To be an effective solvent in living systems, a substance must be able to meet all but one of the following requirements, namely a) remains liquid over a wide temperature range. b) form a solution with lipid molecules. c) able to dissolve a great variety of chemical compounds. d) provide a safety against extremes in temperature by having a high heat capacity.

B. form a solution with lipid molecules.

Explanation:

To be an effective solvent in living systems, a substance must be able to all BUT one of the following. That is form a solution with lipid molecules. Because water does not combine readily with lipids, lipids are able to form barriers, like cell membranes, within the living system called the cell.

i believe it is "they are not used up by reactions" as the answer to your question, text me back if this is correct because i just learned this.