Biology / Unit 2 Bio 0333 short lesson, about 20 seconds
Selective Permeability
Captions available
The idea
A plasma membrane is selectively permeable, letting some substances cross freely while blocking others based largely on size and polarity.
In practice
Small, nonpolar molecules like oxygen and fat-soluble vitamins slip through the membrane's hydrophobic core easily; charged ions cannot.
Where people slip
Selective permeability is not an all-or-nothing gate — the same membrane can pass one substance freely while blocking another almost entirely.
Your place on the trail
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