When sitting and watching a fire, it is easy toget the idea that it is alive. It movesdynamically, dancing and sending sparks. It isable to spread across a surface, and move aboutfrom combustible object to combustible object. Itconsumes such materials as wood, converting theminto ash and other byproducts. It needs oxygen,as though it were breathing. However, fire ismost definitely not alive.In fact, none ofthese criteria prove that something isalive!Oftentimes we think that all liferequires oxygen. However, there are many bacteria(called anaerobic bacteria) which do not needoxygen at all! They live down in the soil, underoceans and lakes, and in other areas. To many ofthem, oxygen is a poison! Yet they are definitelyalive. So clearly whether or not something needsoxygen does not show if it isalive.Consciousness as we think of it isprobably not a good determinant for life either. It is highly unlikely that bacteria, fungi,plants, and other organisms think, since they lacka brain or nerves. Yet they are definitely alive. Therefore whether or not something thinksdoes not show that if is alive. This is the samefor movement, because not all living things move-- in fact, many living things move a lot less thanfire! And many non-living things move, such asthe wind or a car.In order for somethingto be considered alive it must have severalcharacteristics and abilities, such as metabolism,growth, reproduction, and response to stimuli oradaptation to the environment. How does firestack up to these requirements?Firecertainly seems able to grow. A small campfirecan quickly grow to the level of a forest fire, soyes, it seems to meet this criterion.Canfire reproduce? Again, it seems able to! Asingle spark can blow to a different location andstart a new fire. That might be consideredreproduction!
Fire is not alive, although it certainly seems tohave a mind of its own! The process of oxidationis when substances react with the oxygen in theair to make oxides (like rust on iron, is ironoxide, and when your mom"s silver tarnishes, thatis silver oxide). When things oxidize, theyrelease heat. Fire is just very rapid oxidation.Heat rises, and makes currents of air thatcirculate as the hot air rises - that is whyflames appear to dance and move around. Fire needsoxygen to burn, and it needs fuel; for somethingto "burst into flames" it needs to be at a highenough temperature. Without any one of theseingredients the fire won"t burn. A flame onearth is in a gravitational field - that is why itis thicker at the bottom. But a flame in the spaceshuttle, in what they call "microgravity"(*)environment is actually round! Pretty amazing -imagine a "flame ball"! (* Actually there isplenty of gravity up there - that is why theshuttle stays in orbit - but it is in a state of"free fall" around the earth so you _feel_weightless.)
Biologists have fought a bit over the basicdefinition of life, but all biologists would agreethat fire is not alive. Remember, not all livingthings feed on oxygen (plants feed on carbondioxide), so that"s not a good definition forlife. Not all living things move (again, plants donot really move), so that"s not a very gooddefinition of life. Not all living things "think",either (plants do not think).What your questionreally comes down to is how to define life. I"vetried to come up with some basic definitions oflife. -- For me, life can be defined by it"smost basic building block -- a cell. If somethingdoes not contain at least one cell, it is notalive. Fire does not contain cells. -- Livingthings contain DNA and/or RNA, proteins whichcontain the basic information cells use toreproduce themselves. Fire does not contain DNA orRNA. -- Living things are made of matter,and you can weigh them. It may be hard to measurethe weight of one bacteria, but you get the point.You cannot weigh fire, because it is simplyenergy. It has no mass. Fire is energy given offwhen matter burns. You can see it, but what yousee is merely light, so you cannot hold it. --Living things grow, and in growing they make newmatter, but it"s not just any old matter. Lifeis organization. All living things make the samebasic things: proteins, fats and carbohydrates,for example. Fire cannot make proteins from theoxygen and hydrogen and carbon it "feeds on", justdestroy proteins. This is a major difference.-- Living things require nutrients andwater, and have complex ways of finding and usingthe things in their external environment that theyneed. Living things also have ways of sensing andresponding to threat or attack.
That"s a great question because fire does havesome things in common with living things. It needsfuel and oxygen. It can grow. It "reproduces" tomake more fires. But fire is also differentfrom living things. For one thing, it is not madeof cells. All living things are made of cells.Also, when fire "reproduces," no informationis passed on. In living things, DNA carriesinformation from one generation to another. Allliving things are adapted to where and how theylive by evolution, which changes DNA over time.Fire is basically the same every time. It may bebigger or smaller, hotter or less hot, or movingdifferently, but that"s all because of theconditions right now, not because of informationit inherited in DNA.Another difference is thatall living things come from other living things.One-celled living things divide to make two newone-celled things. Eggs, spores, seeds, babies,and growing new individuals from parts of their"parents" are all ways to reproduce new life fromlive things. Fire can come from a match, rubbingsticks together, a spark, or other things that arenot fire.So fire is a great example ofsomething that has some characteristics of life.Thinking about ideas like this helps us to reallyfigure out what we mean by life.If you couldmake robots that made other robots, would they bealive?
According to Hickman, Roberts, and Larson (1997),any living organism will meet the following sevenbasic properties of life:1) Chemicaluniqueness. Living systems demonstrate a uniqueand complex molecular organization. 2)Complexity and hierarchical organization. Livingsystems demonstrate a unique and complexhierarchical organization. 3) Reproduction.Living systems can reproduce themselves. 4)Possession of a genetic program. A genetic programprovides fidelity of inheritance. 5)Metabolism. Living organisms maintain themselvesby obtaining nutrients from their environments.6) Development. All organisms pass through acharacteristic life cycle. 7) Environmentalreaction. All animals interact with theirenvironment.Fire is not alive. It does notcontain genetically inheritable information, andarguably does not have a complex organization.
While it is true that fire feeds on oxygen andmoves it is lacking a very important feature to beconsidered alive.
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In order to be considered aliveyou have to be able to reproduce either sexuallyor asexually at some point in your life. Allliving things also contain a genome (DNA), that istransferred to it"s progeny (offspring)