Question: 134: Which type of substance would face difficulty to pass through the cell membrane?
(1) Substance with hydrophobic moiety
(2) Substance with hydrophilic moiety
(3) All substance irrespective of hydrophobic and hydrophilic moiety
(4) Substance soluble in lipids
Answer: Option (2)
Explanation:
The cell membrane is mainly composed of a phospholipid bilayer.
The phospholipid bilayer has hydrophilic heads facing outward and hydrophobic fatty acid tails facing inward.
Due to this structure, the interior of the membrane is hydrophobic in nature.
Substances with hydrophobic moieties or lipid-soluble substances can easily dissolve in the lipid bilayer and pass through the membrane by simple diffusion.
In contrast, substances with hydrophilic moieties are polar or charged and cannot easily pass through the hydrophobic core of the membrane.
Hydrophilic substances generally require specific transport proteins or channels to cross the cell membrane.
Therefore, substances with hydrophilic moieties face difficulty in passing through the cell membrane.