Specimens are usually first fixed and then embedded with wax or resin before sectioning. Uptake of I-131 by the thyroid gland indicates the metabolism level of that gland. All membranes, nuclear, cytoplasmic, mitochondrial, endoplasmic, etc. appear to display a similar structural pattern. The outer triplets are microtubules, but the pair of tubules in the center are NOT microtubules. Certain simple organisms lack cellular separations.
Viruses lack cellular organization.
These processes go down the energy hill. Permeases have been associated with the movement of glucose in various body regions. Prokaryotes do NOT have membrane bound organelles. Prokaryotic ribosomes are smaller. Cell walls are made up of different carbohydrates and polypeptides than cellulose.