Why is the plasma membrane called a differentially permeable membrane?
GeneralClass 12AllAnswered 27 Mar 2026
Answer
The plasma membrane is termed a differentially permeable (or selectively permeable) membrane because it does not allow all substances to pass through equally. Instead, it selectively permits certain molecules to cross while blocking others based on factors like:
- Size of the molecule
- Chemical nature (water-soluble vs. fat-soluble)
- Charge of the particle
- Concentration gradient
For example, the membrane easily allows small molecules like oxygen and carbon dioxide to pass through, while restricting larger molecules or unwanted substances. This selective nature is essential for maintaining the cell's chemical balance and protecting its internal environment.
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