io8 Livmg 



very important part in the life of the 

 cell and of the organism. 



Frequently one or more small round 

 bodies are found within the nucleus. 

 They are called micleoU (new-klee'o- 

 lie; singular, nucle'o-lus). The nucleolus, 

 too, is readily stained. We do not know 

 what work it does in the cell. 



The structure of protoplasm. You read 

 above that cytoplasm appears through 

 the microscope to be a thickish liquid, 

 colorless or light grey in color, contain- 

 ing small particles or granules, and that 

 the nucleus looks much like it, only 

 denser. Exercise 9 will be helpful now. 

 Staining protoplasm with dyes has helped 

 somewhat to bring out its structure but 

 no one can be certain that the stain has 

 not caused changes or produced sub- 

 stances not present in the unstained pro- 

 toplasm. 



Although it seems to be comparatively 

 simple when seen through the micro- 

 scope experiments have shown that pro- 

 toplasm is really a very complicated 

 mixture of many substances. Some of 

 these substances are dissolved in water. 

 Some cannot dissolve in water and they 

 form what is called a suspension. (Raw 

 white of &^^ is a good example of a 

 suspension.) 



The important fact about protoplasm 

 is that it seems to have a very definite 

 and complicated structure and it keeps 

 this same structure, in general, as long 

 as it remains alive. High or very low 

 temperatures, dryness, or other changes 

 in the surroundings, of course, may kill 

 it. 



Of what is protoplasm composed? 1 he 

 studv of substances, their composition 

 or make-up, is called chemistry. To find 



Things Are Basically Alike unit ii 



Fig. 142 The 12 most common elements in plant 

 and animal protoplast)!. Calcium (Ca), sodium 

 (Na), and chlomie (CI) are not always present. 

 Symbols are explained at the bottom of this 

 cohnmi. Which fojtr elemefits are present in the 

 largest anioimts? What proportion of proto- 

 plas?n is oxygen? Percentages are calculated by 

 weight. 



out what substances make up protoplasm 

 biologists have used the methods devel- 

 oped by chemists for their own experi- 

 ments. For example, protoplasm has been 

 treated with chemical substances, and 

 many other types of experiments have 

 been performed. 



Among the first things learned was 

 what elements are present in protoplasm. 

 An element, you may remember, is one 

 of about 98 relatively simple substances 

 of which all other substances in nature 

 are made. Everything in our world, liv- 

 ing and lifeless, consists of one or more 

 of these elements. The elements are often 

 represented by symbols \\ hich are abbre- 

 viations either of the present name or of 

 some name used in the past. Perhaps you 

 already know that the symbol for oxy- 

 gen is O and that for iron is Fe. The 

 following elements are found in all pro- 

 toplasm: carbon (C), oxygen (O), ni- 

 trogen (N), hydrogen (H), sulfur (S), 



