My husband and I *love* to walk ...for hours and hours, and if we decide to go ahead with this potential trip - I'm going to need good shoes. These days, I have some reasonably good shoes for the most part - but they are 2-3 hour walking shoes, not necessarily good for 6+ hours of tromping around.
In cell biology, selective permeability is the property of a living cell membrane that allows the cell to control which molecules can pass through the membrane, moving into or out of the cell.
Membranes can be classified as impermeable, permeable, semipermeable or selectively permeable. An impermeable membrane is one through which no substance can pass. Semipermeable membranes are those which only let solvents, such as water, pass through them.