I AM SOMETHING LIKE a big city. I have dozens of power stations, a transportation system, a sophisticated communications setup. I import raw materials, manufacture goods, and operate a garbage-disposal system. I have an efficient government-a rigid dictatorship, really-and I police my precincts to keep out undesirables. All this in something my size? It takes a good microscope to even see me, and a super microscope to peep inside my metropolis! I am a cell, one of the 60 trillion in your body. The cell is often called the basic element of life. Actually, we're life itself. As a rod cell in your right eye, I will speak for the vast population of which I am a member.
There is no such thing as a "typical" cell. We are as different in form and function as a giraffe and a mouse. We come in all sizes, the largest of all being an ostrich egg. From there we scale down to a point where a million of us could sit comfortably on the head of a pin. And we come in a variety of shapes-discs, rods, and spheres. We participate in everything you do. You lift a suitcase and think your arm is doing the job. Actually, it's invisible muscle cells, contracting. You ponder which necktie to wear: it's brain cells that do the pondering. Or you shave your face: nerve and muscle cells perform the entire operation. For that matter, the facial hairs you chop off were produced by other cells.
My task as a rod cell in the eye is to catch faint light-say the twinkle of a star - simplify and change it into an electrical signal, which I then send to your brain. If enough signals arrive, you "see" the star. Since each of us 250 million rod cells in your eyes contains 30 million molecules of light-catching pigment, we naturally use a bit of electricity. To generate it, I have some thousand mitochondria-super minute, sausage-shaped power stations, that burn fuel (sugar), produce electricity and leave "ash" (water and carbon dioxide) behind. In this complex chemical process they synthesize a substance called adenosine triphosphate- ATP for short. It is the universal power source for every living thing, from rhubarb to clams to man. When, there is need for energy - to make the heart beat, to expand the chest in breathing, to blink an eyelid - ATP breaks down into simpler substances, "releasing" power as it does. As long as you live, there will be this call for energy and ATP. Even in deepest sleep there is a torrent of activity-cellular furnaces burning to keep the body warm, brain cells discharging electricity to make dreams, heart cells pulsing to keep the blood flowing. The breakdown (and building up) of ATP is constant. All of us cells have mitochondria, with one notable exception, red blood cells. Since they do no manufacturing and are swept along by the bloodstream, they have no need for power.
Perhaps the ultimate wonder among cells is the female egg, as in the body of your mother. Once fertilized, this single cell divides over and over, until there are the two trillion cells of a baby. Phenomenal as such multiplication is in itself; the truly striking thing is the enormous amount of information stored within the fertilized egg. That tiny fragment of life contains the blueprint for building that complex chemical plant, the liver. It stores coded information on hair color, skin texture, body size. It knows when to shut off growth of a little finger. Even at the outset, it knows approximately how bright Joe may be years later, what diseases he might be susceptible to, even his general appearance.