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When we see any cell under a microscope the membrane surrounding the cell is opaque. But then if the cell membrane surrounds the cell in all the three dimensions how come we can see through the cell membrane and have a look at the organelles inside if the membrane is also covering the cell from the top and not just at the boundries on the object plane.

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    $\begingroup$ A little simplified: a glass (say a glass of water) is clear, yet if you look at it level with the water level, the sides are dark, as is the top of the water. Swiveling the glass doesn't change anything; the glass and water are very clear, but where there is an increase in the sheer amount of clear matter in the same plane, it appears darker. Same principle. $\endgroup$ – anongoodnurse Nov 8 '16 at 22:56
  • $\begingroup$ If you can see the cell's insides, the cell membrane is, obviously, not nontransparent $\endgroup$ – AliceD Nov 15 '16 at 22:59
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The membrane(and associated proteins) isn't actually opaque, it is just "more opaque" or "less translucent" than the cytosol: when you look through the microscope, you are utilizing this contrast to detect the edges.

In the center of the cell you observe, you see the membrane straight-on, and light is only affected by 1-2 layers of membrane. On the edge, you are viewing through the membrane somewhat "sideways" , so there is effectively more "thickness" of membrane. Maybe not an exact replica of the situation, but one that might be easier to visualize, is earth's atmosphere viewed from space. You can see the "blueness" of the atmosphere at the edges, but when you look straight down at the ground you see clouds, oceans, landmasses not tinted as blue.

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  • $\begingroup$ I'm not sure if this answers my question. What I think of a cell is a three dimensional object surrounded by a cell membrane. Now if on looking at a cell 2 of microscope I can see the cytosol then it probably means that the cell membrane that should have been between the microscope and the cytosol is transparent but then how come at the same time I see the cell membrane in the same image as a dark boundary surrounding the cytosol. $\endgroup$ – Hemant Kumar Nov 8 '16 at 23:26
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    $\begingroup$ In the center of the cell you observe, you see the membrane straight-on, and light is only affected by 1-2 layers of membrane. On the edge, you are viewing through the membrane somewhat "sideways" , so there is effectively more "thickness" of membrane. Maybe not an exact replica of the situation, but one that might be easier to visualize, is earth's atmosphere viewed from space. You can see the "blueness" of the atmosphere at the edges, but when you look straight down at the ground you see clouds, oceans, landmasses not tinted as blue. $\endgroup$ – Bryan Krause Nov 8 '16 at 23:32

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