Question

1. describe why hydrophobic molecules can easily pass through the cell membrane but hydrophilic molecules can’t.

Explanation:

The cell membrane has a phospholipid bilayer structure. The phospholipids have hydrophilic (water - attracting) heads and hydrophobic (water - repelling) tails. The interior of the bilayer is made up of the hydrophobic tails. Hydrophobic molecules are non - polar, and they can interact favorably with the hydrophobic interior of the cell membrane, so they can easily pass through. Hydrophilic molecules are polar or have a charge. They are repelled by the hydrophobic interior of the membrane. Also, the hydrophilic heads face the aqueous environments inside and outside the cell, but the hydrophobic core acts as a barrier for hydrophilic substances. For a hydrophilic molecule to pass through, it usually needs specific transport proteins (like channel proteins or carrier proteins) to facilitate its movement, while hydrophobic molecules can diffuse through the lipid bilayer directly.

Answer:

Hydrophobic molecules can pass through the cell membrane easily because the cell membrane's phospholipid bilayer has a hydrophobic interior (composed of phospholipid tails). Hydrophobic molecules, being non - polar, can interact favorably with this hydrophobic region and diffuse through. Hydrophilic molecules are polar or charged. They are repelled by the hydrophobic interior of the membrane. Also, the hydrophilic heads of phospholipids face the aqueous environments (inside and outside the cell), but the hydrophobic core blocks the direct passage of hydrophilic molecules. Hydrophilic molecules typically require transport proteins (e.g., channel or carrier proteins) to cross the membrane, while hydrophobic molecules can diffuse through the lipid bilayer directly.