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3.1c
| Question | Answer |
|---|---|
| In the nineteenth century, little was known about cells except that they were enclosed in a membrane and contained a nucleus. | The fluid between the nucleus and surface membrane, its cytoplasm, was thought to be little more than a gelatinous mixture of chemicals and vaguely defined particles. |
| The transmission electron microscope (TEM), invented in the mid-twentieth century, radically changed this view. | Using a beam of electrons in place of light, the TEM enabled biologists to see a cell’s ultrastructure, a fine degree of detail extending even to the molecular level. |
| The most important thing about a good microscope isn’t magnification but resolution—the ability to reveal detail, to distinguish small, close-together objects from each other. | Any image can be photographed and enlarged as much as we wish, but if enlargement fails to reveal any more useful detail, it is empty magnification. |
| A big blurry image isn’t nearly as informative as one that’s small and sharp. The TEM reveals far more detail than the light microscope (LM) (fig. 3.3). | A later invention, the scanning electron microscope (SEM), produces dramatic three-dimensional images at high magnification and resolution (see fig. 3.10a), but can view only surface features. |
| FIGURE 3.3 Magnification Versus Resolution: Cross sections of a skeletal muscle cell viewed by (a) light microscopy (LM) and (b) transmission electron microscopy (TEM) | The TEM, with its better resolution, shows significantly finer detail, down to the protein filaments that produce muscle contraction. |
| A stunning application of SEM, often seen in this book, is the vascular corrosion cast technique for visualizing the blood vessels of an organ. The vessels are drained and flushed with saline, then carefully filled with a resin | After the resin solidifies, the actual tissue is dissolved with a corrosive agent such as potassium hydroxide. This leaves only a resin cast of the vessels, which is then photographed with the SEM. |
| SEM | The resulting images are not only strikingly beautiful, but also give great insights into the blood supply to an organ from macro- to microscopic levels |
| The cytoplasm is crowded with fibers, tubules, passages, and compartments. It contains the cytoskeleton, a supportive framework of protein filaments and tubules; an abundance of organelles | diverse structures that perform various metabolic tasks for the cell; and inclusions, which are foreign matter or stored cell products. |
| A cell may have 10 billion protein molecules, including potent enzymes with the potential to destroy the cell if they’re not contained and isolated from other cellular components. | You can imagine the enormous problem of keeping track of all this material, directing molecules to the correct destinations, maintaining order against nature’s incessant trend toward disorder. |
| Cells | maintain order partly by compartmentalizing their contents in the organelles. |
| The cytoskeleton, organelles, and inclusions are embedded in a clear fluid called the cytosol or intracellular fluid (ICF). | All body fluids not contained in the cells are collectively called the extracellular fluid (ECF). |
| The ECF located amid the cells is also called tissue (interstitial) fluid. | Some other extracellular fluids include blood plasma, lymph, and cerebrospinal fluid. |
| In summary, we regard cells as having the following major components: | Plasma membrane Cytoplasm Cytoskeleton Organelles (including nucleus) Inclusions Cytosol |
| Plasma membrane | ------ Cytoplasm Cytoskeleton Organelles (including nucleus) Inclusions Cytosol |
| Cytoplasm | Plasma membrane ----- Cytoskeleton Organelles (including nucleus) Inclusions Cytosol |
| Cytoskeleton | Plasma membrane Cytoplasm ------ Organelles (including nucleus) Inclusions Cytosol |
| Organelles (including nucleus) | Plasma membrane Cytoplasm Cytoskeleton ------ Inclusions Cytosol |
| Inclusions | Plasma membrane Cytoplasm Cytoskeleton Organelles (including nucleus) ----- Cytosol |
| Cytosol | Plasma membrane Cytoplasm Cytoskeleton Organelles (including nucleus) Inclusions ------ |
| What are the basic principles of the cell theory?: All living organisms are made of one or more cells. | Cells are the basic structural and functional units of all life. All activities of an organism stem from the activities of its cells. All cells arise from preexisting cells and pass hereditary information to the next generation. |
| Squamous: | Thin, flat, and scaly in shape. |
| Stellate: | Having a star-like shape with multiple pointed processes. |
| Columnar: | Distinctly taller than it is wide. |
| Fusiform: | Spindle-shaped; elongated with a thick middle and tapered ends. |
| Why can’t cells grow to unlimited size? | Cell size is limited primarily by the surface area to volume ratio. As a cell grows, its volume (and thus its metabolic needs) increases faster than its surface area (the membrane available for nutrient/waste exchange) |
| Why can’t cells grow to unlimited size? | A cell that is too large would not have enough membrane to support its volume. Additionally, diffusion of molecules within an overly large cell would be too slow to support its metabolism. |
| Cytoplasm | is a collective term for all the contents of a cell between the plasma membrane and the nucleus (including the cytoskeleton, organelles, inclusions, and the fluid). |
| Cytosol (or intracellular fluid) | is specifically the clear fluid in which the cytoskeleton, organelles, and inclusions are embedded. |
| Intracellular Fluid (ICF) | The fluid contained within cells; also called cytosol. |
| Extracellular Fluid (ECF) | All body fluids not contained inside cells. This includes tissue (interstitial) fluid, blood plasma, lymph, and cerebrospinal fluid. |
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Russells3709