Robert Hooke was an English scientist that was the first one to see a cell under a microscope. In 1655, he explored a cork, which consisted out of the walls of the dead cells.

Electron micrographs are black and white, which makes certain structures difficult to see. Therefore, a computer adds false coloring, so these structures would be more obvious.

The nucleus is an organelle found in eukaryotes that contain DNA molecules. However, it is not a part of the prokaryotes, which makes the main difference between these two types of organisms. Eukaryotes, such as plants or mammals, are bigger and more complicated than prokaryotes, such as bacteria.

The cell theory states that all the living things are composed of cells, which are their basic functional and structural units, and that all cells originate from the ones that already exist.
Several scientists had an impact on the cell theory, but Matthias Schleiden, Theodor Schwann, and Rudolph Virchow were the ones who formulated it. The cell theory is one of the fundamental principles of biology.
Robert Hooke was an English scientist that was the first one to see a cell under a microscope. In 1655, he explored a cork, which consisted out of the walls of the dead cells.
Anton Van Leeuwenhoek has improved a microscope and was the first to describe bacteria and yeast. He was also the first one to explore the drop of water and capillary blood under a microscope.
In 1838, Matthias Schleiden noticed that the plants are made of cells, while
In 1839, Theodor Schwann concluded that the structural unit of all animals is also the cell.
In 1855, Rudolph Virchow presumed that all cells originate from pre-existing cells.

If we observe a structure under a microscope, we should wonder what are we looking at – an organism or a non-living object. Every organism is made of structural and functional units that are known as cells. If we find them in the observed structure, we are sure that it is a living organism.

We differ a light and electron microscope.
The light microscope uses light waves that pass through the magnifying lenses to the specimen. Since the light waves diffract, we can observe thin specimens that are magnified up to 1000 times. These specimens must be very thin and they are usually transparent, so sometimes chemical colors must bind to the examined structure, so it would be visible.
There are two types of an electron microscope – transmission (TEM) and scanning electron microscopes (SEM). We can observe extremely thin slices of the specimen under a TEM, which gives us a black and white picture. In order to make certain structures visible, colors are added by the computer, which is known as “false coloring”. They give us a two-dimensional image. However, an electron beam of the SEM passes over the surface of the observed specimen, so we get a three-dimensional image.