Final answer:
The membrane allows gases to pass through but not soluble particles or molecules due to its selective permeability, allowing only nonpolar and small molecules to diffuse easily. Ions and polar molecules require transport proteins to move across the membrane.
Step-by-step explanation:
This membrane allows gases to pass through but not soluble particles or molecules. The rationale behind this is based on the properties of different molecules with respect to the membrane's structure. Membranes range in thickness from 6 to 9 nm and are flexible and fluid. They are known to be freely permeable to water and some gases due to their small size and nonpolarity.
However, membranes are impermeable to electrically charged ions like Na+, Cl¯, or H*. These ions, as well as other charged particles, cannot diffuse through the hydrophobic interior of the membrane due to their charge. Similarly, polar but uncharged molecules like sugars also cannot easily pass through the lipid membrane. Such impermeable substances are typically transported with the help of membrane transport proteins. Lipid soluble molecules, on the other hand, can readily pass through.
Transport proteins play a crucial role in the movement of ions and polar molecules. Channel proteins, gated channel proteins, and carrier proteins are examples of transport proteins that facilitate diffusion across the membrane for substances that cannot freely do so.