* Lipids are essential for forming cell membranes. They are the building blocks of the phospholipid bilayer, which acts as the boundary of all cells, controlling what goes in and out.

* Lipids also have other vital functions:

* Energy storage: Fats and oils are efficient ways for organisms to store energy.

* Hormones and signaling: Steroid hormones like testosterone and estrogen are lipids.

* Insulation: Fats provide thermal insulation, protecting organisms from temperature extremes.

* Protection and cushioning: Lipids help protect organs and tissues.

Therefore, while forming cell membranes is a primary function of lipids, it's not the only one. Lipids play a wide range of roles in biological systems.