Why do cells, and organelles appear cross-sectioned or “split” in microscopic images? Do they ever appear whole?
In: Biology
Because they are actually physically cross-sectioned before viewing under the microscope.
Tissue prepped for histology need to be stained (cells are normally clear), fixed (so cells don’t move around for the next step), and then sectioned (tissue is too thick to image under a microscope). The sectioning step uses a microtome which cuts the tissue into extremely thin sections of a few microns from 2-10 um. The average animal cell is 10-20 um in diameter so it’s most likely the microtome will slice through a cell and it’s organelles.
For organelles to appear whole, you have to avoid sectioning them. Even if you compare adjacent sections, the cells may have detached differently from the physical cutting force so you can’t easily align a cell from one section to the other half of the cell in another section. One method uses laser confocal imaging to image one depth layer of a full piece of tissue at a time. Performing this for many layers gives you a 3D volume of the cell so organelles can be whole.
This allows us to see the true organelle shape. Recent imaging of mitochondria revealed that they actually have a snake-like appearance inside the cells rather than small ovals. The small ovals were due to sectioning cutting through their true snake-like shape.
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