The Breadth of Function in One-Celled Animals

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DonSchaeffer
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The Breadth of Function in One-Celled Animals

#1 Post by DonSchaeffer » Sun May 10, 2020 7:37 pm

How can a single cell handle all those specialized functions: motion, sensation, food acquisition, digestion, reproduction, etc.? Why do we need so many cells to accomplish these things? How many functions do our individual body cells potentially handle? Sorry, the question occurred to me and now I'm looking for an answer. How complete are microbes?

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Re: The Breadth of Function in One-Celled Animals

#2 Post by Hobbyst46 » Sun May 10, 2020 10:09 pm

Decades ago, answers to these questions were found in middle high school biology textbooks. Nowadays you can also find them by googling, for example, "overview cell". Here is just one small example of a plethora of stuff:
https://www.youtube.com/watch?v=cbiyKH9 ... e=youtu.be
A unicellular creature is able to survive in a pond, for a while; and common protists behave as you mentioned - move, eat, reproduce etc (some of them apparently think and remember as well)... some of the jobs are done via organelles, like a primitive light sensor "eye" or food opening "mouth".
A multicellular organism, specific groups of cells undergo transformation into highly specialized cells that form limbs, function in harmony, so the creature can survive longer and under more diverse conditions: out of water, in variable climates, can nurture offspring, communicate with other creatures, create shelters and achieve larger body dimensions, from millimeters to meters to a few dozen meters.
Here are just a few of the large number of specific tasks our body cells perform:
Absorb oxygen from air;
Bind oxygen within the blood stream (red blood cells);
Fight and destroy toxins, viruses, bacteria (white blood cells);
Sense electrical pulses and transmit them (nerve cells);
Protect the inner parts of the body from mechanical and other external damage (skin cells)
Exert force to enable physical efforts (muscle cells);
Perform thinking (the little gray cells);
Sense light and transport the signal to the brain (vision cells);
A "microbe" is a bacterium, all complete unicellular organism sans nucleus; a large portion of the human body is thought to consist of bacteria...
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DonSchaeffer
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Re: The Breadth of Function in One-Celled Animals

#3 Post by DonSchaeffer » Sun May 10, 2020 11:35 pm

Thanks for your response. It just makes me more curious. I know they are tiny and can only live in water for a time. But they can do so much with one cell. Parts of the cell act as light sensors, some act to move cilia for swimming and moving, parts act as a kind of governance in the interest of the animal. One cell can articulate so many functions--how--and still be just one cell. Some of the images in this forum show these creatures which such detail that they look like real furry animals. Their species have been around longer than ours and some of them are apparently immortal.

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Re: The Breadth of Function in One-Celled Animals

#4 Post by wporter » Mon May 11, 2020 1:19 am

It is only a big mystery because we haven't figured it all out, yet. But basically it is as was said: a unicellular organism (UO) makes use of internal funtional parts to do the same functions as our organs and supportive structures. Both are complex systems, making use of positive and negative feedback loops to control responses, and lots of canned responses inherent in the structures build by the genetic code. The DNA of a simple one-celled animal can code for the synthesis of tens of thousands of different proteins. That's a lot of potential building blocks for structures, signalling pathways, control loops, etc!

One type of difference is the complexity of the inter- and intra-actions. We use nerve and circulating signal molecules (hormones, etc) for internal communications between parts and with the outside world; the UO doesn't have a nervous system like our, and uses just the signal molecules generated by an organelle (e.g.), or protein structure (from some influence internal or external to the cell wall or membrane), and which signal some other part of the cell to do something.

We don't 'need' so many cells to do all the stuff microbes can do, it is just that we can, so we do. Many UOs can congregate in groups; when they do, sometimes we see specialization by certain cells in certain areas of the group structure, presumably for the benefit of the whole cluster. So it's not hard to see how multicellular organisms evolved. Just another layer or two of complexity, which adds up to enhanced evolutionary possibilities.

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Re: The Breadth of Function in One-Celled Animals

#5 Post by Hobbyst46 » Mon May 11, 2020 5:53 am

Just recalled the books by Richard Dawkins, such as "The Blind Watchmaker", "The Selfish Gene". These are aimed at the general audience, not scientists, and describe and explain evolution and development of organisms and organs. Enjoyable reading.
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Re: The Breadth of Function in One-Celled Animals

#6 Post by DonSchaeffer » Mon May 11, 2020 9:33 pm

Let me ask: Could one of our cells, any cells perform as many functions as the protozoan potentially?

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Re: The Breadth of Function in One-Celled Animals

#7 Post by Hobbyst46 » Mon May 11, 2020 10:02 pm

DonSchaeffer wrote:
Mon May 11, 2020 9:33 pm
Let me ask: Could one of our cells, any cells perform as many functions as the protozoan potentially?
Perhaps not, I think not, but the scope, sophistication and performance level of each of the activities that an individual multicellular creature (primitive worms, crustaceans, let alone mammals) performs are beyond the capability of protists; on the other hand, a huge mass of certain protists can bring us human beings hell...by the mere secretion of toxins, etc...
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Re: The Breadth of Function in One-Celled Animals

#8 Post by wporter » Tue May 12, 2020 12:42 am

Could one of our cells, any cells perform as many functions as the protozoan potentially?
That is like asking "is a Swiss Army knife capable of more than a hammer?" Sure, but if the hammer always comes with a tool box full of other specialized tools, the toolbox can equal the Swiss Army knife, and probably outdo it in terms of overall functionality.

So the short answer is sorta yes. Our cells are each specialized; but they start out as stem cells, unspecialized, each holding all the instructions for all the different types of cells in your body, and are forced down a path of a given narrow specialization by external influences, causing a particular gene expression (i.e., activation and suppression of parts of the genome) turning it into an (e.g.) organ cell. Along with the nuclear DNA, though, there is mitochondrial DNA, that codes for it (and is the probably the result of an evolutionary absorption of a symbiotic bacteria) which complicates matters.

The point being that the set of instructions, i.e., the DNA, for a complex multicellular organism is way different than for a unicellular organism; but they both lead to cells that are capable of many complex functions. But the instruction sets diverged millions of centuries ago, so it's not really legitimate to compare the two any more. In this case, comparisons are indeed odious.

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Re: The Breadth of Function in One-Celled Animals

#9 Post by PeteM » Tue May 12, 2020 3:36 am

Here's one interesting take on the origins of life, from one of our local scientists, David Deamer: https://www.scientificamerican.com/arti ... -suggests/

Dave's notion is that a cell wall is critical to the origins of life - over generations its enclosure makes zillions of evolutionary experiments possible. We Dave's help, we concocted a "Micronaut" visualization of a cell wall forming before our very eyes under a microscope. Basically requires a fatty molecule (we use soy lecithin) with one end water-loving and the other hydro-phobic. It basically turns into a membrane.

Deamer has also been an advisor on space probes -- gave a nice talk to one of my discussion groups on where he thinks we should look for life elsewhere in the universe (basically where something like cell walls can form). He's also got a novel method of DNA sequencing under development (very cheap and fast, but not yet particularly accurate).

It's a pretty cool idea. Build tiny labs (cell walls). Make them semi-permeable. See what wanders in to experiment with the other stuff inside, with successful experiments repeated. Do that for a couple billion years or so. Be amazed today.

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Re: The Breadth of Function in One-Celled Animals

#10 Post by wporter » Tue May 12, 2020 6:03 pm

Unfortunately, the article is behind a paywall, for $6, and your local library, like mine, may be closed for a while, but here's a link to a digital collector's edition with that article, plus more great ones, for not much more $:

https://www.scientificamerican.com/maga ... -issue-3s/

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Re: The Breadth of Function in One-Celled Animals

#11 Post by DonSchaeffer » Tue May 12, 2020 8:23 pm

I've heard commentators say that a microbe "sucks" the content of prey into its mouth or tubule or whatever. How do microbes "suck?" They would have to create a vacuum.

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