ultrastructure

This term is used exclusively within high-level scientific and medical discourse, specifically in histology and cell biology. It refers to the architecture of a cell or tissue at a scale that exceeds the resolution of light microscopy, necessitating the use of electron microscopy to visualize organelles and molecular complexes.

Because it describes a specific level of biological organization, it is typically treated as an uncountable noun when referring to the general concept of microscopic architecture. However, it can be used as a countable noun when referring to the specific structural arrangements of different specimens or distinct types of cellular organization.