The cell theory states that all living things are made of cells . The Cell Theory is a fundamental principle of biology. 

Key Points of the Cell Theory:

  1. All living things are made up of cells. Cells are the smallest unit of life that can exist independently.
  2. Cells are the basic unit of life. Cells perform all the functions necessary for life, such as metabolism, growth, and reproduction.
  3. New cells arise only from existing cells. 


There are two main types of cells:

  1. Prokaryotic cells are the simplest type of cells and lack a nucleus or other membrane-bound organelles.
  2. Eukaryotic cells are more complex than prokaryotic cells and have a nucleus and other membrane-bound organelles.


types of cells

Living organisms can also be unicellular or multicellular. Unicellular organisms are made up of only one cell. Examples include some protests, bacteria, some fungi like yeast, and cells from the kingdom archaea.

Unicellular cells can be either prokaryotic or eukaryotic.

Prokaryotic cells don’t have an organized nucleus or membrane bound organelles like a mitochondria. The kingdom bacteria and archaea are made up exclusively of unicellular prokaryotic cells. 

Unicellular eukaryotic cells do contain a nucleus and membrane bound organelles. Examples include some protists like Euglena and Paramecium.

unicellular cells

Multicellular organisms contain two or more cells All multicellular organisms like this dog or lion tree, or flower are made of eukaryotic cells. 


Eukaryotic cells do contain a nucleus and membrane bound organelles.

So in summary, all living things are made of cells and they can be Unicellular and have one cell or multicellular and have two or more cells.