Question

Which of the following boundaries do the molecules have to cross during short distance transport?

• A. Cell wall
• B. Cell membrane
• C. Plasma membrane
• D. All of the above.

Answer 1

The correct option is D All of the above.

During short distance transport (SDT) the molecules have to cross 2 boundaries- cell wall and cell membrane (plasma membrane). Cell wall is freely permeable to all substances. Cell membrane is selectively permeable. Small non polar molecules (oxygen, nitrogen, carbondioxide) can easily pass through the cell membrane. Uncharged polar molecules- small (water, ammonia, glycerol) and large (glucose, sucrose) can partially pass through the cell membrane. Ions (${\mathrm{Na}}^{+}$, $K^{+}$, ${\mathrm{Cl}}^{-}$ etc) cannot easily pass through the cell membrane. The cell membrane is freely permeable to water.