How do an engine using hydrocarbons and a body using carbohydrates resemble and differ each other?

In terms of physics and chemistry, how does an engine using hydrocarbons for energy differ and resemble a body using carbohydrates, including waste products?
Lactic acid and carbon monoxide are both the result of using fuel with too little oxygen. While carbon monoxide is chemically simple, lactic acid is a bigger molecule and has many hydrogen molecules sticking to it. Aside from that, how do they differ and resemble each other? How come carbon monoxide doesn’t come with hydrogen tag-alongs?
Please explain this to me like someone whose last chemistry lesson was administered by Walter White.

Lactic acid doesn’t have any hydrogen molecules sticking to it. It contains hydrogen atoms, but so do water, hydrocarbons and carbohydrates. And proteins, and inorganic acids, and bicarbonate, and…

Carbon monoxyde doesn’t have hydrogen because… because if it did, it would be something else. The name itself means “one oxygen and carbon”; or, less literally, “a carbon and an oxygen”, which is exactly its composition. Lactic acid’s name given like that does not mention composition at all: it indicates a property (acid) and where it was isolated first (from milk).

Lactic acid is not produced by combustion, we don’t have little ovens inside. Oxydation, yes; combustion, no.

A livihg body and a combustion machine resemble each other in that both use oxydative reactions to obtain energy in order to perform mechanical work. The dissemble each other in the nature of the reactions: those in the body are much less violent and there are many more of them; also, in the living body some of the energy will be used for mechanical uses (movement, both with respect to its surroundings - walking, flying, swimming - and with respect to itself - pumping blood, breathing…) and some for chemical uses; in a machine, there’s a lot less uses (for a car it’s all about movement, for a heater all about heating).

Not a biologist, but from what I recall human metabolism operates primarily via the Krebs Cycle, which is a series of chemical reactions which enables more energy to be converted into usable form than simple oxydation would, and at far lower temperatures. No artificial engine uses anything like it because of its complexity, it requires either a living organism or something very close to provide the self regulation of chemicals and process stages.

The biggest difference, practically speaking, is that a car engine is a heat engine, and a human (or other animal) body is not. That is to say, a car engine works by first converting all of the chemical energy into heat energy, and then by converting the heat energy into mechanical energy. Conversion of heat energy to any other form is inherently inefficient, with fundamental physical laws limiting how high the efficiency can get, and current car engines are already within shouting distance of that (fairly low) fundamental limit. Animals, by contrast, convert chemical energy directly into mechanical, without using heat as an intermediate, and so we have no such fundamental limits on our efficiency (or rather, if we do, they’re much higher). We’re still not perfectly efficient, but we have room to improve.

Tagging on from Chronos’s post, a curious thought comes to me.

A heat engine is governed by the laws of thermodynamics and at base, the gas laws, which are derived from statistical mechanics. Once you have your heat source, everything is about particles banging against one another, and the fundamental rules are based upon the conservation laws of energy and momentum.

A biological entity is a chemical thing, and the basic laws of how this works are based upon quantum electro-dynamics. It is all about the manner in which electrons and photons interact, especially when they are parts of the complex assemblages we call atoms. All the way from chemical energy sources to the manner in which changes to molecular structures cause mechanical forces to be exerted is governed by the interaction of the constituent electrons as mediated by photons.

So, whilst your heat engine’s physical structure, and maybe heat source, is all about atoms/molecules, the actual manner in which you derive useful work is governed by a totally different set of fundamental laws than a biological entity’s operation.

Eh, all of chemistry, in an organism or out of it, is ultimately governed by QED. But we don’t need to go to that level of detail to explain either combustion of gasoline nor breakdown of glucose and construction of ATP.

2 C[sub]8[/sub]H[sub]18[/sub] + 25 O[sub]2[/sub] --> 16 CO[sub]2[/sub] + 18 H[sub]2[/sub]O
C[sub]6[/sub]H[sub]12[/sub]O[sub]6[/sub] + 9 O[sub]2[/sub] --> 6 CO[sub]2[/sub] + 12 H[sub]2[/sub]O

Some of the waste products are alike … but some are not …

4 Rubber tires ≠ Uric Acid

This isn’t true. We’re much less efficient than engines, and we’re limited by Carnot like anything else. Human muscle efficiency is under 10%. Engines are trivially 30-60%.

I am not a biochemist, but a likely source of inefficiency in biologic processes may likely be mismatch between the energy potential of the driving reaction (such as ATP to ADP+P) and the useful reaction (such as contraction of actin-myosin). I’m guessing that where the imbalance is small, the reaction may proceed relatively slowly but with little energy loss, and that where the imbalance is large, the reaction may be more vigorous but inefficient.

Another place where biologic systems consume energy “inefficiently” is that our processes often require very narrow environmental ranges to work well, so biologic systems often try hard to maintain a constant condition (“homeostasis”). One way to maintain a constant environment is to use a “clamp”, where two opposing biochemical processes occur at the same time. The system adjusts by favoring one process over the other, rather than turning off the un-needed process. It’s like running the heating and the AC simultaneously. Not very efficient, but if set up right, I’ll bet you could control room temperature precisely despite changing ambient conditions.

A better (simpler) example is to imagine how you would hold a pen in a single position in free fall. You could try pushing it with your thumb OR forefinger as needed, but it will bounce back and forth. Pushing with BOTH thumb and forefinger expends energy at rest, but holds it in place better.

I’m not sure how often this kind of “clamping” is used in mechanical systems. I doubt it is used in automotives (but cars are sure a lot smarter than they used to be, so who knows). I would not be surprised if it is used in modern robotics.

No, my point was that a heat engine moving something - once you have heat - needs no QED at all to describe. An organism is QED end to end. Something which is sort of neat (well to me anyway.)

Aeronautics? Particularly flying wings and aerodynamically unstable aircraft like the F-16, perhaps.

Good insight on clamps. I wasn’t familiar with the use of the term that way. Which discipline is it from?

Also, why does a more vigorous result in less efficiency?

I was using the term “clamp” out of context from nerve membrane studies where scientists may “clamp” membrane potentials. It’s been a long time since I’ve read about it, and I don’t remember how it’s done. Other than that, as far as I know, the term lived in my head until now.
The vigorous correlating with less efficiency is a guess on my part, as I said in the post. I’m mentally analogizing with something sliding down an inclined plane.

And when those moving air molecules reach the piston, what causes them to transfer their momentum to it? Electromagnetic forces, and we’re right back at QED. Now, you can describe the process adequately using more primitive theories, but then, that’s true of biochemistry as well. I don’t think there’s anything in biochemistry that can really be understood any better with QED than without it.