THE BEECHMONT CREST GUIDE TO BIOLOGY
What, exactly, is life?
Since early childhood, you have intuitively realized that some things are alive while others aren’t. Scientists have compiled a list of criteria which separate the living from the inanimate.
Sensitivity: Living things respond to stimuli. If you pull a dog’s tail it may bite you. The tomato plants in your garden grow toward the light. If you walk into a dark room, your pupils will dilate to allow more light to enter your eyes.
Order: Life is comprised of a series of hierarchical structures. For example, atoms form a molecule. Molecules make up the functional elements of the cell---known as organelles. Cells are the building blocks of complex organisms.
Growth: Living things grow and develop. Inanimate objects don’t.
Reproduction: Living things will get you more living things. Some living things reproduce with the help of others of the same species (sexual reproduction), while others can do it all by themselves (asexual) reproduction.
Internal controls: All living things regulate internal processes; and all living organisms contain an internal set of transport systems. Wastes, hormones, and nutrients are a few of the substances that living things move around internally---usually without conscious effort. Living things can also control their own body temperature. (This is known homeostasis).