Compared with a plasma membrane, a human red blood cell is roughly:

1. Red blood cells are visible under a light microscope but membranes are not. 2. Human red blood cells are approximately 8 micrometres wide. 3. That is approximately 1,000 times wider than a plasma membrane. 4. The gap in scale is why membrane structure had to wait for electron microscopy. _Source: OpenStax Biology for AP(R) Courses (CC BY 4.0), Ch 5 'Structure and Function of Plasma Membranes', sections 5.1-5.4_