Which of the following is a characteristic of lipids?

Lipids are a diverse group of organic compounds that share a common characteristic of being hydrophobic or non-polar, which means they do not dissolve in water. This property makes them essential for various biological functions, including serving as structural components of cell membranes.

The primary role of lipids in cell membranes is to form a phospholipid bilayer, which provides a barrier that separates the interior of the cell from the external environment. This bilayer is crucial for maintaining cell integrity, creating compartments for different cellular functions, and facilitating the controlled movement of substances in and out of the cell. In addition to structural roles, certain lipids play important roles in signaling and energy storage.

The other characteristics mentioned do not accurately describe lipids. They are not soluble in water, and they are not made up of amino acids or polypeptides, as those are characteristics associated with proteins, not lipids. Thus, the role of lipids as structural components of cell membranes is a fundamental aspect of their biochemistry and cellular function.