Observation of live cells under improved mcirosocope.
Explanation:
The cells were first discovered in the year 1665 by Robert Hooke using a coarse compound microscope but what h observed were dead cork cells.
It was Anton van Leeuwenhoek who observed live cells under the microscope that had magnification which was about 300 times more than the one used by Hooke.
By observing cells he was able to observe motility of unicellular organisms, fertilization process in eukaryotes by observing the fusion of sperm and egg among many other things.
