4 Types of Asexual Reproduction

In this 4 types of asexual reproduction post we have briefly explained about forms of asexual reproduction; binary division, budding, fragmentation, and spore formation.

4 Types of Asexual Reproduction

Life of an organism is not infinite and during the life-span every organism needs to produce progeny to maintain existence. It is essential to maintain a high level of biodiversity and living stock. Asexual reproduction is a mode of reproduction in which a new offspring is produced by a single parent. The new individuals produced are genetically and physically identical to each other.

Forms of Asexual Reproduction

Binary division

Binary division is most common mode of cell division in bacteria. In this mode of cell division, a single bacteria cells grow transversely with the synthesis of chromosomal DNA. A transverse septum appears in the middle of the cell body and divides the bacterial cell into the two with a distribution of chromosomal DNA, ribosome and other cellular machinery.  

Asexual Reproduction

Forms of Asexual Reproduction: Binary division

A number of methds has been developed to measure bacterial growth in liquid media and in solid support media. A few are discussed below

Microscopic count: Bacterial cells can be counted easily on a “petroff-hausser counting chamber”. The chamber has a ruling to make square (1/400 mm2) of equivalent volume. A glass slide is placed (~1/50mm height) to make a chamber filled with bacterial cell suspension. Volume of each chamber is 1/20,000 mm3. This chamber can be used to observe bacteria with phase contrast microscope. For example, if each chamber has 8 bacteria then there are 8×20,000,000 or 1.6×108 bacteria/ml. A very high or low concentration of bacterial sample can not be counted accurately.

Plate count method: In this method, a defined amount of bacterial culture suspension is introduced onto solid support media to grow and give colonies. If number of colonies on solid media is too high, then serial dilution of original stock can be plated on solid media and number of colony can be counted with a colony counter. A manual colony counter has lamp at the bottom, a grid to divide the bacterial culture plate and a magnifying glass to visualize and count single colony. A plate with colony count of 30-300 can be used to determine the number of bacteria present in original stock.

Number of bacteria per ml =  Number of colonies counted on plate X dilution of sample

Turbidimetric methods: This method is based on light scattering principles of particulate matter such as bacteria. A bacteria cell suspension is placed in test cuvette and corresponding media in reference cuvette. The optical density or absorbance of the bacterial suspension is used to measure the number of bacteria number. This method can not distinguish between live or dead bacteria as both form contribute to the turbidity. 

Nitrogen content: A bacterial cell mass can be measured by direct measurement of dry weight of culture or nitrogen content.

Budding

In this mode of cell division, chromosomal DNA divides to form two copies. Sister chromosomal DNA moves to the one side of the cell and this portion of the cells protrude from main body to form bud. Eventually bud grows in size and get separated from main cell to develop a new cell.  

Asexual Reproduction

Forms of Asexual Reproduction: Budding

Fragmentation

This mode of asexual division is more common in filamentous bacteria. In this mode, filament of the growing cell gets fragmented into small bacillary or coccoid cells, these cellular fragments eventually develop into new cell. 

Asexual Reproduction

Forms of Asexual Reproduction: Fragmentation

Spore Formation

Spores are produced and give rise to new individual on germination. There are several kinds of spores and these are as follows:

Asexual Reproduction

Forms of Asexual Reproduction: Spore Formation Stages

Zoospores: These are motile and flagellated spores produced inside the zoosporangia. These are without cell wall and they utilizes the flagella to swim in water to disperse distant locations. These spores are found in fungi especially phycomycetes.

Sporangiospores: These are non-motile spores produced inside the sporangia. These spores are dispersed by wind and they germinate upon suitable conditions. These spores are found in fungi and they grow to give new mycelium. 

Chlamydospores: These are thick walled resting spores produced directly from hyphal cells. These spores are capable of storing large quantitity of food material and these spores are capable of storing for long period.

Oidia: In this condition, hyphae of growing fungi break open to form oidium which behaves like spores. These spores are thin walled and do not store large food material. The oidia are produced from fungi when they have excess water, sugar and certain salts. Upon immigrate release of oidia, they germinate to form new fungi otherwise these spore don’t survive harsh conditions.

Conidia: These are non-motile spores produced singly or a chains by constriction at the tip or lateral side of special hyphal branches, called conidiospores. They are produced exogenously, dispersed by wind and germinate directly giving out germ tubes.

Further Readings

Reference

4 Types of Asexual Reproduction