Answer
Some substances are able to pass through the plasma membrane bi-layer without the aid of transporter proteins. Some classes of substances that can enter or leave cells by simple diffusion are (a) non-polar molecules like oxygen, (b) hydrophobic molecules like fatty acids, and (c) small, uncharged polar molecules like urea.
Work Step by Step
Some substances that pass in and out of cells by simple diffusion are:
Non-polar and hydrophobic molecules, such as carbon dioxide, nitrogen, testosterone, and Vitamin A; and
Small uncharged polar molecules, such as water, urea, and small alcohols.
