Section 1: The Discovery of Cells
Cells are amazing things. They are the smallest, most basic unit of all living things; they are the building blocks of life. Cells can be simple, like those found in bacteria, or complex, like those found in plants and animals. But without the development of the microscope, cells would have remained invisible throughout most of human history.
A compound microscope, like those used in a biology lab, uses two or more lenses to enlarge or magnify an object. In 1665, a scientist named Robert Hook used an early compound microscope to look at a cork slice and coined the term “cell” to describe the tissue. The continued development of more microscopes allowed scientists to see that cells were composed of many parts with many functions. The development of an electron microscope, which uses electromagnetic fields, allows objects to be magnified up to 500,000 times using beams of electrons instead of light. The transmission electron microscope (TEM) allows scientists to see structures inside of a cell. The scanning electron microscope (SEM) enables scientists to see a cell’s three-dimensional shape, which allows them to study a cell’s surface. A scanning probe microscope produces images by tracing the surface of a cell or structure with a probe.
With the development of microscopes, scientists were able to observe and learn more about cells, creating a fundamental concept of biology. Cell theory was developed out of their conclusions. Cell theory has three main components. First, all living things are made of one or more cells. Secondly, cells are the basic unit of structure and function in all living things. Finally, all cells come from other cells.
All cells contain small structures called organelles. Each organelle has a specific function in the cell. There are two distinct types of cells called prokaryotic and eukaryotic. Prokaryotic cells were the first to evolve. They lack a true nucleus and other membrane bound organelles. They tend to be smaller and simpler. Bacteria and archaea are examples of prokaryotic cells. Eukaryotic cells are similar to each other, and all have a nucleus surrounded by a membrane and other membrane bound organelles. Protists, fungi, plants, and animals are all eukaryotic cells.