Physical Properties of Protoplasm

There are great differences among living organisms, yet all organisms are made of cells. When the most minute organelles of cells are examined, even of very diverse life forms, the differences disappear. Mitochondria, Golgi bodies, ribosomes, endoplasmic reticulum, centrioles all seem to to be the same wherever they are found. This is also largely true of chemical composition. All cells have proteins, fats, carbohydrates, nucleic acids, minerals, and enzymes. This living substance is called protoplasm, and although it may vary within a certain range from organism to organism, the likenesses are certainly more striking than are the differences. All kinds of protoplasm possess the capacity to respond (irritability), the capacity to move within a cell (motility), the capacity to grow, and the capacity to reproduce. What is life? We may attempt to define life by stating of what life is made, or by explaining what life does. Life, however, is more than the sum of the substances of which it is made.