Every living thing is made up of cells. The cell is the smallest unit with the basic properties of life. Bacteria and yeast consist of only one cell. Plants and animals have many billions of cells. Human beings are made up of more than 75 trillion cells. Only viruses – pathogens of some infectious diseases (for example, influenza, measles, smallpox) – are not cells and do not consist of cells. But they can multiply only in a living cell.
The cell was first discovered by the English physicist Robert Hooke in 1665. He designed microscopes, which gave 140 times increase. Once, examining the thin sections of the cork, he saw that the whole cork consisted of pores. These were the cells.