Question

The plasma membrane is impermeable to all molecules except

Answer 1

Ques. The plasma membrane is impermeable to all molecules except *

a) Glucose

b) ATP

c) Urea

d) K+

Answer:

The correct option is c) Urea.

Explanation:

• Urea can pass through the plasma membrane or we can say that the plasma membrane is not impermeable to urea.
• Since urea is a non-polar, uncharged molecule that can combine readily with phospholipids, the plasma membrane is not impervious to it.
• The plasma membrane is selectively permeable and prevents the diffusion of molecules that are charged or polar.
• As a result, all molecules can pass through the plasma membrane but except urea.
• Thus, the correct answer is option c) Urea.

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Answer 2

Answer:

The plasma membrane is impermeable to all molecules except small hydrophobic molecules and gases like oxygen and carbon dioxide

Explanation:

• The plasma membrane is selectively permeable. Hydrophobic and small polar molecules can diffuse through the lipid layer, but ions and large polar molecules cannot.
• The cell membrane acts as a barrier and gatekeeper. They are translucent. That is, some molecules diffuse while others cannot.
• Integral membrane proteins allow ions and large polar molecules to cross the membrane by passive or active transport.

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