Elucidating the structure of dna
All living organisms are composed of cells, and all cells arise from other cells.
These simple and powerful statements form the basis of the cell theory, first formulated by a group of European biologists in the mid-1800s.
So fundamental are these ideas to biology that it is easy to forget they were not always thought to be true.
Grew likened the cellular spaces to the gas bubbles in rising bread and suggested they may have formed through a similar process.
The presence of cells in animal tissue was demonstrated later than in plants because the thin sections needed for viewing under the microscope are more difficult to prepare for animal tissues.
The prevalent view of Hooke's contemporaries was that animals were composed of several types of fibers, the various properties of which accounted for the differences among tissues.
At the time, virtually all biologists were convinced that organisms were composed of some type of fundamental unit, and it was these "atomistic" preconceptions that drove them to look for such units.
While improvements in microscopy made their observations better, it was the underlying belief that there was some fundamental substructure that made the microscope the instrument of choice in the study of life.In 1676 the Dutch microscopist Antony van Leeuwenhoek (1632–1723) published his observations of single-cell organisms, or "little animalcules" as he called them.It is likely that Leeuwenhoek was the first person to observe a red blood cell and a sperm cell.Leeuwenhoek made numerous and detailed observations on his microorganisms, but more than one hundred years passed before a connection was made between the obviously cellular structure of these creatures and the existence of cells in animals or plants.