Which phrase best describes the property of selective permeability in biological membranes?

• A. Prevents any substances from crossing the membrane
• B. Allows some substances to pass through while blocking others
• C. Allows only water molecules to pass through
• D. Permits all molecules to move freely across the membrane

Answer: (B)

Verified step by step guidance

1. Selective permeability is a fundamental property of biological membranes, such as the plasma membrane, which regulates the movement of substances in and out of the cell.
2. Biological membranes are composed of a phospholipid bilayer with embedded proteins. The hydrophobic core of the bilayer prevents certain molecules, such as ions and polar molecules, from freely crossing the membrane.
3. Selective permeability allows the membrane to control the passage of substances based on factors like size, charge, and polarity. For example, small nonpolar molecules like oxygen and carbon dioxide can diffuse freely, while larger or charged molecules require specific transport mechanisms.
4. Transport proteins embedded in the membrane facilitate the movement of certain molecules. These proteins include channels and carriers that allow selective passage of substances, ensuring the cell maintains homeostasis.
5. The phrase 'Allows some substances to pass through while blocking others' best describes selective permeability, as it highlights the membrane's ability to discriminate between different types of molecules based on their properties.