In the process of osmosis, can water move directly through the lipid bilayer of a cell membrane?

• A. No, water requires aquaporins to move through the cell membrane.
• B. Yes, water can move directly through the lipid bilayer without any assistance.
• C. No, water cannot move through the cell membrane at all.
• D. Yes, but only when the cell is in a hypertonic solution.

Answer: (A)

Verified step by step guidance

1. Understand the structure of the cell membrane: The cell membrane is primarily composed of a lipid bilayer, which is made up of phospholipids. These phospholipids have hydrophilic (water-attracting) heads and hydrophobic (water-repelling) tails.
2. Recognize the nature of water molecules: Water is a polar molecule, meaning it has a partial positive charge on one side and a partial negative charge on the other. This polarity affects how water interacts with the lipid bilayer.
3. Consider the permeability of the lipid bilayer: The hydrophobic core of the lipid bilayer is generally impermeable to polar molecules, including water, because they cannot easily pass through the nonpolar interior.
4. Identify the role of aquaporins: Aquaporins are specialized protein channels embedded in the cell membrane that facilitate the rapid transport of water molecules across the membrane, bypassing the lipid bilayer's hydrophobic barrier.
5. Evaluate the conditions affecting water movement: While water can move through the lipid bilayer to some extent due to its small size, the presence of aquaporins significantly enhances water permeability, especially under conditions where rapid water movement is necessary, such as in osmosis.