What are lipids primarily used for in biological organisms?

Lipids serve crucial roles in biological organisms, particularly in energy storage and forming cellular structures. The hydrophobic nature of lipids allows them to form membranes, such as the phospholipid bilayer that constitutes cell membranes. This structure is essential for maintaining cellular integrity and creating compartments within cells, facilitating different biochemical processes.

In addition to their structural functions, lipids are a major source of energy. They provide more than double the energy per gram compared to carbohydrates and proteins, making them an efficient form of energy storage. When energy is needed, organisms can break down these stored lipids to release energy.

While some other options hint at important biological functions, they do not capture the primary roles of lipids as accurately. For instance, transporting nutrients is mainly the role of proteins and certain carbohydrates. DNA storage is specific to nucleic acids, while catalyzing reactions predominantly involves enzymes (which are proteins). Hence, the primary functions of lipids are best captured by the energy storage and structural roles they play in cellular biology.