Mitochondria consist of an outer membrane and a highly folded inner membrane and are generally tubular in shape.

• Mitochondria are usually not seen with the LM unless special stains or histochemical techniques are used (Fig. 2-11).
• Histochemical staining here uses specific enzymes of the citric acid cycle, which are only found in mitochondria, to generate the color seen.
  • Examine ultrastructural views of mitochondria in Figures 2-12 and 2-20b.

Why are mitochondria sometimes considered to be “semiautonomous”, compared to other organelles?

What is the functional significance of the mitochondrial cristae? Of the mitochondrial matrix?

Less fundamentally important than the organelles mentioned so far, inclusions are cytoplasmic accumulations of various cell products which are not membrane-bound.

• Examples are lipid droplets, glycogen granules, and melanin granules (all shown in Fig. 2-35.)
• Lipid requires special fixation and staining to be seen, glycogen usually requires a special stain, but melanin requires no stain.

Why are the three types of inclusions listed above not found in all cells?

The next unit deals with stem cells and apoptosis.