Asexual Reproduction, Clone & Vegetative Propagation

Here I discuss Asexual Reproduction, an important topic of NEET from the chapter 1st “Reproduction in Organisms” of the Biology Textbook for class 12 of NCERT publication.

Life Span & Life Cycle

An organism is immature when it takes birth. After that it grow and gain maturity gradually. When it become adult, taking part into Reproduction, produce new offspring. At the end, activity of the life is complete with death. This whole time period from birth to natural death of an organism is called Life Span.

If we consider the time period from birth to reproduction where a new life journey is to be started then we use the term Life Cycle.

Death of every indivisual is a certinity. Not a single one is immortal except single cell organisms. Unicelluler Organism like Monerans and Protists reproduce their offspring by dividing the parent cell into progeny cells that means parents are existed within their offsprings.

There is not any direct relation of life span with the body size of an organism. According to Biology NCERT text book “Life spans of organisms are not necessarily correlated with their sizes“.If we compare the body size of a parrot to a dog, A parrot is smaller than dog but it has a broad life span around 140 years where a dog is alive near about 20 to 25 years.

Reproduction

A biological process by which a parent gives birth progeny where the parent took birth from grandparent with the same process is called Reproduction. It maintain the species continuity by giving progeny generation after generation. In general, it has two methods namely Sexual and Asexual Reproduction. ‘Sexual‘ and ‘Asexual‘ both terms originate from the word ‘SEX‘ which is derived from a latin word ‘sexus‘ means ‘different‘.

Difference between Sexual and Asexual Reproduction

Firstly, Sexual means present sexuality. Sexual reproduction involve two different parrents come from two opposite sex. 
But in Asexual, ‘A’ means ‘absent’ and seuxual i.e. sexuality. Involvement of single parent is seen under Asexual reproduction.

Secondly, Sexual reproduction must go through gamet formation which is optional in Asexual reproduction.

Thirdly, Fusion of male and female gamet is prime criteria of Sexual reproduction.
But in Asexual reproduction, if gamet is formed in terms of ‘spore’, fusion of gamet is not happening.

Clone

A group of morphologically and genetically similer indivisuals come from single parent is called Clone.
It is a type of Asexual reproduction.
Here the offsprings are identical to one another as well as exact copies of the parent.

Types of Asexual Reproduction

Binary Fission

Many single cell organisms are divide into two halves, then each half rapidly grows and turn into mature organism. Amoeba, Paramecium etc. are reproduce by binarry fission.

Budding

Some organism devide unequally where the smaller part is act as ‘bud‘ which is remain attached initially to the biger part of parent body and eventually gets separated to become a mature body. This process is known as budding. It is seen in unicelluler yeast, multicelluler hydra etc.

Fragmentation

In hydra, sometime the body breaks into many fragments where all the fragments grow into adult in later. The process is called Fragmentation.

Encystation & Sporulation

Amoeba normally perform binary fission. But when environment is unfavourable, Amoeba withdraws its pseudopodia and form a three-layered hard covering called ‘cyst‘. This is termed as Encystation.

When the condition become favourable, encysted Amoeba forms pseudopodiospore by multiple fission. After that the cyst wall bursts out and the spores release into surrounding. finally the spores are converted into mature Amoeba. The process is known as Sporulation.

Special Asexual structure

there are so many special asexual reproductive structure are formed during asexual reproduction. Zoospore, a microscopic motile structures, is the most common type of asexual structure generally fond in Chlamydomonus. Conidia is seen in Penicillium. Sponge forms Gemmules for this purpose.

Vegetative Propagation

The term ‘vegetative‘ comes from ‘vegetation‘ that means a group of plants found on a habitat. When a plant group is propagated from its habitat through asexual reproduction then it is called as Vegetative Propagation.

The unit of vegetative propagation is called Vegetative Propagules.

Some famous vegetative propagules are runner (Grass), sucker (Mint), tuber (Potato), rhizome (Ginger, Banana), bulb (Onion) and offset (Eichhornia).

Eichhornia crassipes is an aquatic plant. It grow in standing water. It drains oxygen from the water which leads to death other aquatic organisms. It is named as “Water Hyacinth” and “scourge of the water bodies“.

It propagate at a phenomenal rate throughout the water bodies within short time period and become very difficult to get rid off from the weed. So, It is the most invasive weeds.
It was introduced in India for its beautiful fleowers and shape of leaves.

At the first time, it polluted so many pond in Bengal by draining oxygen form water which cause death of other aquatic organisms. Thats why it is famous as “Terror of Bengal“.

Thanks for reading……