Lipid-soluble materials enter and exit the cell via simple diffusion across the cell membrane.

Here's why:

* Cell membrane structure: The cell membrane is primarily composed of a phospholipid bilayer. This bilayer has a hydrophobic (water-repelling) interior and hydrophilic (water-attracting) exterior.

* Lipid solubility: Lipid-soluble molecules, like steroids, fatty acids, and some vitamins, are able to dissolve in the hydrophobic interior of the membrane.

* Simple diffusion: This process does not require any energy or assistance from membrane proteins. Lipid-soluble molecules simply move down their concentration gradient, from an area of high concentration to an area of low concentration, across the membrane.

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