|MadSci Network: General Biology|
Questions from a 20 yr old: Are metals made of cells? Are only organic things made of cells? I was under the impression that rocks have a cellular structure. What kinds of things do not have cells? Is having cells the characteristic that defines something as living? The term “cells” comes from Robert Hooke’s 1665 book, Micrographia. In this book, Hooke describes a cross section of cork as made up of boxlike cells. He also reported seeing a cellular structure in wood and in plants. Hooke made this and many other important contributions. See http://www.ucmp.berkeley.edu/history/hooke.html Metals and inorganic things are not cellular in the sense that organic things, or let’s say living things, are made of cells. But there can be a “cellular” structure to metals and other materials. First, some metals can be “foamed”. This is a new specialty material and it gives good strength for weight. A picture of it looks “cellular”, as would a picture of any foam, which is a matrix of bubbles. For a picture see: http://www.spp-metallschaeume.uni-erlangen.de/ Metals are made of many small crystals called grains. Metals with many small grains are stronger but they are less ductile. These grains can be made to grow until they impinge upon adjacent grains, this makes the metal tougher. The grains are sometimes large enough to be visible under an ordinary light microscope or even to the unaided eye. The spangles that are seen on newly galvanized metals are grains. With iron, adding carbon keeps the crystal grains from sliding over each other. This makes steel, which is harder than iron. A cross section showing these microscopic crystals can make one think of a “cellular” structure. Rocks can also be made of small crystals that can give it an apparent “cellular” structure. Crystals occur in areas where the atoms are arranged in a regular pattern. In general, things like glasses and plastics and rubber, do not have crystalline areas, they are just continuous substances. But the grains and crystalline areas of metals and rocks are nothing like the cells that make up life. The cells of life are mostly water and protein, and they have a cell membrane around them. They also contain DNA, which has the information needed for growing and producing new cells. All living things are made of cells and all cells come from other cells. These are the two basic tenets of the modern cell theory of life. But don’t worry about any question at any age. And remember, even the experts can get things wrong. A few years ago, a new extremely small form of bacteria, called “nanobacteria”, were found using an electron microscope. Alas, it seems these nanobacteria were just very small inorganic crystals. Mike Conrad.
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