Final answer:
Lipids in biology primarily function in long-term energy storage, making up cell membranes, and providing insulation to organisms.
Step-by-step explanation:
The functions of lipids in biological systems are varied and crucial for life processes. Lipids provide long-term energy storage, form the cell membranes that are critical barriers and interfaces for cells, function as insulation materials, and are the building blocks of hormones, in addition to being signaling molecules. In short, the answer to the student's question is:
- b) Make up cell membrane
- c) Long-term energy
- d) Insulation
However, it is important to note that lipids are not commonly used as a source for immediate or short-term energy; this role is typically filled by carbohydrates.