All the organisms that we see around us have a certain time limit of survival. The period from birth to death of the living being is called life span. Some organisms have a life as short as one day, and some live even more than a hundred years. You must have observed that often life span of any living being is not related to the size. Even a small parrot can live for more years than a tiger. The crows and sparrows show a significant life span difference even though both are birds.
Similarly, a peepal tree has much more life span than a mango tree. However, one certain thing is the ‘mortality’ of these organisms. No living being is immortal, except unicellular organisms. Further, we will discuss, how these single-celled organisms continue to live while many big and advanced creatures can’t.
What is reproduction?
It is a physiological process in which an organism gives rise to offsprings (young ones) that are somewhat similar to itself. The offspring also go through the same cycle of growth, maturation and then produce a new offspring. Thus, the cycle of birth, growth, and death continues generation after generation.
There is a large variety in the biological world, and each living being has developed its way to multiply and produce its next generations.
Factors that affect how organism reproduce are:
- Internal physiology of an organism
In this method, a single parent (individual) give rise to offspring. As a result, the offsprings are not only similar to each other but are exactly the same as their parents. These organisms are often termed as clone because these are both morphologically and genetically identical. Asexual reproduction is most commonly found in single-celled organisms. It is also found in some plants and animals that have relatively simple cellular structures. In Monerans and Protists, the parent cell divides into two cells and give rise to new individuals. Thus, in these living beings cell division is the mode of producing (reproduction).
The division of an organism in two individuals is called binary fission. A significant number of single-celled organisms reproduce by this method. The two new formed individuals rapidly grow and become an adult and again divide to form another new individual. This process continues giving rise to new generations.
Reproduction in Yeast
The reproduction by this organism is simple and is done by unequal division of genetic material. The material is distributed to the small bud which remains attached to the parent cell initially and eventually gets separated and go through maturation.
Reproduction in Amoeba
Amoeba goes through some simple phases in its lifespan.
In unfavourable conditions, there is a withdrawal of pseudopodia by Amoeba and a cyst (three-layered hard covering) is formed around Amoeba. This is called encystation.
When the favourable environment surrounds this organism, it starts multiple fission in which many small amoebae (also called pseudopodiospores) are produced breaking the cyst it had formed in unfavourable conditions.
Numerous spores are released in the surrounding medium that undergoes a growing process and develops into an adult amoeba. This method of reproduction is known as
Some other modes of asexual reproduction
Some organisms that belong to the Kingdom Fungi or simple plants like algae possess certain asexual structures for reproduction. These structures are generally known as Zoospores. There are very tiny and microscopic. These zoospores are motile i.e. they can move.
- Conidia is the asexual structure found in Fungi like Penicillium.
- Buds are found in Hydra and Yeast
- Gemmules are found in sponges.
- Plants reproduce asexually through vegetative reproduction. This includes the units like runner, sucker, bulb, offset, a rhizome that gives rise to offsprings and these structures are termed as vegetative propagules.
- Fragmentation is the method of reproduction in some organisms like Hydra in which the body of the organism when broken down in pieces can give rise to a new fully grown organism. This is also a kind of asexual reproduction since only one parent is involved.