Abstract
Every element of life, at all levels of hierarchy down to a single molecule, is a functional entity that by itself performs a delicate task (s). Understanding of the mechanism of biological machinery therefore requires a close observation of the performance of individual cells, organelles, or molecules. Three examples are presented, in which single-cell or single-molecule observation under an optical microscope was crucial in the analysis: ionic regulation of the acrosome reaction in starfish sperm revealed by multi-view microscopy, elucidation of elementary steps of actomyosin motors using optical tweezers, and detection of molecular rotation via single fluorophore imaging.
