Biology ASEXUAL REPRODUCTION

KEY TOPICS

`star` General Principle
`star` Reproduction by
A) Cell Division
B) By Special Reproductive Structures
C) By Vegetative Propagation
`star` Significance in real life

GENERAL PRINCIPLE

● In this method, a `color{Violet}"single individual"` (parent) is capable of producing offspring from its `color{Violet}"somatic"` parts.

● As there is single parent involved in the formation of offspring, there is `color{Violet}"no genetic recombination"` to produce even the slight changes in the offspring.

● As a result, the offspring that are produced are not only identical to one another but are also `color{Violet}"exact copies"` of their parent.

● The term clone is used to describe such `color{Violet}"morphologically and genetically"` `color{Violet}"similar individuals"`.

● Asexual reproduction is common among `color{Violet}"single-celled organisms"`, and in plants and animals with relatively `color{Violet}"simple organisations"` and happens by different means.

REPRODUCTION BY A) CELL DIVISION

`color{blue}"Binary fission"`: Binary fission ("division in half") is a kind of `color{violet}"asexual reproduction"` in bacteria and other simple organisms, that involves the `color{violet}"splitting of a parent cell"` into two `color{violet}"equal halves"` after cell division, producing two new independent cells. The genetic material is `color{violet}"replicated"` during this process and also `color{violet}"split equally"` between the two daughter cells.

`color{green} ✍️ color{green} mathbf("KEY CONCEPT")`

● In `color{Violet}"Protists and Monerans"`, the organism or the parent cell divides into two to give rise to new individuals.

● Thus in these organisms cell division is itself a mode of reproduction.

● Many single-celled organisms reproduce by `color{Violet}"binary fission"`, where a cell divides into two halves and each rapidly grows into an adult (e.g., Amoeba, Paramecium).

● In yeast, the division is unequal and `color{Violet}"small buds"` are produced that remain attached initially to the parent cell which, eventually gets separated and mature into new yeast organisms (cells).

B) BY SPECIAL REPRODUCTIVE STRUCTURES

`color{blue}"Zoospores"`: Zoospores are the `color{violet}"motile spores"` which are `color{violet}"thin-walled and flagellated"` and produced for `color{violet}"asexual reproduction"` by some aquatic fungi and algae.

`color{blue}"Conidia"`: Thay are the `color{violet}"asexual, non-motile reproductive spores"` of fungi (kingdom Fungi) usually produced at the `color{violet}"tip or side of hyphae"` (filaments that make up the body of a typical fungus) or on special spore-producing structures called `color{violet}"conidiophores"`. The spores detach when mature.

`color{blue}"Gemmules"`: Gemmules are `color{violet}"internal buds"` found in `color{violet}"adult freshwater sponges"` and are involved in `color{violet}"asexual reproduction"`. It is an asexually reproduced `color{violet}"mass of cells"`, that is capable of developing into a new organism i.e., an adult sponge.

`color{green} ✍️ color{green} mathbf("KEY CONCEPT")`

● Members of the Kingdom Fungi and simple plants such as algae reproduce through special `color{Violet}"asexual reproductive structures"`.

● The most common of these structures are `color{Violet}"zoospores"` that usually are microscopic motile structures.

● Other common asexual reproductive structures are `color{Violet}"conidia"` (Penicillium), `color{Violet}"buds"` (Hydra) and `color{Violet}"gemmules"` (sponge).

● Asexual reproduction is the `color{Violet}"common method of reproduction"` in these organisms with a `color{Violet}"relatively simple organisation"`, like algae and fungi but they shift to sexual method of reproduction just before the `color{Violet}"onset of adverse conditions"`.

C) BY VEGETATIVE PROPAGATION

`color{blue}"Vegetative Propagation/ Vegetative Reproduction"`: A type of `color{violet}"asexual reproduction"` employed by plants wherein `color{violet}"new independent individuals"` emerge from the `color{violet}"vegetative parts"` of plants, such as specialized stems, leaves, roots, and not from seeds or spores.

`color{blue}"Vegetative Propagules"`: In plants, the `color{violet}"structures"` which act as the `color{violet}"units of vegetative propagation"` such as runner, rhizome, sucker, tuber, offset, bulb, which are all capable of giving rise to `color{violet}"new plantlets"` are called vegetative propagules.


`color{green} ✍️ color{green} mathbf("KEY CONCEPT")`

● In animals and other simple organisms the term `color{Violet}"asexual"` is used unambiguously, in plants, the term `color{Violet}"vegetative reproduction"` is frequently used.

● In plants, the `color{Violet}"units of vegetative propagation"` such as runner, rhizome, sucker, tuber, offset, bulb are all capable of giving rise to new offspring.

● These structures are called `color{Violet}"vegetative propagules"`.

● Since the formation of these structures `color{Violet}"does not involve two parents"`, the process involved is asexual.

● Asexual (vegetative) as well as sexual modes of reproduction are exhibited by the `color{Violet}"higher plants"`.

● On the other hand, `color{Violet}"only sexual mode of reproduction"` is present in most of the animals.

SIGNIFICANCE IN REAL LIFE

● There is an infamous plant called the `color{Violet}"Scourge of the water bodies"` or the `color{Violet}"Terror of Bengal"`.

● This is nothing but the aquatic plant `color{Violet}"water hyacinth"` which is one of the `color{Violet}"most invasive weeds"` found growing wherever there is `color{Violet}"standing water"`.

● It `color{Violet}"drains oxygen"` from the water, which leads to `color{Violet}"death of fishes"`.

● Since it can propagate vegetatively at a `color{Violet}"phenomenal rate"` and `color{Violet}"spread all over"` the water body in a short period of time, it is very difficult to get rid of them.

● This plant was introduced in India because of its `color{Violet}"beautiful flowers"` and shape of leaves.



● Plants like potato, sugarcane, banana, ginger and dahlia are cultivated using methods of `color{Violet}"vegetative propagation"`.

● Here small plants emerge from the buds (called `color{Violet}"eyes"`) of the `color{Violet}"potato tuber"`, from the `color{Violet}"rhizomes of banana and ginger"`.

● These buds invariably arise from the `color{Violet}"nodes"` present in the `color{Violet}"modified"` stems of these plants.

● When the nodes come in contact with `color{Violet}"damp soil or water"`, they produce roots and new plants.



● Similarly, `color{Violet}"adventitious buds"` arise from the notches present at margins of leaves of `color{Violet}"Bryophyllum"`.

● This ability is fully exploited by gardeners and farmers for commercial propagation of such plants.


 
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