Introduction

Biological cells are basic units in life. They are composed of a huge number of biological molecules, such as proteins, nucleic acids, lipids, sugar and organic molecules and inorganic ions. The biological macromolecules form well-organized compartments, so-called organelle. The ultimate goal of cell biology would be the complete illustration of cellular events at high spatial and temporal resolutions. To illustrate spatiotemporal events in biological cells, various methods for microscopic observation have been innovated. Here, prior to introduced X-ray diffraction imaging (XDI), typical microscopic methods are introduced for visualizing the internal structures of cells, such as light microscopy, transmission electron microscopy, and X-ray imaging techniques. In addition, possible roles of XDI in visualizing cells are described.