The cell theory forms a basis for the way that biologists may now study living things. The cell theory states that:
Just how the cell theory became a theory is not too much of a mystery. A Scottish biologist named Robert Brown was the first to discover the nucleus of a cell using one of the very first microscopes called the light microscope. Eventually, a German biologist named Matthias Schleiden used Brown's research to learn more about the cell and its nucleus. After several observations, Schleiden found that cell's nuclei must play important roles in cell reproduction. Finally came German physician Rudolf Virchow who proposed that animal and plant cells are produced only by the division of cells that already exist.
After years and years of observations, the cell theory became an extremely popular method for biologists to observe organisms with. Now we know that the cell theory applies to every single organism that there is in the world! Whether an organism is made up of only one cell or millions of cells, it's still made up of cells, right? The best way to get a good look at artificial cells is to scrape a few shavings off of a cork screw, and take a look at it under a microscope.