(Choice A) The rough endoplasmic reticulum has a stippled appearance secondary to the presence of numerous ribosomes bound to its membranes. These ribosomes are involved in the synthesis of integral membrane proteins and proteins destined for export or packaging into granules or organelles.
(Choice 8) The dark region identified within the nucleus is the nucleolus, the site of synthesis and assembly of eukaryotic ribosomal components. There is no lipid membrane separating the nucleolus from the rest of the nucleus.
(Choice C) The lighter “electron-lucent” regions within the nucleus signify euchromatin (unpackaged DNA being actively transcribed).
(Choice E) This electron-dense membrane-bound spherical structure represents an exocrine granule containing enzymes and other proteins packaged for secretion.