It's just a guess, but I think it's actually the heating of liquids that reduces oxygen levels, because the solubility rules for gases dissolved in liquids point in that direction. Then if you cool the liquid quickly, the oxygen tends to come back to it, but not as fast, so for some time you'll have a cool liquid with a low oxygen concentration, as if it was hot. And to make the oxygen come back faster, you could stir the liquid or something like that, to increase the surface between it and the surrounding air.
But like I said, I could be wrong. This site says the solubility rules I mentioned apply to water, but not to organic solvents.
Maybe the point of the problem is to find the generic function that relates the two variables. So instead of plotting points for arbitrary values, you could turn your equation into r = kta, where you don't know k, but you do know a, so you know the approximate shape of the graph.
That is my attempt to translate a joke I read in portuguese. Enjoy
So there were two function walking together, f(x)= C and g(x)= ex. They saw a derivative and f ran away, because she didn't want to become 0, but g stayed and said "you can't do anything against me, I'm ex". And the derivative replied "well, looks like you're wrong, because I'm d/dy".
Anyway, I think it's possible that everything that will ever happen was determined from the beginning of the universe, assuming there's no randomness. But no one has control over or even knows what will happen before it happens, so we still get to do what we want. It's just that what we want has already been determined. It's like we're writing an exact copy of a book that has already been written, but has never been read. Now, if we could calculate the future to the slightest detail, I think that would lead to a paradox. Because if, for example, I find out I'm going to lift my left hand 5 seconds from now, I could just not do it, and then I would be changing the predetermined future. But the only way I can change it is if I know it, and the only way I can know it is if it's predetermined and not changeable.
Well, we know that plants don't survive without sunlight. We know that sunlight can act as catalyst for a chemical reaction that produces sugar, which plants need to survive (or something like that), and we know that this reaction does happen within the plants, and every detail about the process. However, one may argue that a superior being wants us to believe in photosynthesis, so he puts all that evidence before our eyes. Or maybe something less fancy. You can say that's ridiculous, but you can't prove that it isn't true, so you live with it.
I don't think it makes sense to worship science, because science is not the laws of physics themselves, it's a description of how we think the universe behaves, based on centuries of observation. Science, as I learned in some class long ago, is one of the 4 ways human try to understand and explain our reality. The other 3 are philosophy, religion, and common sense. With science, we observe facts and then make a hypothesis that would explain these facts, and call it "true" until we find a fact that isn't explained by it, then we find another hypothesis and the process continues.
Richard Feynman made a good analogy with chess, if anyone is interested