11
$\begingroup$

Background

Some species are homeotherm (internal temperature is not affected by a change in external temperature) and some are poikilotherm (internal temperature changes in response to external temperature). These concepts apply to individual levels.

How about cells (unicellular cells as well as cell in a multicellular organism)? I know that cells react to temperature change. For example, the amount of cholesterol in the cell membrane can vary in response to temperature in order to keep a membrane fluidity roughly constant (ref). But that doesn't prevent the internal temperature to change.

Question

When the external temperature of cell changes, does it affect the internal temperature? I am hoping that the process is general enough so that I don't have to specify a particular organism. If it is needed to talk about a particular organism, then consider a yeast for example. How does the internal temperature of a yeast vary with a change in the external temperature?

EDIT

My knowledge in Physics being very limited, I didn't even think of Fourier's law before reading @Eli Korvigo's answer and comment and @AMR's comment. So let's make some calculations:

If we consider a spherical cell of area $4\pi r^2$, where $r$ is the radius, then the loss of heat is $4\pi r^2 \cdot \Delta T \cdot K$ (Fourier's law), where $\Delta T$ is the temperature differential and $K$ is the thermal conductivity. Then the ratio of heat production $H$ over the thermal conductivity $K$ (in order to deal with this change of $\Delta T$ °C) is $\frac{H}{K} = 4 \pi r^2 \Delta T$. If $r = 10^{-6}$ meters and $\Delta T = 2$ °C, then $\frac{H}{K} ≈ 10^{-11}$. Am I right?

Is this ratio really not realistic for a cell? The thermal conductivity for water is $k=0.56 \frac{W}{m\cdot K}$(ref.) and the heat production per cell is $34 \cdot 10^{-12}$ W (ref.). So the ratio is of the order of $10^{-11}$ as well! Am I right?

So is it really impossible for a cell to regulate its temperature?

$\endgroup$
  • $\begingroup$ When you do cell/tissue culture, you learn to work fast so that you do not keep your cultures out of the incubator for very long. You make sure it is set for 37* and that your CO2 take is not on empty. In short cells are adapted to the environment they evolved in. Mammal cells do not respond well to dry, too cold or too hot environment and oxygen and about 5% CO2 to culture. Bacteria are pretty sturdy and have a broader range where they can survive, but they generally won't grow outside oh their ideal range. For E.coli, against that is 37* as they evolved in mammalian digestive tract. $\endgroup$ – AMR Aug 23 '15 at 22:08
  • $\begingroup$ Think about it this way. You reach a few hundred meters from the summit of The Matterhorn as night falls in January. You can sleep exposed, in a tent, or in a tent in a cocoon sleeping bag, or in a tent with sleeping bag and a few climbing partners. Option 1, you will probably be severely hypothermic in the morning or possibly dead. Option 2 you probably won't be much better off. Option 3 you should be okay, though you may be apprehensive about unzipping the bag in the morning. Option 4 the temperature of the tent will likely also be warmer than the ambient temperature outside. $\endgroup$ – AMR Aug 23 '15 at 22:18
  • $\begingroup$ I understand that cells (unicellular or not) have their ecological niche. But it is not because you have such niche that you won't evolve so to regulate your inside temperature in order to expand over this niche (as mammals do for example). So I think the question remains (Are cells (yeast for example) able to regulate their inside temperature). $\endgroup$ – Remi.b Aug 23 '15 at 22:22
  • $\begingroup$ I would say that there is a range of response to the environmental change that the cell experiences, but no individual cell has the capacity to regulate temperature. They can respond to the change, but you need systems to actually control temperature. Multicellular organisms are greater than the sum of their parts, so even though systemically we (warm-blooded animals) can make modifications to metabolic activity that regulates out core temperature, it is the result of the collective response more than that of any individual cell. $\endgroup$ – AMR Aug 24 '15 at 0:33
  • $\begingroup$ And that is just considering Mammals. There are some very large reptiles who are not capable of maintaining their body temperature, even though they have the critical mass to do so. Their response to cold is hibernation, or in the case of the really large ones, dinosaurs, extinction. $\endgroup$ – AMR Aug 24 '15 at 0:38
8
$\begingroup$

Homeothermic multicellular organisms have special tissues that burn resources to warm up (usually this involves breaking the electron-transporting chain at the final stages of respiration to transform all chemical energy into thermal energy). And they have special tissues (fat) and enough body mass (this is more about the volume/area ratio) to keep this energy from dissipating. If you recall physics, any unicellular organism has insufficient body mass to accumulate thermal energy for any perceptible amount of time, hence it's useless to burn resources that it can spend to adapt to lower temperatures, i.e. synthesise cold-shock proteins, modify membranes, restructure metabolism. This is basically the same reason why small mammals and birds have to eat all the time to stay alive.

enter image description here

As you can see, the smaller you get the more energy you need to burn (hence increase ${O}_{2}$ consumption) to maintain body temperature. That's why we don't see truly homeothermic insects (some of them can warm up for short periods of time) or other small animals.

$\endgroup$
  • $\begingroup$ Thnks for your answer +1 You said any unicellular organism has insufficient body mass to accumulate thermal energy for any perceptible amount of time, hence it's useless to burn resources that it can spend to adapt to lower temperatures That means that there is absolutely no control over internal temperature at the cellular level in comparison to the extra-cellular temperature. Is that right? That'd be great if you'd have a reference. $\endgroup$ – Remi.b Aug 23 '15 at 19:13
  • $\begingroup$ @Remi.b I don't mean this is impossible, but thermodynamically irrational. This statement directly follows from the Fourier's law. A cell is simply too small, hence any energy spent to warm up will dissipate immediately. Don't forget about the energetic capacity of water. $\endgroup$ – Eli Korvigo Aug 23 '15 at 19:34
  • $\begingroup$ Eli's answer makes sense, but here is an example. If you put a substantial mass of yeast in a cask with crushed grapes or wort, they will initiate fermentation to produce alcohol for beer or wine. If you look at a temperature, the temperature within the vat will be higher than the ambient temperature. With enough mass, the yeast produce enough heat to warm the container that they are in. However a culture on a petrie dish would likely generate insufficient heat to overcome the effects of the ambient temperature of the surroundings. $\endgroup$ – AMR Aug 23 '15 at 19:53
  • $\begingroup$ Thanks a lot for the comments as well. I plugged a few numbers into Fourrier's law to see if it is plausible for a cell to regulate its temperature (See edit). Please let me know if that sounds correct to you and whether you still think it is impossible for a cell to regulate its own temperature. $\endgroup$ – Remi.b Aug 23 '15 at 21:06
  • 1
    $\begingroup$ @Remi.b there are two possible flaws in your estimations (I can be wrong, since I don't have time for a thorough analysis right now): 1. You applied a 1D approximation to a 3D case; 2. you reference heat production per cell in a culture during growth (=> a lot of spare resources to burn) - the value is not relevant to an isolated cell (and that is the model we are talking about as far as I believe). As you might've noticed Over an 8.5 h period, cell numbers increased by 9% and heat production per cell by 18% - the heat production per cell correlates with the number of cells. $\endgroup$ – Eli Korvigo Aug 23 '15 at 23:10

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service, privacy policy and cookie policy

Not the answer you're looking for? Browse other questions tagged or ask your own question.