2. How do you know if something is "alive?" This may seem like a rather straight forward question, but it is not as easy to answer as one might think. Defining the characteristics that all living things share or have in common is actually rather complicated because there are so many different types of living organisms. When we consider all the different species of animals, plants, fungi, bacteria, etc. that exist on our planet, it is clear that "life" as we know it is wildly diverse.
3. Scientists have come up with a list of criteria that defines life. The only problem is not all scientists agree on the list. Some say there are 5 characteristics that define something as alive, others say 7 or even more. Frankly, it really depends on whom you ask. For the most part however, despite everyone having a different number of characteristics, most scientists generally say the same thing, with some minor differences.
4. And n on-living is not the same as dead . Dead refers to something that was once alive and no longer is. We call anything that is or was once alive organic . Organic material has molecules made up of carbon and hydrogen, like sugars, fats and proteins. Anything that was never alive (rocks, water, metal) we refer to as inorganic .
5. So how are living things different than non-living things? We know that a tree is very different from a bird which is very different from mold, but how are all of these things different from a rock? When asked what all living things have in common, most people will respond with answers like "a living thing can move", or that "it eats", or "breathes." Although many living organisms can do these things, not all of them can--and some things that are definitely not alive can do them--so these are not good indicators of life. To define "life," we need to find qualities that ALL living organisms possess and that non-living things do not.
6. The 5 Characteristics that all Living Things Share Organized Metabolize Reproduce Respond Evolve
7. All Living Things are Organized This means that all living things follow an organized structure. This organization is based on the smallest unit of life: the cell . All living things are made up of at least one cell. Even though cells can have different functions and different structures that help them perform different tasks, every cell is organized (put together) in a similar way.
8. All Living Things Metabolize In order to stay alive, all life forms must be able to take in chemicals from their environment, use these chemicals as a source of energy, then get rid of its waste. This energy can be used for storing and breaking down chemicals, building or eliminating materials inside of the cell--or in other words, for growth. The ability to do this is called metabolism . Not all life forms do this in the same way—but all life can.
9. All Living Things Reproduce All life forms are capable of making more of the same kinds of life form. One of the primary functions of any organism is to perpetuate (or continue) its existence by replacing itself. Living things can reproduce either asexually (which means one parent) or sexually (which means two parents).
10. All Living Things Respond Living things constantly respond to changes in its environment. When changes occur, it reacts . This means it makes changes to itself that better its chances of survival. A trigger that brings about a reaction is called a stimulus . When an organism reacts to a stimulus, this is called a response . Despite changes that occur outside the organism, the "internal environment" remains constant or unchanging, which is called homeostasis .
11. Living Things Evolve Traits are inherited from the parents. Sometimes, variations occur If the variation helps the organism survive, then that successful trait can be passed on to the next generation. More drastic variations can occur, which are called mutations. Some mutations are beneficial and give the organism a better shot at survival—This is how an organism evolves.
