one life or a community?

Y

yayacatfight

Registered Senior Member
what is the generally accepted definition of a living entity? is a cell alive? i have heard you can nurture a single cell for 14 days in a test tube. if this is true is a human being not more like a community than a single living thing?

thanks
 
One might say, that all the cells in a human body are dependent on each other, and are therefore one living entity. But of course, you make a valid point that a multicellular organism is a community of cells. But most cells are specialized and couldn't live without other specialized cells.

Cells in culture can be sustained because we provide for them a suitable environment. It is however a highly artificial environment.
I have grown a prenatal mouse tooth for 2 months in culture myself. It is not so effecient as a tooth growing in the body though. And at the end they perish.
 
interesting. so you're saying that dependence is the key element. but using your implied definition i think it could be argued that humans are dependent on trees for oxygen and therefore a human is not a living entity.
 
exactly, without the queen, a termite nest, or a beehive withers. they are dependent on the queen for survival. but does that meen the worker ant is not a living entity on its own?
 
Many say ant/ termite colonies are a living organism for a number of reasons. Each ant being a piece the organism is willing to lose in order to survive.
It is on this train of thought that the gaia theory(the earth as a super organism) arose.
If you are to say a human is a living entity there is no reason to say the earth is not.
 
There is the idea that the origin of mutli-cellular organisms was multiple single-celled organisms living in a symbiotic state.

Which makes a lot of sense.

If that is true, then maybe that's all we still are?
 
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Im not quite so sure about Gaia. As a species we would rather destroy the rest of the planet than go extinct ourselves. The balance of nature is more of a myth than anything else.
 
Originally posted by Clockwood
Im not quite so sure about Gaia. As a species we would rather destroy the rest of the planet than go extinct ourselves. The balance of nature is more of a myth than anything else.
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Yes but as a species we harm ourselves all the time. Things like smoking and drugs aren't exactly beneficial to us; so saying that Gaia doesn't make sense because that would mean the Earth is hurting itself...doesn't really hold true. Humans as a living thing harm themselves so there's still nothing to say that the Earth as a whole isn't alive. Although I do see your point in it being a bit absurd; but it is good to think about new avenues of life.

As for the whole 'single cell being alive' thing. Maybe we could think about it in terms of reproduction. It may be true that you can keep a single cell alive in culture, but can that single cell grow and divide to produce viable offspring? So although multicellular organisms are a community of cells dependent on each other, they still have to work together as a whole to reproduce and the offspring have to contain the same kinds of cells to survive. So this group of cells can really only survive with each other and so as a whole they are said to be a single living thing.
 
Originally posted by one_raven
There is the idea that the origin of mutli-cellular organisms was multiple single-celled organisms living in a symbiotic state.

Which makes a lot of sense.

If that is true, then maybe that's all we still are?
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Not anymore. That still applies to some protozoans (Volvox), but we've come a long way from there. Just think of our mitochondria. No one would think they're symbiotic organisms living within us anymore, but the truth is they probably started as such.
 
Originally posted by Konek
Not anymore. That still applies to some protozoans (Volvox), but we've come a long way from there. Just think of our mitochondria. No one would think they're symbiotic organisms living within us anymore, but the truth is they probably started as such.
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So, where is the line drawn?
If the organism can survive on its own?
But aren't there some parasites that can not live without the host?
What is the difference between a multi-cellular organism and a collection of organisms living in a co-dependent symbiotic state?
 
Originally posted by one_raven
What is the difference between a multi-cellular organism and a collection of organisms living in a co-dependent symbiotic state?
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Originally posted by spuriousmonkey
Genomic content?
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Hmmm. That is true, but still not enough. I guess the clue would lie on the development from a single zygote. This would allow to include the mitochondrial DNA (present in the zygote) as our own.
 
A zygote splits in two in order to produce twins. So you still have two entities, even if the separation is incomplete.
 
Are there such cases? I'd draw the line at the brain, but that's just me.
 
Quoted from http://www.geog.ouc.bc.ca/physgeog/contents/9a.html

The four main types of biological entities described above share some unique characteristics that can allow us to distinguish them from non-living things. These characteristics are:

(1). Organisms tend to be complex and highly organized. Chemicals found within their bodies are synthesized through metabolic processes into structures that have defined purposes. Cells and their various organelles are examples of such structures. Cells are also the basic functioning unit of life. Cells are often organized into organs to create higher levels of complexity and function.
(2). Living things have the ability to take energy from their environment and change it from one form to another. This energy is usually used to facilitate their growth and reproduction. We call the process that allows for this facilitation metabolism.

(3). Organisms tend to be homeostatic. In other words, they regulate their bodies and other internal structures to certain normal parameters.

(4). Living creatures respond to stimuli. Cues in their environment cause them to react through behavior, metabolism, and physiological change.

(5). Living things reproduce themselves by making copies of themselves. Reproduction can either be sexual or asexual. Sexual reproduction involves the fusing of haploid genetic material from two individuals. This process creates populations with much greater genetic diversity.

(6). Organisms tend to grow and develop. Growth involves the conversion of consumed materials into biomass, new individuals, and waste.

(7). Life adapts and evolves in step with external changes in the environment through mutation and natural selection. This process acts over relatively long periods of time.
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