

In simple plants (algae, bryophytes & pteridophytes), the

2 gamete transfer takes place through water medium. To
compensate the loss of male gametes during transport,
large number of male gametes are produced.

In seed plants, pollen grains (in anthers) carry male

3 gametes and ovule carries the egg. Pollen grains are
transferred to the stigma before fertilisation can take place.

In bisexual self-fertilising plants (e.g. peas), anthers &

4 stigma are closely located, so transfer of pollen grains is
easy.

In cross pollinating plants (including dioecious plants), pollination

helps in transfer of pollen grains to the stigma.

Pollen grains germinate on the stigma and the pollen tubes carrying
the male gametes reach the ovule and discharge male gametes
near the egg.

In dioecious animals, since male and female gametes are formed

in different individuals, successful transfer and coming together of
gametes is critical for fertilisation.

FËRTÏLÏSÅTÏØÑ (SÝÑGÅMÝ)
 It is the fusion of gametes to form a diploid zygote.
 In rotifers, honeybees, some lizards and birds (turkey), the female
gametes undergoes development to form new organisms without
fertilisation. This is called parthenogenesis.
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TÝPËS ØF FËRTÏLÏSÅTÏØÑ
External fertilisation : Syngamy occurs in the external
medium (water), i.e. zygote is formed outside the body of
the organism. Eg. Most aquatic organisms (many algae,
1 bony fishes, etc.) and amphibians. Such organisms show
synchrony between the sexes and release large number of
gametes into the surrounding medium to ensure syngamy.
A major disadvantage is that the offspring are extremely
vulnerable to predators.

Internal fertilisation : Syngamy occurs inside the body of

the organism. E.g. Terrestrial organisms, belonging to fungi,
animals (reptiles, birds, mammals) & plants (bryophytes,
2
pteridophytes, gymnosperms & angiosperms).

In this, non-motile egg is formed inside the female body to where motile
male gamete reaches and fuses. In seed plants, the non-motile male
gametes are carried to female gamete by pollen tubes.
There is large number of sperms produced but the number of eggs is
very low.

PØST-FËRTÏLÏSÅTÏØÑ ËVËÑTS
 Events in sexual reproduction after the formation of zygote.

ZÝGØTË
Sexually reproducing
In organisms with
organisms begin life as

1 2
haplontic life cycle,
a zygote. Development
zygote divides by
of the zygote depends
meiosis into haploid
on the type of life cycle
spores, that grow into
of the organism and the
haploid individuals.
nature of environment.

In fungi and algae, zygote

Zygote is the vital link
develops a thick wall

3 4
that ensures continuity
called zygospore that is
of species between
resistant to desiccation
organisms of one
and damage. It
generation and the
undergoes a period of
next.
rest before germination.
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ËMBRÝØGËÑËSÏS
 It is the development of embryo from the zygote.
 During embryogenesis, zygote undergoes cell division (mitosis) and cell
differentiation.
 Cell divisions increase the number of cells in the embryo. Cell
differentiation helps in the modifications of groups of cells into various
tissues and organs to form an organism.

BÅSËD ØÑ PLÅÇË ØF ZÝGØTË DËVËLØPMËÑT, ÅÑÏMÅLS ÅRË ØF 2 TÝPËS:

OVIPAROUS

Here, animals lay fertilised/unfertilised eggs. E.g.

In reptiles & birds, the fertilised eggs covered by
hard calcareous shell are laid in a safe place. A
After incubation, young ones hatch out.

VIVIPAROUS

Here, the zygote develops into a young one

inside the female body. Later, the young ones are
delivered out of the body. Eg., Most of mammals B
including human beings. Because of proper care
and protection, the chances of survival of young
ones are greater in viviparous organisms.

Notes
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