Robert Hooke was an English natural philosopher, architect nd polymath who applied the word "cell" to describe the smallest unit of life.
Francesco Redi was the first to disprove the theory of spontaneous generation, and discovered that living things have to be created from other living things.
In one experiment, Redi took 6 jars, which he split into 2 groups of three: in the first jar of each group he put an unknown object, in the second a dead fish and in the third a raw chunk of meat. He then covered the first group of three with a fine cloth so only air could get in and left the other group of three open. After several days he saw that maggots only appeared on the objects in open jars, on which flies could land and lay eggs.
Anton van Leeuwenhoek was a Dutch tradesman and scientist, best known for his work and creation of the microscope and his discoveries towards single-celled organisms.
After creating powerful microscope lenses and applying them to his knowledge of biology he examined bee stings and mouth parts, after which he discovered single-celled organisms.
These two scientists both had discoveries of their own to begin with. Schleiden's being that plants contained cells, and Schwann's being that cells are also in animals. Together with these discoveries and previous knowledge they wrote the cell theory:
All organisms are composed of at least one cell
Cells form the basic organizational structure of all living things
All cells come from pre-existing cells.
This theory completely blew Aristotle's theory of spontaneous generation away, convincing all that this is now what is correct.
Virchow's most widely known contribution was his development on cell theory. He was cited for being the first to recognize leukemia cells and that all cells came from pre-existing cells. At first Virchow did not believe the evidence for cell division, that it only occurs in certain types of cells.
Louis Pasteur’s pasteurization experiment illustrates the fact that the cause of liquid to spoil was caused by particles in the air rather than the air itself.
Pasteur conducted multiple experiments proving his theory, one of which is the swan flasks. Pasteur had boiled broth and placed in into two separate flasks, The first flask had a swan neck attached to the flask, the second one, the neck was removed, opening it up to particles. He then waited and noticed that the flask with no neck had already spoiled while the swan necked flask was still fine. Thus concluding that it was the particles spoiling liquids not the air itself.