Ultrastructure is the detailed structure of a biological specimen, such as a cell, tissue, or organ, that can be by electron microscopy. Cells in culture, stained for keratin (red) and DNA (green) The cell is the structural and functional unit of all living organisms, sometimes called the building blocks of life. ... Biological tissue is a group of cells that perform a similar function. ... In biology, an organ (Latin organum: instrument, tool) is a group of tissues, which perform a specific function or group of functions. ... The electron microscope is a microscope that can magnify very small details with high resolving power due to the use of electrons rather than light to scatter off material, magnifying at levels up to 500,000 times. ...