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Living cells, as opposed to hard condensed matter samples are soft and do not always adhere well to surfaces. The typical size of cells is a few microns while the proteins are smaller, in the range of tens of angstroms.

Living cells are divided into two types-prokaryotic and eukaryotic and this division is based on internal complexity. The eukaryotic cells are highly structured and include the cells of protozoa, higher plants and animals. These cells are larger than the cells of bacteria, and have developed specialized packaging and transport mechanisms that are required to support their larger size. The prokaryotic cells are simple in structure, with no recognizable organelles. They have an outer cell wall that gives them shape. Under the rigid cell wall is the cell membrane. The cytoplasm enclosed within the cell membrane does not exhibit complex structure when imaged by electron microscopy.