Nucleus 3–10 Largest organelle within the cell Surrounded by two membranes (nuclear with distinct boundary envelope) containing nuclear pore complexes and perinuclear cisternal space Often visible nucleoli and Regions with condensed and diffused chromatin pattern regions chromatin pattern (heterochromatin and euchromatin) Nucleolus 1–2 Roughly circular, basophilic Dense, nonmembranous structure region within the nucleus containing fbrillar and granular material Visible in living cells throughout interphase with interference microscopy Plasma membrane 0.008–0.01 Not visible External membrane and membranes surrounding membranous organelles of cell; two inner and outer electron-dense layers separated by intermediate electron-lucent layer rER Area 5–10 Often observed as basophilic Flattened sheets, sacs, and tubes of region of cytoplasm referred membranes with attached ribosomes to as ergastoplasm sER Throughout Not visible Flattened sheets, sacs, and tubes of cytoplasm Cytoplasm in region of sER may membranes without attached ribosomes exhibit distinct eosinophilia Golgi apparatus Area 5–10 Sometimes observed as Stack of fattened membrane sheets, “negative staining” region often adjacent to one side of nucleus Appears as network in heavy metal–stained preparations Visible in living cells with interference microscopy TABLE Review of Organelles and Cytoplasmic Inclusions: A Key to Light Microscopic and Electron Microscopic Identification2.1 Organelle or Inclusion Size (m) Light Microscopic Features Electron Microscopic Features continued next page chapter 2 Cell Cytoplasm MEMBRANOUS ORGANELLES TABLE Review of Organelles and Cytoplasmic Inclusions: A Key to Light Microscopic and Electron Microscopic Identification (Cont.)2.1 Organelle or Inclusion Size (m) Light Microscopic Features Electron Microscopic Features Secretory vesicles 0.050–1.0 Observed only when vesicles Many relatively small, membrane-bounded are very large (e.g., zymogen vesicles of uniform diameter, often granules in pancreas) polarized on one side of cell Mitochondria 0.2–7 Sometimes observed in Two-membrane system: Outer membrane favorable situations (e.g., liver and inner membrane arranged in numerous or nerve cells) as miniscule, dark folds (cristae) dots; visible in living cells stained In steroid-producing cells, inner membrane with vital dyes (e.g., Janus green) arranged in tubular cristae Endosomes 0.02–0.5 Not visible Tubulovesicular structures with subdivided lumen containing electron-lucent material or other smaller vesicles Lysosomes 0.2–0.5 Visible only after special enzyme Membrane-bounded vesicles, often electron histochemical staining dense Peroxisomes 0.2–0.5 Visible only after special enzyme Membrane-bounded vesicles, often with histochemical staining electron-dense crystalloid inclusions Cytoskeletal elements 0.006–0.025 Only observed when organized Long, linear staining pattern with width into large structures (e.g., muscle and features characteristic of each fbrils) flament type Ribosomes 0.025 Not visible Minute dark dots, often associated with the rER Glycogen 0.010–0.040 Observed as a “purple haze” Nonmembranous, extremely dense grapelike region of cytoplasm inclusions metachromasia with toluidine blue–stained specimen Lipid droplets 0.2–5, up Readily visible when extremely Nonmembranous inclusions to 80 large (e.g., in adipocytes) Generally appear as a void in the section Appear as large empty holes in section (lipid itself is usually removed by embedding solvents)
The plasma membrane is a lipid-bilayered structure visible with transmission electron microscopy.