Question

Explain with examples types of asexual reproduction in unicellular organisms.

Answer 1

Asexual reproduction occurs in unicellular organisms through various methods. Some of these methods are as follows:

1. Binary Fission: In this method, the parent cell divides into two equal parts, resulting in the formation of two new daughter cells. This division occurs through mitotic division. Generally, binary fission occurs in favourable conditions when sufficient food is available. Bacteria, protozoa, mitochondria, and chloroplasts reproduce asexually through binary fission.
   Depending on the axis of division, binary fission in different protozoa is classified as:
   1. Simple Binary Fission: Since Amoeba does not have a definite shape, it can divide along any axis. Therefore, this type of fission is called simple binary fission.
      Example: Amoeba
      
   2. Transverse (Horizontal) Binary Fission: In Paramecium, division occurs along the transverse axis.
      Example: Paramecium
      
   3. Longitudinal (Vertical) Binary Fission: In Euglena, division occurs along the longitudinal axis.
      Example: Euglena
      
2. Multiple Fission: Amoeba and similar unicellular protozoa reproduce asexually through multiple fission in unfavourable conditions. When food is insufficient or environmental conditions become unfavourable, Amoeba stops moving and does not produce pseudopodia. It becomes spherical and forms a hard protective covering around itself, known as a “Cyst”.
   Inside the cyst, the nucleus undergoes multiple mitotic divisions, resulting in the formation of several nuclei. Later, the cytoplasm also divides, producing multiple small Amoebae. These remain inside the cyst until favourable conditions return. Once conditions improve, the cyst bursts, releasing several young Amoebae.
   
3. Budding: Yeast reproduces asexually through budding. First, mitotic division occurs in the parent cell, producing two daughter nuclei. A small outgrowth, called a "Bud", appears on the parent cell. One of the daughter nuclei enters this bud. After growing sufficiently, the bud detaches from the parent cell and starts developing as an independent yeast cell.