Which is one function of steroids?
waterproofing leaves and feathers
insulating and protecting bones and organs
serving as chemical messengers
providing energy storage

The most appropriate answer here is serving as chemical messengers.

Explanation:

Steroids are actually lipids which are insoluble in water i.e. hydrophobic in nature. Most common steroid is cholesterol. Cholesterol helps in stabilizing the plasma membrane.  Cholesterol also serves as precursor of Vitamin D and many other hormones like Aldosterone, cortisol, estrogen and testosterone. These steroid hormones act as chemical messengers. Since these hormones are hydrophobic, they can directly pass through the plasma membrane and nuclear membrane and act directly on the DNA.

thermophiles, notice the prefix thermo.

life would be meaningless without memes