Millions,
All life needs water, right? But what about your single celled organisms? Do they need it? If they don’t, what’s the biggest organism that doesn’t need water to survive? Are there any?
Amoeba live in water, and they stay hydrated through osmosis.
Aha!
Do all single celled creatures? (It’s my understanding that amoebas are merely a certain kind of single-celled creature. It’s also my understanding that I remember none of my biology classes)
They all need it; it’s fundamental to the chemistry of life, as we know it (that is to say life, on this planet, as far as we’ve discovered thus far).
Some organisms do well enough without ever imbibing liquid water though; the largest I can think of at the moment would be various kinds of desert rodents, including the gerbil - they can live entirely on the moisture present in their food -bug and plant juice, which of course contains water.
There’s also a state called anyhydrobiosis where organisms (usually dormant seeds) pretty much dry out, but stay alive - except it is more like not dying yet than actual living and in any case, they never dry up completely so as to be completely devoid of H[sub]2[/sub]O - that’s more or less impossible in the natural world, because water is pretty much everywhere to some degree or other.
Anhydrobiosis, not anYhydrobiosis :smack:
Could one argue that viruses are alive & don’t need water? Granted, they thrive only on organisms that need water, but, they themselves don’t necessarily need it. I’m stretching, sure, but we’re learning, right?
They do even better than that. They don’t depend on water present on water in their food, but can actually survive on metabolic water, that is, water produced chemically by metabolizing the carbohydrates in their food.
Can I get that “water produced chemically by metabolizing the carbohydrates” explained a little more? And to think…I used to have no respect for gerbils.
Side note: what other, non-gerbilly animals can do this?
I’ve read that koalas live entirely on the leaves of the eucalyptus tree. I always assumed that meant that they don’t need to drink water, but I could be wrong.
When glucose, for example, is metabolized, the equation is as follows:
C6H1206 [glucose] + 6 O2 = 6 CO2 + 6 H2O + energy
Glucose and oxygen are converted to carbon dioxide and water. Most organisms, including humans, do this. Gerbils are just very efficient at holding on to the metabolic water.
Desert rodents also have extremely efficient kidneys that practically excrete sold urea so little water is wasted on urine.
I read somewhere that gerbils (or some other desert rodents perhaps) construct burrows with a seed store in them; when they take refuge in the burrow, much of the moisture lost by the gerbil’s exhalation is absorbed by the seeds, causing them to start germinating, wherupon they are eaten, reclaiming the water.
I don’t know how true that is…
Many if not most small rodents can do manage it. Even house mice can live on just metabolic water under ideal circumstances, but it’s a knife-edge existence.
As Colibri said all organisms produce metabolic water as a by-product of respiration. The problem with using it as an water source is that respiration generates heat and demands oxygen. As a result when food is broken down the animal’s temperature rises and it breathes more rapidly or deeply. Both of those processes in turn lead to a loss of water. As a result it’s impractical for large animals like people to ever use metabolic water as a water source. We simply lose more water in cooling and breathing than we gained from the digestion. Small animals on the other hand can overcome that because they can have relatively massive nasal pages for absorption of water form the breath as well as ready access to cool, humidified chambers (burrows).
Well it’s debatable is viruses are alive, but they certainly need water. Their only means of reproduction entails lots of water soluble chemicals and they also need an aqueous medium to infect new host cells. That water supply is supplied by the host but the virus is still dependent on being immersed in water in order to reproduce. And there are plenty of actual living organisms that get all their water from their host the same way that viruses do. That doesn’t make them any less dependent on water.
Koalas don’t need to drink standing water, howevere they will occasionally do so. They get their water from the moisture contained in their food, whichis quite a lot, as well as from dew.
I wouldn’t credit it too much. Gerbils are amazingly well constructed to catch most of the water they lose form the lungs before it ever reaches the air. I don’t doubt that the air in the burrow would be somewhat more humid but I doubt it would be enough to promote germination.
Moreover I can’t see such a trait lasting too long. If the seeds were absorbing appreciable quantities of moisture they would be causing a decline in burrow humidity, which would cause the gerbil to lose even more water. And the amount reclaimed by eating the seeds would inevitably be significantly less than the amount lost. The gerbil would be better off digging two burrows, one moist burrow for sleeping and a dry burrow for storage.
Then of course there’s the problem that a germinating seed isn’t really a food store. Germination is something to be avoided as much as possible.