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So I'm pretty sure your are all aware of what a cell is the microscopic organic units that make up all life.

Well they don't have to be microscopic. An unfertilized chicken egg is a single cell. will smith showing off his eggsalent egg Here in this link is record of one of the largest single cells on earth. It's a whale shark egg; it's a foot long, 5.5 inches wide, and 3.5 inches thick. Almost the size of my head. I think this one is the largest single cell organism in the world (Caulerpa taxifolia). So I know cells can be supersized.

So I really want to know could there realistically be a unicellular life form about the size of a human that could eat/absorb other organisms and survive in the wild? Or is it impossible because it would be really weak, pop like an chicken egg and die instantly?

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  • $\begingroup$ I really appreciate you put in Will Smith beside the egg for size comparison but is that what I think it is... shark ovum? $\endgroup$
    – user6760
    Commented Nov 7, 2016 at 12:43
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    $\begingroup$ LOL nononono... I'm sorry the picture is will smith and a chicken egg I found on the internet and photoshoped together. The largest egg in the world however is a whale shark egg which looks nothing like that. $\endgroup$
    – X_Wera
    Commented Nov 7, 2016 at 12:51
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    $\begingroup$ The title made me think of "germs being eaten by a giant man" instead of "giant germs that can eat men". $\endgroup$
    – Achilles
    Commented Nov 7, 2016 at 13:32
  • $\begingroup$ You may want to ask just one of the questions to avoid the question being seen as to broad. $\endgroup$
    – Bellerophon
    Commented Nov 7, 2016 at 22:11
  • $\begingroup$ @ Bellerophon Yes probably I will remove the follow up questions. $\endgroup$
    – X_Wera
    Commented Nov 7, 2016 at 22:14

3 Answers 3

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No.

There's a commonality between the examples you gave, namely they are both eggs. For most animal life, the largest cell is the egg-cell, this is true for humans as well. The human ovum is around 0.12mm in diameter.

The largest uni-cellular life gets to around 4-9 cm, slightly larger than a chicken egg. The largest single celled organism (Caulerpa taxifolia) actually looks a lot different than most macroscopic uni-cellular life.

Link (wikipedia)

It can only get so big because it has a unique structure that increases surface area, this life form also has multiple nuclei, so it's a bit of cheat. They don't get larger than 30cm high.

When a uni-cellular circular organism gets larger*, its membrane surface area increases by $4\pi(\Delta r)^2$ whereas its volume increases by $\frac{4}{3}\pi(\Delta r)^3$, where $\Delta r$ is the increase in radius. In other words, the interior grows faster than the membrane.

Cells need a large enough surface area in order for food and waste to move in and out. Large cells also require thicker membranes, making this transport of food and waste more difficult. The result is that most uni-cellular life remains microscopic, and none can get as large as you want.

*Of course uni-cellular life isn't exactly circular, but this is for easier calculation.

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  • $\begingroup$ But then this comes down to what we know. Since there's no hard-science tag, it could be postulated that non-carbon based lifeforms could potentially take a large, unicellular form. $\endgroup$
    – Jesse Williams
    Commented Nov 7, 2016 at 15:05
  • $\begingroup$ @JesseWilliams The question has the "Reality Check" tag though. Obviously we can never say something is improbable, but there's no reason to suggest that it is possible, and from what we know, it isn't. $\endgroup$
    – Feyre
    Commented Nov 7, 2016 at 15:14
  • $\begingroup$ Sure, but with the creature-design tag, it is plausible that it could happen, despite not existing with terrestrial biology (so far as we know). $\endgroup$
    – Jesse Williams
    Commented Nov 7, 2016 at 15:15
  • $\begingroup$ According to Science Daily Caulerpa taxifolia can grow to a length of six to twelve inches. $\endgroup$
    – Thom Blair III
    Commented Nov 7, 2016 at 18:25
  • $\begingroup$ @ThomBlairIII I mentioned that one, and that it grows up to 30cm, which is the same as 12in. $\endgroup$
    – Feyre
    Commented Nov 7, 2016 at 18:35
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There are significant problems but I'm not sure they're insurmountable. The resulting cell would be very unlike anything we know of though.

As far as I see it, the problems are basically problems of transportation. 1. A cell relies on diffusion to get a lot of the stuff to where it needs to be, but things just moving around randomly via Brownian motion won't cut it if you're that large. In a normal cell there are also protein fibers and motor proteins that tug along whatever-filled vesicles along those fibers to where the stuff needs to be. Those would also very probably be ineffective at larger scales. 2. A single nucleus would not get all the instructions for the production of additional proteins etc. to the places they have to be in a timely manner. Maybe there could be a main nucleus telling sub-nuclei (telling sub-sub-nuclei etc.) what to do? 3. The thing would be really slow at processing external stimuli without nerves.

You basically need a circulatory system (and a equivalent of lungs). Maybe it could constantly "gulp in" vesicles of air (or oxygen rich water). If you don't want a circulatory system maybe a "pump" could at least swirl the plasma around so the nutrients and oxygen get distributed. And there would have to be a mechanism that collects waste products into ever greater vesicles that can then be deposited.

If the plasma congeals the moment the membrane is pierced, the thing might avoid "popping".

I don't think it would make for a very intimidating or even efficient organism, but I could imagine such a thing eking out an existence on the sea floor if there's not much competition. Eating giant isopods that are too full of dead whale to move.

(also I'm new to this site - if it is considered impolite to post an answer to a question that is already clicked to be displayed as answered, I apologize and won't do this again)

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  • $\begingroup$ It's not impolite at all. Even though a question has been answered, new light can be brought to it. $\endgroup$
    – Masclins
    Commented Nov 9, 2016 at 10:20
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your big problem is that since it is not made of specialized cells, it is basically a giant moving wad of easy food for anything with teeth.

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