Jimmy Hopkins (yes, that's his name) is a extremely weird organism. For one thing he is extremely large, but on the other hand, he is extremely weird, because of one thing- He is an unicellular organism

You heard it right. JH is just nothing but a giant unicellular organism about 50m across and 30m tall, resembling a giant bacterium. JH has a extremely hard capsule made of cellulose and lignin, to protect it from abrasions and dents. Inside JH is a collection of thousands of chloroplasts to produce food. JH's mitochondria are really nothing more than a bunch of oversized mitochondria that produce a lot of energy. Since JH is so massive, it would die if it were to exist on land, so it simply swims in the ocean. JH has multiple flagella that are about twice as long as the host organism itself, which help it to propel through at high speeds through the water. In short, JH is basically an upscaled version of an cyanobacteria, except with chloroplasts and a proper nucleus. JH is rod shaped. Sorta like this:-enter image description here

However, JH's size and unique shape makes it an tempting target for creatures, which means that JH has multiple predators. So JH needs to have a energy source that can provide sufficient energy for escaping.

The problem is, if JH were to use ordinary glucose for energy, then it would have to use so much glucose that the sheer weight would offset the amount of energy to propel it, meaning that JH would move sluggishly. JH needs to move extremely fast, literally plowing itself through the water. JH cannot produce short bursts of energy, i.e. reach high speeds for just a few seconds like a cheetah and slow down. JH needs to be moving at breakneck speeds for at least a few minutes to escape its predators. So JH would need a more energy-dense substance to propel itself, without just exhausting its energy supply.

Initially I was thinking that JH would use nuclear reactions to propel itself forward at these speeds, but I am no longer optimistic about this due to the reasons below:

  • There is a reason why cheetahs don't use fission reactors to propel themselves. Nuclear fuel is overkill. If JH were to use uranium/plutonium for propulsion, then it would self-destruct due to the sheer amount of radiation being released which would cause it to disintegrate.
  • Nuclear energy is non-rechargeable i.e. you can renew your glucose supply by making glucose, for e.g. but you cannot make "uranium" to replenish its energy supply, you would need a supernova to make uranium, not just the meagre energy of a cell.
  • Nuclear Fusion- Do I need to explain myself?

So, although JH is still using the glucose from its chloroplasts for metabolic purposes like maintaining cell temperature and peacefully swimming, it needs a emergency fuel, one that is much more energy-dense than glucose, which it can use during crisis mode, i.e. when it is under threat from predators or escaping a natural disaster, so that it can flee the area.

The final question is:

What kind of energy-dense fuel would JH use in order to flee at high speeds without getting exhausted quickly?


  • The fuel should be something that has a much higher energy density than glucose, i.e. that a certain amount of the fuel would produce more amount of energy than a similar amount of glucose.
  • No nuclear fission or fusion, please.
  • Something that can be easily replenished by JH.

EDIT: Some clarifications:-

  • JH does not photosynthesize in the deep ocean. It instead comes up to the surface for brief periods of time to produce food.
  • JH is rod-shaped, not spherical
  • JH uses the oxygen that it gains from the photosynthesis for metabolism
  • JH is not hostile to symbiotes. In fact, it is extremely calm and passive towards animals such as anemones and friendly fungi, which protect JH from predators (in case of fuel depleteion), in return for oxygen and glucose that JH synthesizes, and enhanced mobility. So JH can allow them to "roost" on the surface of JH. JH is only hostile towards predators and enemies.
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    $\begingroup$ Glucose is an energy storage and transport medium. It's only an energy source when it is acquired from some other organism that stored energy as glucose. If JH is expending quantities of energy that can not be stored within its bulk as glucose, where is it coming from? Not from chloroplasts...large photosynthetic organisms are typically sessile for good reason. $\endgroup$ Commented Oct 26, 2022 at 18:11
  • $\begingroup$ Additionally, if it's expending more energy than its body can store as glucose over the course of a few minutes, how is it not cooking itself? $\endgroup$ Commented Oct 26, 2022 at 18:12
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    $\begingroup$ Fatty acid(vegetable oils/ blubber/fat etc) have approximately similar energy density to kerosene, coal etc. Going above this means increasingly likely to be unstable compounds. As in highly reactive, explosive etc. $\endgroup$ Commented Oct 26, 2022 at 18:24
  • $\begingroup$ Why do you need a new energy source. Why can't he just use whatever normal single celled organisms use? $\endgroup$
    – Daron
    Commented Oct 26, 2022 at 19:45
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    $\begingroup$ JH having mitochondria is pointless, it can't exchange oxygen fast enough to make use of oxygen metabolism for anything BUT short bursts. JH has virtually no surface area compared to its volume. This is the main reason cell size is limited. $\endgroup$
    – John
    Commented Oct 26, 2022 at 19:49

6 Answers 6


The problem is, if JH were to use ordinary glucose for energy, then it would have to use so much glucose that the sheer weight would offset the amount of energy to propel it, meaning that JH would move sluggishly

Then what you're looking for are energy density and reaction speed. You need something that'll react quickly, releasing a lot of energy.

Explosives fulfill the second condition, not much the first. Now, to satisfy the first condition we have to fiddle with molecular structure, which is hard (you cannot squeeze all that energy into a chemical compound). The second is much easier to circumvent preparing the reaction and using the appropriate catalysts (sugar and flour, if finely powdered, can react fast enough as to cause explosions).

For example: graphite (solid monocarbon) has an energy density three times that of sugar (which is about three to four times that of most explosives), but it can't react without oxygen, and how are you supplying enough oxigen to a graphite core? Can't extract it from water fast enough, can't store it efficiently into an organism.

Assuming we can ignore toxicity, the best compromise is 2:3 aluminum copper oxide sludge. Energy density about sixteen million joules per cubic decimeter (about the same as octanitrocubane explosive, twice that of nitroglycerin). It carries its own oxygen, all the energy comes from the swapping of molecular bonds between the metallic aluminum and the copper atom.

Now it's all a matter of efficiency, because if even a small part of that energy is released as heat, your single-celled behemoth is going to cook from the inside, whatever the fuel. Uncontrolled ACO reaction can reach a temperature of 2500 Celsius degrees in air. Being inside an aqueous single-cell organism there's a physical limit of 100 °C, but chloroplasts will die at about 48 °C, and most biochemical reactions go awry beyond 50 °C (unless you've got a thermophile organism, but that comes with its own compromises).

Speaking of efficiency, you want to minimise drag and section to achieve higher speeds and longer endurance. Jimmy ought to be able to compress itself into a sort of eel-like shape to escape, maybe using its own body as a propeller, moving in a fish-like way.

Another escape possibility could be an old lizard trick - abandon some flagelli behind, to act as a distraction.

Also, being monocellular doesn't prevent your beastie from having cnidocysts on those flagelli - or everywhere on its surface for that matter. And at that point, the right poison will turn Jim from everyone's favourite meal to something everyone's actively endeavours to avoid at all costs.

  • $\begingroup$ And how would you find ACO naturally? $\endgroup$
    – Alastor
    Commented Oct 31, 2022 at 17:37
  • $\begingroup$ @FuriousArcturus "naturally" -- you don't. You need a biological mechanism that will select, accumulate and keep aluminum and copper oxide. Both can be found in water, in minuscule quantities. Earth seawater supplies about 1ppb of Al and about 1/10 that in copper, i.e. you need to filter one billion liters of water to get one kilogram of copper. A 100% efficient, ten litre sponge would take about 130 years to do that (a hundred-litre sponge, 13 years, and so on). Once you do, however, you can reuse them, provided you have a "recharge" mechanism to refine aluminum and safely oxidize copper. $\endgroup$
    – LSerni
    Commented Oct 31, 2022 at 22:23

So. Many. Problems.

So much so the only viable solution is:


Why magic.

  • Flagellum function well at microscopic, not so much at macroscopic. Scaling up a flagellum by a factor beyond 1000 is just not possible without some major redesign. So never mind the energy source, whats the propulsion?

  • If moving by body motion. How is it moving its body? It has no muscle tissue. normal unicellular creatures use affects that don't operate at macro scale.

  • A sphere of 30m diameter is approximately 700 tonnes of mass. More then a blue whale. This mass makes moving at high speeds thorough the high friction environment very difficult in terms of energy and means of propulsion.

  • How is energy being gathered in the first place? Beyond a some cm of depth within the organism photosynthesis is effectively useless.

  • Too large for a single nucleus. Multi nucleus per cell does happen and would have to happen for this creature to function This feeds into the communication problem.

  • Communications. If one side of Jimmy is being nibbled. How long before the other side knows. If one side is fleeing while the other is not that will be a problem. Jimmy could end up with one side wanting to flee west and the other to flee east. Which would spin Jimmy like a top or pull Jimmy into two.

  • Gas diffusion is a huge issue. Circulatory systems exist for a reason. Creatures without Circulatory systems are very limited in size. Long spindly body forms can compensate for lack of circulatory system.

  • Huge bursts of metabolic activity mean large increases of temperature. Without a circulatory system, or some other tricks, cooked insides us very likely.

  • Without multicellular tech the ability to have specialized organs/organelles is much harder. Systems to handle high energy fed to a large propulsion system normally has dedicated hardware.

  • How much nibbling should be tolerated before extreme flee is activated? Too much and Jim is dead. Too little and Jim is vulnerable to the next nibbler.

  • Sudden accelerations will put strain on a unicellular organism, how will it avoid being shredded by its own escape mechanism?

  • Fast movement is not defense against infections. Jim has minimal defense against bacterial or fungal infection.

  • What is preventing fleeing onto shore, into sharp rocks etc?

Problems with transport.

The limitations to creatures moving really fast is more often limitation of thermal dissipation and getting fuel in and waste out. If you 'feel the burn' that is an issue of not getting enough fuel in quick enough. That is, in my opinion the fuel is not the problem.

This will be a huge problem for a unicellular organism. Say it did have a pocket rich in fatty acids and glucose. If that is used that to power its propulsion system. How is the carbon dioxide disposed of? How will it get fresh fuel? How did it get oxygen in there? How will it dispose of the heat? temperatures in excess of 40c over many cubic meters will take a while to dissipate even while in a water environment.

That is to say how Jimmy gets ANY energy source in place is bigger issue then better energy source.


Using magic and or narrativium all these problems go away, it just works.

Alternatively you will have to create a rule set for your universe that has different physics that will allow Jimmy Hopkins to be plausible.


In the book The Legacy of Heorot The antagonist creature would use a a gland in its body to release super oxygenated blood into its circulatory system. Doing what Nitrous Oxide does to a combustion engine. The downside was that all the heat generated by the activity would overheat the creature an could only do so for short periods of time. And could never be far from water.

Perhaps not being a long term source for energy, a hydrogen peroxide like producing gland would give your creature the extra boost it needs by more efficiently burning the fuel it already uses. Ie: Instead of a different source, an additive to more efficiently use what it has.

The downside, the process does produce prodigious amounts of heat, but being a water living creature this is ok, as long as it does not strey into very warm tropical waters.

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    $\begingroup$ And it'll be hungry afterwards. But that just enhances the story! $\endgroup$
    – JBH
    Commented Oct 26, 2022 at 21:56

Learn to squeeze yourself

Sugar isn't the problem, it's extremely energy dense. The problem is your shape is terrible for swimming through water.

Bacteria can squeeze themselves into small spaces so Jimmy Hopkins can do the same. Squeeze yourself into a streamlined shape that doesn't need to displace a massive amount of water and you can massively increase your speed and reduce the energy needed to move. This also allows you to dodge attacks by rapidly changing your shape in unpredictable ways.


Nitrated sugars

A lot of people don't realise that well over half of our most commonly used explosives are just nitrated organic compounds.

Nitroglycerine = nitrated glycerine. TNT = nitrated toluene. Guncotton = nitrated cellulose Etc.

You can pretty much pick your reactive molecule and biologically nitrate it. Sugar nitrates are easy to make, and fairly stable unless you purify them or catalyse their breakdown.

Now, JH may have reservations about being filled with what is very much like nitroglycerine. What giant, self aware bacterium or amoeba wouldn't? But he need not worry. There are plenty of ways he can use it:

  1. Store and then metabolise it at low concentration relatively normally using some amazing enzyme that captures almost all the energy.
  2. Concentrate it a bit and let it deflagrate, generating heat for some sort of jet pump, or a gas jet, or to thermally activate some sort of high-T super fast glucose metabolism, eating through his stores in seconds.
  3. Metabolise it however you like but swim upwards. Don't release the gases. Retain them, swelling his carapace, displacing water, resulting in huge upwards force.
  4. Really concentrate a water insoluble species. Poop it out. Release a catalysing enzyme. Smile,you son of a paramecium! KABOOM! Weren't expecting that from a monocellular lifeform, were you, Jaws?
  • $\begingroup$ Combine this with @Gillgamesh's excellent answer for best effect. $\endgroup$
    – user86462
    Commented Oct 27, 2022 at 6:00
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    $\begingroup$ Sugar is 4 times more energy dense than TNT, so this doesn't really solve the issue. $\endgroup$
    – Nepene Nep
    Commented Oct 27, 2022 at 10:35
  • $\begingroup$ Being filled with TNT would explain why predators avoid eating it. $\endgroup$
    – PTwr
    Commented Oct 27, 2022 at 11:10
  • $\begingroup$ @NepeneNep Justify that x4? TNT has higher enthalpy of combustion, similar density and molar mass. And provides its own oxygen (not trivial) for metabolism, and is probably the worst case here anyway. Nitrated sugar must obviously be an improvement on sugar. $\endgroup$
    – user86462
    Commented Oct 27, 2022 at 18:15
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    $\begingroup$ newscientist.com/article/… basic science. And sugar is pretty easy to explode if you powder it. $\endgroup$
    – Nepene Nep
    Commented Oct 27, 2022 at 22:36

Pressurized water.

JH is big. Within JH is an elastic organ that it pumps full of water. THis organ is also big and holds a lot of water. This accumulation and pressurization is gradual and done with standard biologic mechanisms.

The water is under pressure and the pressurized water is the storage medium for energy. To escape, JH releases the pressure and uses the water as jet propulsion.

As a bonus, the water in the pressure organ is not just water. JH synthesizes and accumulates certain additives which are also in the water. When the water comes jetting out, it is generally in the direction of a predator and would-be pursuer. The additives in the water cause would-be pursuers to become discouraged, and inclined to move in another direction.

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    $\begingroup$ Umm an organ in a unicellular organism? that would be an organelle you mean wouldn't it? [Wanders away to check] .. [wanders back] yup, think you meant that rather than organ dude 🤗 $\endgroup$
    – Pelinore
    Commented Oct 26, 2022 at 18:08

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