Seeing what your body does automatically every day

This chapter is about your life as an organism. As Chapter 1 explains, organism is the fifth of five levels of organization in living things. Although the word organism has many possible definitions, for the purposes of this chapter, an organism is a living unit that metabolizes and maintains its own existence.

In this chapter, you see why your to-do list, crowded as it is, doesn’t include items such as Take ten breaths every minute or At 11:30 a.m., open sweat glands. The processes that your body must carry out minute by minute to sustain life, not to mention the biochemical reactions that happen millions of times a second, can’t be left to the distractible frontal lobes (the conscious, planning part of your brain). Instead, your organs and organ systems function together smoothly to carry out these processes and reactions automatically, without the activity ever coming to your conscious attention. All day and all night, year in and year out, your body builds, maintains, and sustains every part of you; keeps your temperature and your fluid content within some fairly precisely defined ranges; and transfers substances from outside itself to inside, and then back out again. These are the processes of metabolism and homeostasis.

 

Transferring energy: a body’s place in the world

The laws of thermodynamics are the foundation of how the physics and chemistry of the universe are understood. They’re at the "we hold these truths to be self-evident" level for chemists and physicists of all specialties, including all biologists. The first law of thermodynamics states that energy can be neither created nor destroyed — it can only change form. (Turn to Chapter 16 for a brief look at the first law and other basic laws of chemistry and physics.) Energy changes form continuously — within stars, within engines of all kinds, and, in some very special ways, within organisms.

The most basic function of the organism that is you on this planet is to take part in this continuous flow of energy. As a heterotroph (an organism that doesn’t photosynthesize), you ingest (take in) energy in the form of matter — that is, you eat the bodies of other organisms. You use the energy stored in the chemical bonds of that matter to fuel the processes of your metabolism and homeostasis. That energy is thereby transformed into matter called "you" (the material in your cells), matter that’s "not you" (the material in your exhaled breath and in your urine), and some heat radiated from your body to the environment.

Hetero means "other", and tropho means "nourishment". A heterotroph gets its nourishment from others, as opposed to an autotroph, which makes its own nourishment, as a plant does.