Final answer:
The small diameter of the tunnel in a semipermeable membrane specifically permits the passage of small molecules and not large molecules or ions, which may require facilitated diffusion or ion channels to move across the cell membrane. correct answer is option B.
Step-by-step explanation:
Based on the provided information, the small diameter of the tunnel in a semipermeable membrane allows the passage of small molecules. Large molecules, charged ions, and polar substances typically have difficulty passing through the plasma membrane without assistance because they cannot diffuse through the hydrophobic interior of the membrane. Similarly, the concept of size exclusion in ion channels indicates that the size of the pore is specific and, therefore, excludes larger ions or those not matching the charge requirements of the channel.
Facilitated diffusion is a process that helps transfer molecules like glucose and amino acids across the membrane by using specific protein channels, thus allowing them to move down their concentration gradient without requiring energy. Ionic molecules such as sodium (Na+), potassium (K+), and calcium (Ca2+) can pass through the membrane via ion channels that are selective for charge but not necessarily for size, or through facilitated transport via carrier proteins or channels.