The discovery of cells was made possible, thanks to the invention of the microscope. It allowed the post-renaissance biologists to look at their specimen in greater detail, and eventually come up with the cell theory. Although previous models involving spherical lenses existed, Anton van Leeuwenhoek is credited with the invention of the first improved microscope. He used simple magnifying glasses that allowed up to 270x magnification.
Robert Hooke, in the year 1665, used a compound microscope of six-inch long to visualize specimen under reflected light. He noted the observations in his book, Micrographia. He observed thin slices of bottle cork and reported honeycomb-like structures which he called ‘cell’. However, his observations did not have any indication of the internal components of the cell. He could not explain their origin either. He attributed the growth of his specimens to natural or artificial heat and termed it spontaneous regeneration.
Later in 1676, Leeuwenhoek reported motility in the ‘animalcules’ he observed under his microscope. This led to a change in perspective towards the nature of cells and they were started to be considered as living. After this, more specimens of plants, molds and even bacteria from the tongue of ox were reported by Leeuwenhoek to the Royal Society. He was the first to observe that fertilization occurs when the sperm cells enter the egg cells. Thus he put an end to the theory of spontaneous regeneration, which was confirmed by Robert Hooke.
In the later decades, many biologists started observing different types of cells. Around this time biologists believed that there is a fundamental unit of life but they were unsure of what it was. About a hundred years later, Henri Dutrochet concluded that the cell is the fundamental physiological unit of organization of plants and animals.
This was probably the instance where the cornerstone of the foundation of a theory was laid. In 1838, a German botanist, Matthias Jakob Schleiden, observed that the tissues which constitute plants are made of different types of cells. The very next year, a British zoologist, Theodore Schwann reported the presence of a thin outer layer found in every cell.
The Cell Theory
The cell theory was prepared methodically by the observations and inferences of Schleiden and Schwann. They concluded that all living organisms are made up of one or more cells. However, it was Rudolf Virchow, in 1855, who explained that cells divide and give rise to new cells and gave the theory its final shape. Hence, the postulates of cell theory were laid as follows:-
- Cells arise from pre-existing cells.
- The cell is the basic functional unit of life.
- All living organisms are made up / constitute of one or more cells.
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