Question 25

Water molecules enter cells through facilitated diffusion.

Facilitated diffusion is the primary mechanism by which water molecules traverse cell membranes, utilizing specific protein channels that allow for the passive movement of water.

A) Facilitated diffusion

This option is correct because facilitated diffusion involves the movement of water molecules across cell membranes through specialized channels known as aquaporins. This process does not require energy and occurs along the concentration gradient of water, allowing efficient transport into and out of cells.

B) Electrochemical gradients

While electrochemical gradients play a role in the movement of ions and other solutes across membranes, they do not directly facilitate the entry of water molecules. Water transport via electrochemical gradients is not the primary mechanism, making this option incorrect.

C) Gated channels

Gated channels refer to a type of channel that opens or closes in response to specific signals, allowing certain ions or molecules to pass through. Although some gated channels can regulate water flow indirectly, they are not the main transport mechanism for water, which primarily occurs through facilitated diffusion.

D) Proton pumps

Proton pumps actively transport hydrogen ions across membranes to establish a gradient, but they do not facilitate the direct entry of water molecules. This option is incorrect as it pertains to ion transport rather than water movement.

Conclusion

Facilitated diffusion is the correct mechanism for the entry of water into cells due to its reliance on specific channels that enable passive transport. The other options, while relevant to cellular transport processes, do not accurately describe how water molecules enter cells. Therefore, facilitated diffusion stands out as the definitive method for water transport.