What are these living units called cells? Much like mini-fiefdoms, cells have all the equipment and expertise necessary to carry out the functions of life. A cell can eat, grow, and move. It can perform necessary maintenance, recycle parts, and dispose of wastes. It can adapt to changes in its environment; and it can even replicate itself.
Despite these similarities, all cells are not equal. Some are truly self-sustaining, as with single-celled bacteria or yeast, whereas others live communally, sometimes as part of complex multicellular organisms. Cells also differ in size. Although cells can be quite large — consider a frog's egg, for example — most are too small to see with the naked eye. Indeed, the development of light microscopy was essential to man's discovery of cells.
Don't be lulled by familiar schematic drawings of oval-shaped cells, either. Real cells are three-dimensional, of course, and they exist in a variety of intricate and remarkable shapes. For instance, a single human nerve cell can be over one meter long, extending from your backbone to your big toe. Compare that with the cells that line your small intestine, which have dozens of tiny, fingerlike projections to maximize the surface area across which nutrients can pass.
But how, exactly, do cells accomplish the complex tasks of life? What tools and materials do they need? And what are the key characteristics that define a cell? This unit answers these questions and provides a basic overview of the inner workings of the cell.
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