Energy, Heat, ATP
Most recent answer: 01/26/2016
- Judy (age 68)
Atlanta, Ga, USA
Great questions. Your confusion about whether heat is a type of energy transfer or a form of energy means that you've been listening carefully enough to know that the word is used in at least two different ways, not consistently. When we're being very careful, we say that heat is energy transferred due to temperature differences. The amount of energy that an object has due to not being at absolute zero temperature is called "the amount of thermal energy". In sloppier speech we often use "heat" in pace of "thermal energy". The reason that can lead to confusion is that thermal energy can get into something via other ways than heat flow. You metion a good example- the heating of a gas by the work done compressing it. So an object has a well-defined amount of thermal energy in it, but not a well-defined amount of heat in the careful sense of the word.
Brownian motion is something that particles that have some thermal energy in a fluid do as they move around, bouncing off other particles. That type of motion is only one of the forms of thermal energy. I don't know what it would mean to say that Brownian motion "caused" thermal energy or vice versa. It's a little like asking whether trees cause forests or vice versa.
On how ATP drives little engines, e.g. those ion pumps, people do know, but not us! I'll try to get an answer from a biophysicist colleague and then update this. Now that you've raised the issue, one of the most interesting questions is how many altogether different evolutionary paths there were for those ATP engines (linear muscle movements, circular rotors, ion pumps,...) and how many branched of from a smaller number of different early versions. Meanwile, here's a Wikipedia article (https://en.wikipedia.org/wiki/Na%2B/K%2B-ATPase) that discusses the ATP-driven ion pump, but without a nice picture of the comparative free energies of the various intermediate states.
Mike W.
(published on 01/26/2016)