Multiple Choice
Which of the following best describes the fluid mosaic model of biological membranes?
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6. The Membrane
Biological Membranes
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When observing a cell under a brightfield microscope, how is the cell membrane typically identified?
A
As a thin, dark outline surrounding the cell due to differences in refractive index
B
As a region with no visible boundary between the cell and its environment
C
As a brightly colored structure due to natural pigmentation
D
As a thick, multilayered band visible without staining
Verified step by step guidance1
Understand the principle of brightfield microscopy: Brightfield microscopy relies on differences in refractive index and light absorption to create contrast in unstained specimens.
Recall the structure of the cell membrane: The cell membrane is a thin, phospholipid bilayer that separates the cell's interior from its external environment.
Consider how the cell membrane appears under brightfield microscopy: Due to its thin structure and the refractive index difference between the membrane and surrounding medium, the cell membrane typically appears as a thin, dark outline.
Eliminate incorrect options: Brightfield microscopy does not show natural pigmentation unless the cell is stained, and the cell membrane is not thick or multilayered. Additionally, the cell membrane does not blend seamlessly with the environment under this type of microscopy.
Conclude that the correct identification of the cell membrane under brightfield microscopy is as a thin, dark outline surrounding the cell due to differences in refractive index.
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