All living things are made up of cells. They are the basic structural and functional units of life. Robert Hooke discovered the cell in 1665. The average size of a cell varies between 10 micrometers (µm) to 150 micrometers (µm).
- The simplest living organisms are made up of one cell only. These organisms are described as UNICELLULAR organisms. E.g. Bacteria
- Most other living organisms have many cells and are described as MULTICELLULAR organisms. E.g. Birds
A cell is a very small piece of transparent jelly-like substance, surrounded by a thin covering. The jelly is called the cytoplasm. The covering is called the cell membrane. Most of the cells also have dark area inside the cell called a nucleus