Summary

[Bernard NebelKeymaster]

When students view a cell membrane under their microscopes all they see is a thin dark line, but have them visualize the tremendous structural and functional complexity of this “envelope.” This “thin dark line” is in fact a double layer of complex molecules (phospholipids) with “heads” to the outside and tails to the inside and with various proteins imbedded in polk-a-dot fashion. (They should note how this molecular complexity, which they could hardly measure, speaks to the incredibly tiny size of atoms and molecules.)

Then they should visualize that membrane is far from a passive envelope. It uses cellular energy (ATP) to pump certain ions (K⁺ and Cl^–) in and out. It allows passive diffusion of CO2 and O2 and facilitated diffusion of water. Finally, it is capable changing its contours such that it can physically engulf or secrete materials, endo- and exocytosis.

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