Suppose you are studying the transport of a certain polar molecule across the pl

Question

Suppose you are studying the transport of a certain polar molecule across the plasma membrane of cells in culture. Over a period of time, you measure the concentration of a polar molecule inside and outside of the cells. You find that the concentration of the molecule is lower in the cell but is gradually increasing. You also measure the ATP concentration inside the cell and find that it is not changing. Which of the following is probably responsible for the transport of this polar substance into the cell? active transport endocytosis facilitated diffusion secondary active transport simple diffusion Suppose you are studying the transport of a certain polar molecule across the plasma membrane of cells in culture. Over a period of time, you measure the concentration of a polar molecule inside and outside of the cells. You find that the concentration of the molecule is lower in the cell but is gradually increasing. You also measure the ATP concentration inside the cell and find that it is not changing. Which of the following is probably responsible for the transport of this polar substance into the cell? active transport endocytosis facilitated diffusion secondary active transport simple diffusion

Explanation / Answer

c. Facilitated diffusion. Because a mere concentration gradient is not sufficient for the molecule to enter the the cell (high concentration to low concentration) as it is polar. Hence its transport need to be aided/facilitated by specialised membrane proteins.

Not active transport because the movement of molecules is down the gradient. The same is further validated by the fact that the ATP levels donot change

Not endocytosis cause the concentration of the molecule inside the cell is gradually increasing. Had it been endocytosis the concentration of the molecule would increase acutely in one go.

Not secondary active transport because the molecule is moving down the gradient and hence energy need not be spent.

Not simple diffusion because it is a polar molecule and hence cannot cross the hydrophobic lipid bilayer.

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