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Whilst answering this question, an interesting question came to mind.

In the chase through the Hoth asteroid field in The Empire Strikes Back, the Millennium Falcon takes refuge in a cave, which turns out to be the belly of a Space Slug (Wookiepedia tells me that this creatures proper name is an Exogorth).

I never really thought about it before, but how does this creature breathe? Wookiepedia mentions how it gains nourishment

They fed on the minerals of asteroids, various stellar energy fields, mynocks (another silicon-based lifeform), ships, and other unfortunate creatures that unknowingly passed into its mouth.

but school biology teaches me that all living things need to breathe.

Since Wookiepedia is normally pretty good at collating any ridiculous explanation that might have been given in any form of canon and I don't see anything specified, I fear there may be no answer, but I am still curious.

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    Science marches on... I was also taught that Pluto was a planet :D – razethestray Nov 13 '15 at 1:38
  • When I think about that space worm this is all that come to mind – Burgi Nov 13 '15 at 3:22
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    School <insert anything> rarely teaches you about the interesting exceptions, even in what we already know. Breathing is just our way of exploiting the massive amounts of waste oxygen that autotrophes produce - of course it gives us a massive advantage, but it isn't strictly required. The real question is a source of energy - once you have a source of energy and a way to exploit it, you can have life. On Earth, such sources are hard to find apart from organics - but that wasn't always the case. Before cyanobacteria gave us an oxygen atmosphere (which quickly corroded everything) for example. – Luaan Nov 13 '15 at 12:36
  • If they feed on the minerals in the asteroids, then I'd expect their teeth to be more like molars (for grinding) that the pointy-ish things we see in Empire. – Adrian McCarthy Nov 13 '15 at 23:01
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Presumably, they don't need to.

As your excerpt hints at, at the Wookieepedia clarifies, the Exogroth is a silicon-based life form.

All of your biology lessons will have been given based on knowledge of terrestrial, carbon-based life forms. Oxygen is used in our physiology as part of a complex process, which includes the need for a highly electronegative element.

If a similar process is needed in this silicon-based lifeform, then in all likelihood they use a different element or molecule that's found within the asteroids, and process it in such a way that:

  1. Allows them to use it for their respiration-equivalent process (notice the anatomy picture in the wiki includes no lungs, so they breathe different than many Earth animals)
  2. Allows them to store it for long periods of time, as the resource may be hard to find through their limited asteroid-hopping.

However, silicon is a fairly boring element, so far as we know, and doesn't form bonds like our organic chemistry does. In all likelihood, the physiological processes required to sustain such silicon life won't have direct parallels on the microscopic scale.

  • Maybe molten selenium? The main problem that it would have to overcome would be its equivalent of oxygen transport (i.e., blood). Selenium should be okay molten, and it's sufficiently electronegative to get Silicon to agree to play along. (Realistically, Oxygen still would likely serve this purpose, or perhaps Sulfur, but obviously that's out the window.) – Joe Nov 13 '15 at 4:03
  • @Joe My chemistry isn't that good. I could see molten anything being a challenge in vacuum, but substances could theoretically be chemically dissolved into usable molecules. There's apparently a heart system to pump some fluid in a circulatory system. – user31178 Nov 13 '15 at 4:07
  • It's the whole interesting concept of "life as we know it". As Neil deGrasse Tyson likes to point out, if there is non carbon based life out there, we have no idea how it would work, because all of our knowledge is on carbon based life. – Broots Waymb Nov 13 '15 at 15:11
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school biology teaches me that all living things need to breathe.

Yes: all living animals on Earth need to breathe. It's worth noting that even on Earth, some animals breathe in a different way from others (fish take in oxygen from water using their gills, while e.g. mammals and birds take in oxygen from air using their lungs) and some living creatures 'breathe' in different chemicals from others (animals inhale oxygen and exhale carbon dioxide; with plants it's the other way round).

All living beings - animals, plants, and others - that are known to humans live, of course, on Earth. Our knowledge of biology is restricted to those creatures that can survive on this carbon-rich, oxygenated planet. Why on earth would space-dwelling giant slugs need to have respiratory systems even remotely similar to Earth-dwelling creatures?

Wookieepedia also confirms that they can survive in vacuum:

They were silicon-based lifeforms that survived in the vacuum of space by making their homes in the caverns and craters of asteroids.

Silicon-based is already enough to make them sound very different from any Earth beings. The notion of silicon-based lifeforms has been investigated in this article, which says:

Life-forms must also be able to collect, store, and utilize energy from their environment. In carbon-based biota, the basic energy storage compounds are carbohydrates in which the carbon atoms are linked by single bonds into a chain. A carbohydrate is oxidized to release energy (and the waste products water and carbon dioxide) in a series of controlled steps using enzymes. [...]

Wherever astronomers have looked – in meteorites, in comets, in the atmospheres of the giant planets, in the interstellar medium, and in the outer layers of cool stars – they have found molecules of oxidized silicon (silicon dioxide and silicates)

In other words, the necessity of oxygen for living is a property of carbon-based lifeforms, while silicon-based ones might be able to survive based on the silicon traces found in meteorites and by extension asteroids.

  • This official image of the slug's innards doesn't seem to have any lungs or equivalent organisms. – Rogue Jedi Nov 13 '15 at 1:42
  • Great tip about the SW Database! – Hatandboots Nov 13 '15 at 1:44
  • The SW Database seems to be a fan site, so I would be very wary of using it. – Wad Cheber Nov 13 '15 at 1:53
  • @Hatandboots Sorry, I was actually wrong about that; it's NOT more reliable (see Wad's comment above). I hope you were being sarcastic, otherwise I may have led you astray! – Rand al'Thor Nov 13 '15 at 2:01
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    Just a minor nitpick: plants breathe oxygen and release carbon dioxide but plants eat carbon dioxide and poop/piss oxygen. – slebetman Nov 13 '15 at 6:26
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The statement:

all living things need to breathe

is wrong. Even on good old Earth there are lots of organisms that are anaerobic, though admittedly on Earth these are mainly single celled organisms.

Living organisms use a type of chemical reaction called a redox reaction to generate the energy they need to live. In our case we oxidise glucose with oxygen and we need to breate to get the oxygen. However lots of anaerobic organisms oxidise glucose by pathways that don't involve oxygen. The obvious example of this is yeast, as used in beer and bread making, that converts glucose into ethanol. Even yeast still use glucose, but there are extremophile bacteria that metabolise iron compounds.

Now we don't have any canon statements of how exogorths respire, but we know that they are silicon based and we know there are terrestrial organisms that can live on inorganic materials. So it seems entirely plausible that exogorths live by metabolising minerals from the asteroids in which they live. In that case they don't need to breathe at all.

The only problem with this is that anaerobic respiration produces much less energy than oxygen based respiration, which is why only single celled organisms can use it. Maybe exogorths can save up energy and use it all up in a single burst of activity. In that case they'd have to rest for a long time afterwards. I don't know if there is an canon discussion of this aspect of exogorth behaviour.

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school biology teaches me that all living things need to breathe.

If we leave out beings that are theoretical (like silicon based ones, .... . We should maybe think about one thing. What is it that we eat and what is it that we breath in?

Both are in essence the same. Resources that our body needs in order to create the processes that keep us functioning or alive as we call it.

Now if you could take in all these resources just by your food. Do you need to breath? No. Furthermore this also means if you had that ability then the need to breath is not there and thus evolution probably would see to you loosing your lungs and getting something more useful in its place.

Thus if we keep that in mind it is possible that there are life forms that have no need to breath at all and also such a space slug is possible there (although what keeps me worrying more than them breathing is how they travel from asteroid belt to asteroid beld.....sublight that is).

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