Question

How organisms have been classified on the basis of the number of cells?

Answer 1

There is a diversity of organisms on earth. This makes the study difficult. So they all have been characterized on the basis of some particularities to make the study and their differentiation easier. This may form a large group but makes it convenient to separate them from the others. This could be on the basis of morphology, habitat, number, etc.

Step by step answer: Cells form the structural and functional unit of life. All the creatures are made up of the cell. The cells perform all the metabolisms of life thus whatever the number of cells may be, the organism will carry out the basic metabolisms at least.
On the basis of number, the living organisms are divided into –
1. Unicellular
2. Multicellular
Unicellular organisms are the ones that have only one cell as their functional and structural unit. This single cell is responsible for all the activities like respiration, excretion, etc. they do not have complexity in their metabolism. They are primitive organisms. They are usually not visible to the naked eye. For example - protozoa, unicellular algae, and fungi, etc.
Multicellular organisms are made of many cells. They have little complex structures and metabolisms. They are mostly visible to the naked eye. They grow from a single cell and develop into a whole multicellular organism. For example- plants and animals. Their body has differentiated cells to perform functions like respiration, excretion, digestion, etc.

Note: Prokaryotes are unicellular organisms but the eukaryotes can be both unicellular or multicellular. Prokaryotes do not have a nucleus but contain genetic material and information. They usually divide or reproduce by asexual means in which only one parent is involved. The eukaryotes have a well defined and membrane nucleus.