Every living body is composed of cell. Some living bodies are made of only one cell. They are called unicellular organism, e.g. Bacteria,Amoeba,Plasmodium, some Fungi and some Algae. Some living bodies are made ofmore than one cell. These are called multicellular organism. There are many living bodies, which are made of millions of cells. Living bodies like human. beings or mango tree etc. are composed of millions of cells. Unicellular organisms increase their number (multiply) by cell division. In this process one cell divides into two, two to four and so on. In multicellular organisms, a large body consisting of millions of cells develops by cell division from the embryo, which also develops from a single fertilized egg. A young seedling developed to a large tree by cell division. Again new generation is created from male and female gametes formed by cell division. But all these divisions are, not alike. The processes of division are of different types and the results are also different.
Types of cell division:
Cell division is of three types: (i) Amitosis (ii) Mitosis and (iii) Meiosis.
1. Amitosis: This type of cell division occurs in unicellular prokaryoticorganisms like Bacteria, Yeast etc. In this division, at first the nuclear materials are directly splitted into two portions and then the cell divides into two from the middle region. As a result, from one cell there' develops two.
2. Mitosis: Mitosis is a type of cell division by which a eukaryotic cell dividesinto two by a special method. In this process, the nucleus and chromosome are divided once and the number, structure and properties of chromosome in the newly formed cell remain just alike the mother.
cell. Mitosis is also termed as equational division. Normally this division occurs in somatic cell. As a result of this division, the plant and animal increases in length and breadth. Mitosis occurs in all meristamatic cells of plants.
3. Meiosis: Meiosis is a type of cell division by which a Eukaryotic celldivides into four cells by a special method. In this process the nucleus divides twice but the chromosome divides once. The number of chromosome in the newly formed daughter cell reduces to the half the number of mother cell. As the number of chromosome reduces to half this process is also termed as reduction division. In Greek `Meiosis' means `to reduce' and from this the term Meiosis comes in use. This division occurs in reproductive mother cells of diploid organisms. As a result haploid gametes develop. In haploid organisms, this. division occurs in the zygote, as a result of which the organism becomes haploid again.