Since Notothenioid fish do not have glomeruli in their kidneys, the antifreeze glycoprotein are never expelled into the wastes from the blood so no energy needs to be used to reabsorb these glycoproteins. Your students might be able to come up with more examples as they go through this suite of activities. Every reaction is regulated by an enzyme which is a specialized protein that acts as a catalyst. This is thrifty because it decreases the amount of energy that the organism needs and it protects the organism against the excessive heat that would have to be used if enzymes were not present. Each enzyme can be used over and over since it is not changed by the reaction it regulates.
Most enzymes work best at the temperature typical for the organism in which it occurs.
At higher temperatures there is more molecular motion so the enzyme can collide with the substrate molecules more often and cause more reactions to happen. This causes the rate of chemical reaction to increase. At lower temperatures there is less molecular motion so there are less enzyme-substrate collisions so the chemical reaction rate decreases. Because of this, any cell activity will also decrease at colder temperatures. This would explain why the highest temperature in the enzyme activity may have had no reactions occurring.