Not too long ago, we studied the characteristics of life in my biology class. It was all quite interesting and worthy of sharing with the entire world.
First of all, we have to figure out what characteristics make something living or not. We cannot just say everything on the planet is alive. No, we have to have some kind of distinction between living and non-living. So, scientists tried to figure this out; they went through a lot of questions and eventually came up with the following.
Characteristics of life (in no particular order):
- Stimulus response
- Energy – harvesting and using it
- Organization/made up of cells
Just remember them as the Lively 7. Or
Everything that is alive has to respond to changes. This is called a “stimulus response”; life needs this. One kind of response would take form in plants’ leaves turning to capture more sunlight for photosynthesis.
Stimulus response is usually made by movement or chemical changes and can keep a steady balance in a healthy environment.
But, this response isn’t just a meaningless juncture of movement or changes, no; this response requires something unique but still can not define life by itself.
If you had water, which is not alive, and you tried to make it respond to stimulus . . . it would do it. For example, let’s say our water is peacefully running down a river. Then, suddenly, a boulder falls from a nearby slope and jams up the river. Now, is the water going to stop flowing? Is it going to say, “oh well, I can’t respond to stimulus so I cannot move forward?” No!
This water will eventually make its way around or above the rock. This required a response to stimulus. Now, the water isn’t alive, but things that are alive require stimulus. Response to stimulus is just one aspect of life, you need all seven, remember?
Homeostasis is a process which by certain organism has a steady balance of certain attributes that maintain an equilibrium. Of course, the response to stimulus is a way of getting to homeostasis (balance). But, homeostasis is all about keeping that balance that stimulus response has given. Basically, stimulus response gets an object at a balance and homeostasis has to keep it there. This is very important.
This balance can be shown with an example using frogs and flies. When a new group of flies are born, the frogs are greatly outnumbered. However, their response to a change, (a stimulus), kicks in. They start filling their stomachs and finally they make a balance between the fly population and the frog population. The number of flies is not the same as the number of frogs but, there is a balance. Now, all the frogs have to do is keep that balance.
However, with more food, the frog population will grow and be able to support more frogs. Then, the frog population will outnumber the flies and unless the frogs can be maintained by birds or other creatures, the flies will be taken care of, forever!
This is homeostasis. There has to be a balance. The fly population may grow, then it might decrease as frogs increase. But then it could increase again as frogs decrease. Then the process could be started all over again. Only when a third or fourth factor is introduced as a predator can the frog/flies population stay in balance.
Homeostasis is a requirement for life but non-living things can mimic it.
Let’s use our water analogy again. The rock falls on the river, dams it up and the water has to respond. It overflows the rock or goes around. Currently the rock is prevailing. The water, however, with the right amount of erosion will eventually degrade that rock until it is even. It may be slow but it is responding to stimulus and trying to maintain homeostasis.
Adaptation is probably one of the strongest characteristics both for living and non-living objects. You see, adaptation to one’s environment is something that can be controlled ruthlessly by natural forces, both for living and non-living organisms.
First of all, for living things, adaptation is an important process whereby the living things change in order for them to survive in a changing environment. One way adaptation can be shown is through forms of beaks in birds.
So imagine this: a new group of many species of birds fly into town. In this town, you have a whole lot of insects and worms for the birds. Eventually, you have the birds who like the grasshoppers eating those. The ones who like the worms are getting those. The ones who love the other flying insects get those. However, there are many more worms than other insects.
However, as time goes on we start to see something change. Since there were more worms in this area than any other insect, the birds that eat the worms are growing exceptionally larger numbers. As well, their beaks are changing. Because they have to dig in the ground to get their food, the few birds that had thinner beaks were ones that got to eat more. As the years went on, the longer, skinnier beaked-birds’ population boomed until they had suppressed many of the other birds.
You see, these birds didn’t require any new information to adapt. Instead, the ones with the closest to best tools for worm-catching were the ones who survived the best in the new environment. As time went on the longer, thinner beaks were the main worm-eating tool for these birds, thus, they flourished.
Really, there was no new information, only this: the birds that had the best equipment developed and used that equipment and eventually prevailed above their peers.
However, it is the nonliving things that can be changed the most according to their environments. Many examples of this can be seen with ice, rock, wind, etc. Rock can be eroded by chemicals or weathering and these change according to their environment while using response to stimulus and maintaining homeostasis. Sand can be made from erosion on rock and then shaped into sand dunes by wind.
Probably the most important aspect of life, to us at least, is its ability to reproduce. Without reproduction, all life would have been done with soon after it had been created.
Interestingly enough, living things are not the only things that reproduce. But, before we discuss that, we must first discuss how living things reproduce.
The truth is, the reason living things can even reproduce is because of the cell. This tiny tool of living things makes a copy of its DNA and then splits itself in two. This is the first reproduction done in the making of a living, multi-cellular thing. Then, as those cells split and reproduce, the living thing is made. That happens with all living things . . . they reproduce by cells.
Anyway, when non-living things reproduce it does not reproduce by cells but by other forces. You see, nonliving things can reproduce, but not by the way living things do. For instance, a plant can reproduce through cells but a cloud cannot. It can reproduce but not in the same instance as living things.
For clarification some non-living things reproduce, in our case, fire, by using fuel to spread themselves out. If the fire runs out of fuel it dies off, but, then again, it was never living.
So, technically, non-living things cannot reproduce, but they can reproduce in a different manner.
Now, something that non-living things cannot ever do is obtain and use energy. They just can’t do it. For instance, have you ever seen a bucket of water chasing down a gazelle? Or maybe you have seen a flash of lightning go streaking across the sky at lightning speed (no pun intended) to pick off a goose for lunch? Or, perhaps, you have witnessed a computer pounce on a human, suddenly, and overtake and dine on them?
Of course, you have never seen something like that because non-living things cannot do that. Those things that are not living can not seek, obtain and use energy like you, an animal, plant, or any other living thing can. Ultimately, in our SHAREGO, gathering and using energy is the first criterion that cannot actually (even though others one got really close) be done by non-living things.
Since it is one of the Lively 7, seeking, obtaining and using energy is a vital characteristic of life and its survival. If you think about it, energy literally consumes our life.
Everyday, unless you are stranded in the desert or something, you eat food to obtain energy. Your body uses this energy. Everyday, trillions of animals eat plants, insects, other animals, etc. They do this to obtain and use energy. They are living things so they need energy. Then, everyday, quadrillions of quadrillions of plants obtain and use energy from the sun through photosynthesis.
Bottom line: all living things seek, obtain and use energy.
All living things start from one cell. As these cells multiply they form the living thing, in our case, a cub tiger. And, as the cells form the living thing, that thing eventually becomes a distinguishable, visible object. Basically, it finally becomes a baby tiger cub and is born.
Then, as the baby cubs grows to seek, obtain and use energy, it begins to grow. Based off the amount of energy it can obtain, the cub will grow and be very productive. The tiger cub grows because its cells reproduce. Without the steady production and reproduction of muscle cells, bone cells, etc. the cub wouldn’t grow.
With non-living things, this is not the case. Although non-living things can appear to be growing (like a river flood, clouds getting bigger, etc.) they do not grow in the same sense as living things. Just like the reproduction thing. Non-living things can reproduce but not nearly in the same way as living things; this separates them.
Thus, non-living things cannot grow in the same sense as living things and thus it can be reserved for living things alone.
Organization is a very important part of life. Non-living organisms can have organization but they can’t have cellular organization as they cannot be made up of cells.
The cell is the smallest object in the universe that can still perform all the processes of life.
The absence of cells in an object clearly states that this thing is not living. A cell, after a certain amount of time, will reproduce by copying itself and breaking into two. These daughter cells will then break apart and form two more daughter cells. So on and so forth.
Think of a piece of pizza. The longer you leave that piece it is going to break down; it isn’t going to start getting bigger because it has cells reproducing. Only a living thing can do that. Imagine a reptile. It is born, as it grows more and more cells reproduce in its skin, muscles, bones, etc. The baby grows. And grows. Grows. And it doesn’t stop reproducing cells until it dies. It is one of the easiest ways of determining if something is alive.
Well, there you have it: the seven characteristics of life. Without these little things in on object you do not have life. Amazing isn’t it? So, next time you hear your little brother or sister ask you, “on Sesame Street, is Zoey’s Rocko alive?” You can sit down with him or her and break the news that Rocko is not alive. Just don’t tell Zoey that.