"Life is wondrous! Life is grand! Life is one of the greatest things ever! Just one question...what is life?"
Biology is the study of living things but is there a universally accepted definition of "living things"? Well, not exactly, although pretty much everyone agrees that biology is not the study of rocks.
Nowadays (early 21st Century), biologists tend to think of "life" more as something you describe rather than something you strictly define.
On this page, we will give a quick check-list that you can use to see whether or not you count as an "earth life-form."
All living things on this planet share specific:
Ingredients, as well as specific Behaviors.
The "ingredients" of living things are primarily water and complex organic molecules. An "organic molecule" is a carbon-based molecule.
The organic molecules in living things are more complicated than the molecules that normally occur in non-living things. So, to get these "deluxe" molecules, the cells of living things have to make them themselves.
At a more atomic level, 99% of the human body is made up of these four elements: carbon, hydrogen, nitrogen and oxygen (1).
As you may have heard (the rumor's been out for hundreds of years now), these basic ingredients are organized into units called "cells" that are alive and that are sometimes organized into larger organisms called "multicellular organisms" (things like people, trees and snails) that are also alive.
The "behaviors" of all life on earth start with the behaviors of cells:
(1) storing and exactly following precise instructions
(genetic information stored in DNA) in order to build
the complex organic molecules that run the cell.
These cell-running molecules are primarily proteins and they take charge by being enzymes that catalyze chemical reactions, antibodies that watch out for foreign invaders, etc.
The constant busyness of the proteins is what causes cells and (ultimately) organisms made out of cells to do the things we all recognize as "life-like".
And that brings us to our next set of behaviors - behaviors found in both individual cells and organisms made up of cells:
Cells and those of us built out of cells all:
(2) monitor our surroundings (bacteria can sense food and so can we;
even those "do-nothing" plants grow towards the light).
Monitoring our environment allows us to:
(3) purposefully collect matter and energy from the world and move away from threats (both bacteria and people move towards things
they can eat and away from dangerous situations).
But of course, that's not all because matter and energy are no good to us unless we:
(4) convert the gathered matter and energy into fuels and building materials that we can use, and then:
(5) Use these fuels and/or building materials to monitor, develop and maintain ourselves (cells are constantly checking-over and rebuilding
themselves and our bodies are constantly checking-over and repairing themselves as well).
In these ways, living things take charge of their own destiny in a way that non-living things never do.
But that's not all to the story! Sometimes some living things show even more initiative and create more living things, which leads us to our final category of behaviors - behaviors that involve cells, invidual organisms and species:
Sometimes - given the right lighting - an individual member or individual members of
a species:
(6) reproduces. When this happens, the individual creature or
creatures creates a new creature that has a lot but not always all of the
genetic information of its parent(s).
In this way similar but slightly different creatures come to be, creating
genetic variety which allows:
(7) groups of living things to adapt over time to new and/or changing environments.
In short, we are energy and matter using energy and matter to follow precise instructions that cause us to use energy and matter to gather energy and matter, using this energy and matter to develop and maintain ourselves in such a way that will allow us to keep being able to gather and use energy and matter.
Oh - and then, sometimes we divide in two or get married or whatever is customary and create new beings with genetic information similar to but not always exactly the same as our own.
Round and round it goes! How can such things be?
Questions of that sort are outside the scope of this website. However, we could talk a little about a detail or two. Like, for example,
How exactly does a cell use energy-sources from outside of itself to power all its activities?
FT Exploring already has some pages touching upon this topic (like photosynthesis basics).
However, I've written a couple of pages focusing just on the basics of cellular metabolism.
My reason for making these pages is that I cannot seem to get through a conversation without someone saying something like, "have you heard anything about this ATP stuff? I hear that it is the main way our cells transfer energy from the food we eat into all the cellular activities that keep us alive but that's like pretty much all I can get out of anybody...its like some kind of a molecule or something?... oh, and then there's this other molecule that cells are constantly using as something called a "reducing agent"... have you heard anything about any of this? Seems to be really important, like we'd all die if our cells weren't constantly doing all this transferring-of-energy and building-of-molecules and what-have-you, but when you want to talk to somebody about it, they always get all evasive...what're they hiding? Should I worry about it or what?"
The short answer is that it isn't anything to worry about but if you are interested in some of the details of how cells manipulate energy and matter, have a look at cellular metabolism.
Page Last Updated: 9/5/2011
1 p. 247 of Braving the Elements by Harry B. Gray, John D. Simon and William C. Trogler; copyright 1995 by University Science Books; ISBN 0-935702-34-2
