What are some additional roles of lipids?

The correct response highlights some key roles of lipids beyond just their well-known function in cellular structure. Lipids serve as a significant energy reserve for the body. They provide more than twice the energy per gram compared to carbohydrates or proteins, making them an important source of fuel during metabolism.

Additionally, lipids play a crucial role in insulation, helping to maintain body temperature by reducing heat loss. This feature is particularly important in warm-blooded animals. Furthermore, lipids contribute to protection, serving as cushioning for vital organs. For example, adipose tissue acts as a protective layer around organs such as the kidneys, helping to safeguard them against physical damage.

The other options, while relevant in different contexts, do not encompass the broader additional roles of lipids as efficiently. For instance, enzymes for digestion are primarily proteins, while the formation of protective barriers in cells and nutrient transport involve other biological molecules like phospholipids and proteins, respectively.