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BIOLOGY REPRODUCTION IN ORGANISMS

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Asexual Reproduction

Lifespan

The period from birth to the natural death of an organism is called its lifespan.

It includes four stages—juvenility, maturity, ageing and senescence or death.

Reproduction

Reproduction is defined as a biological process in which an organism gives rise to an offspring similar

to itself.

Types of Reproduction

Asexual reproduction: The process by which offspring is produced by a single parent with or without

the formation of gametes is called asexual reproduction.

Sexual reproduction: The process by which offspring is produced by two parents of the opposite sex,

which involves the fusion of male and female gametes is called sexual reproduction.

Characteristics of Asexual Reproduction

A single parent is involved.

Gametes are not formed.

Fertilisation does not take place.

Involves only mitotic cell division.

Offspring are genetically identical to the parent.

Rapid multiplication.

The lifespan of some microorganisms ranges from few minutes to

few hours, while that of Sequoia (Red wood tree) is 3000–4000

years.

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Types of Asexual Reproduction

Fission

Fission is the division of the parent body into two or more daughter individuals identical to the parent

organism.

It can take place through binary fission, multiple fission and plasmotomy.

Asexual Reproduction

Fission

Binary Fission

Simple Binary Fission

Longitudinal Binary Fission

Transverse Binary Fission Multiple Fission

Plasmotomy Budding

Fragmentation

Gemmae formation

Regeneration

Morphallaxis

Epimorphosis

Sporulation

Vegetative Propagation

Natural Vegetative Propagation

Artificial Vegetative Propagation

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Binary Fission

In binary fission, the parent organism divides mitotically into two halves, each half forming an

independent daughter individual.

The offspring produced are genetically identical to the parent and one another.

Depending on the plane of division, binary fission is of the following types:

i. Simple Binary Fission: Division occurs through any plane. Example: Amoeba

ii. Longitudinal Binary Fission: The plane of division passes along the longitudinal axis of the

organism. Example: Euglena

iii. Transverse Binary Fission: The plane of division runs along the transverse axis of the organism.

Examples: Paramoecium, Planaria

In binary fission, the parent body as a whole constitutes the reproductive unit and

disappears when its division into daughter individuals is completed. So, the parent cannot

be said to have died as no dead body is left. After binary fission, the parent continues

living as two daughter individuals. Thus, organisms which undergo binary fission are said

to be immortal.

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Multiple Fission

In multiple fission, the parent body divides into many similar daughter individuals.

It produces several daughter cells from a single parent cell at the same time.

Multiple fission occurs in protozoa such as Amoeba (sporulation) and malarial parasite such as

Plasmodium (schizogony).

Plasmotomy

Plasmotomy involves the division of a multinucleate parent into several multinucleate daughter

individuals without the division of nuclei.

The division of nuclei occurs later on to maintain a constant number of nuclei.

Plasmotomy occurs in protozoans such as Opalina and Pelomyxa.

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Budding

In budding, one or more small protuberances called buds develop from a single parent body.

Each bud then separates from the parental body and assumes an independent existence.

Budding is seen in sponges such as Scypha, coelenterates such as Hydra, annelids such as Syllis and

tunicates such as Salpa.

Budding in animals is of the following types:

i. Exogenous/External Budding: In exogenous budding, the bud grows externally on the surface of

the body. Examples: Sycon, Hydra

ii. Endogenous/Internal Budding: In endogenous budding, buds are formed within the parent’s

body. Examples: Spongilla, few marine sponges

iii. Strobilation: The process of repeated formation of similar segments by budding is called

strobilation. Examples: Aurelia, Taenia

Fragmentation

In fragmentation, the parent body breaks up into several parts called fragments.

Each fragment then develops into a complete organism.

Fragmentation is observed in sponges, coelenterates such as sea anemones, echinoderms, algae

such as Spirogyra, fungi such as Rhizopus, bryophytes such as Riccia and pteridophytes such

as Selaginella.

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Regeneration

Regeneration is the ability of organisms to generate lost or damaged parts.

In some animals, the entire organism is regenerated, while in others, only a part of the organism

is regenerated.

Regeneration is of the following types:

i. Morphallaxis: In morphallaxis, the entire body grows from a small fragment. Examples: Sponges,

Hydra, Planaria

ii. Epimorphosis: Epimorphosis is the replacement of lost parts of the body. It is of the

following types:

a. Reparative Regeneration: Only some damaged tissues can be regenerated.

b. Restorative Regeneration: Several parts of the body can be regenerated.

Gemmae Formation

Gemmae are propagules which detach from the parent body and grow into new individuals.

Reproduction through gemmae is observed in Marchantia.

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Sporulation

During sporulation, the parent plant or sporophyte produces hundreds of reproductive units called

spores inside the sporangia.

When the spore case ruptures or bursts, the spores spread into the air.

When the air-borne spores land on food, soil or any suitable substratum under favourable conditions,

they germinate and give rise to new organisms with many vegetative hyphae.

Sporulation is observed in Rhizopus, Mucor and Aspergillus.

Types of Spores

Spores

Motile spores

Zoospores (Ulothrix)

Non-motile spores

Conidia (Penicillium)

Chlamydospores (Rhizopus)

Oidia (Agaricus)

Sporangiospores (Mucor)

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Vegetative Propagation

In vegetative reproduction, new plants are produced from the vegetative parts of plants.

The newly formed individuals are genetically identical to the parent plant.

Vegetative reproduction is a common method of reproduction in flowering plants.

There are two types of vegetative reproduction:

i. Natural vegetative reproduction

ii. Artificial vegetative reproduction

Natural Methods of Vegetative Reproduction

In natural vegetative propagation, a somatic part of the plant detaches from the body of the mother

plant and develops into a new independent plant under suitable environmental conditions.

The detachable somatic part which functions in vegetative propagation is called a

vegetative propagule.

Natural Vegetative Reproduction

Roots Underground

stem

Tubers

Bulbs

Corms

Rhizomes

Suckers

Subaerial/ Creeping

stem

Runners

Stolons

Offsets

Aerial stems Leaves Bulbils Turions

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Propagation by Roots

Tap roots, fleshy roots and adventitious roots take part in vegetative propagation.

Tap roots of some plants develop adventitious buds to form new plants

Propagation by roots takes place in guava, poplar, sweet potato, Dahlia and Asparagus.

Propagation by Underground Stems

Different types of underground stem structures can take part in vegetative propagation.

i. Tubers: Examples: Artichoke, potato

ii. Bulbs: Examples: Garlic, onion

iii. Corms: Examples: Colocasia, Crocus

iv. Rhizomes: Examples: Ginger, turmeric

v. Suckers: Examples: Mint, Chrysanthemum

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Propagation by Subaerial/Creeping Stems

Creeping stems are of three types—runners, stolons and offsets.

i. Runners: Examples: Cynodon, Oxalis

ii. Stolons: Examples: Strawberry, Vallisneria

iii. Offsets: Examples: Eichhornia, Pistia

Propagation by Aerial Stems

Each segment of a fleshy phylloclade can give rise to a new plant.

Propagation by aerial stems takes place in Opuntia and sugarcane.

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Propagation by Leaves

Adventitious buds present on the leaves of several plants help in vegetative propagation.

Propagation by leaves takes place in Begonia and Bryophyllum.

Propagation by Bulbils

Bulbils are multicellular fleshy buds which give rise to new plants.

Propagation by bulbils takes place in Oxalis, Agave and pineapple.

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Propagation by Turions

Turions are fleshy buds in aquatic plants which help in perennation.

They get detached from the parent plant and remain inactive through the winter and give rise to a new

plant in the following spring.

Propagation by turions takes place in Utricularia and Potamogeton.

Artificial Methods of Vegetative Reproduction

In the artificial method of vegetative propagation, a part of the somatic body of a plant is made to

develop into new independent plants.

Artificial methods help to propagate plants of desired varieties.

Artificial Vegetative Reproduction

Cuttings

Stem Cuttings

Leaf Cuttings

Root Cuttings

Layering

Tip Layering

Trench Layering

Serpentine Layering

Mound Layering

Air Layering

Grafting

Tongue Grafting

Wedge Grafting

Crown Grafting

Approach Grafting

Bud Grafting

Micropropagation

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Cuttings

Cuttings are cut pieces of roots, stems and leaves which are planted in nurseries.

In cutting, a portion of the stem, leaf or root is removed and fixed into the soil to allow the growth of

roots and shoots.

Root-promoting chemicals such as indole butyric acid (IBA) and naphthalene acetic acid (NAA) are

used for propagation through cuttings.

Propagation through cuttings takes place in the following ways:

i. Root cuttings: Examples: Lemon, orange

ii. Stem cuttings: Examples: Rose, sugarcane

iii. Leaf cuttings: Examples: Snake plant, Saintpaulia

Layering

Layering is a method in which adventitious roots are induced to develop on a soft stem while it is still

attached to the plant.

In layering, a branch of the plant is covered with some material and supplied with water to

produce roots.

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Propagation through layering takes place in the following ways:

i. Tip layering: Examples: Blackberry, raspberry

ii. Trench layering: Examples: Walnut, mulberry

iii. Serpentine layering: Example: Clematis

iv. Mound layering: Examples: Apple, pear

v. Air layering: Examples: Litchi, pomegranate

Grafting

Grafting is a technique of joining two parts, usually a root system and a shoot system of two different

plants in such a way that they unite and later develop as a composite plant.

Propagation through grafting occurs in mango, apple, pear, peach and pine.

Grafting can be carried out in the following ways:

i. Tongue grafting

ii. Crown grafting

iii. Wedge grafting

iv. Side grafting

v. Approach grafting

vi. Bud grafting

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Micropropagation

Micropropagation is the technique of production of new plants from cells or tiny pieces of plant tissues

which are removed from the growing tips of a plant and put into a suitable growth medium called the

culture solution to produce a callus, which gets differentiated into a plantlet.

Micropropagation is used for the commercial production of orchids, carnation, Gladiolus,

Chrysanthemum and other ornamental plants.

Advantages and Disadvantages of Vegetative Propagation

Advantages

•Only method of multiplication in seedless plants

•Multiplication of plants without any change or variation

•Rapid multiplication

•Genetic uniformity

•Production of disease-free plants

•Almost 100% survival rate of plants

•Good plant qualities can be preserved for a long time

•Production of transgenic plants

Disadvantages

•Vegetative propagules are prone to viral, bacterial and fungal diseases

•Propagules can get easily decayed

•No chances of variation

•No dispersal of propagules which may cause overcrowding

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Advantages and Disadvantages of Asexual Reproduction

Advantages Disadvantages

1. Uniparental reproduction. 1. Mixing of genetic material does not

take place, and so, there is no

variation.

2. Involves simple processes such as

division and mitosis.

2. In the absence of variation,

evolution does not take place.

3. Quick mode of reproduction. 3. Rapid multiplication causes

overcrowding.

4. A single parent may produce a large

number of offspring.

4. Organisms produced through

asexual reproduction have low

adaptability to the changed

environment.

5. Young ones are genetically similar to

their parent.