PROBLEM I 



The C 07/1 posit ion of Living Things 



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o 



Fig. 145 Particles of sugar are shown as trian- 

 gles, particles of water as circles. According to 

 this picture does sugar water seem to be a coin- 

 pound or a mixture? Explain. 



understanding of what chemists mean 

 by a mixture. It differs from a compound. 

 Often when two or more elements are 

 put together they do not unite chemi- 

 cally. In this case they do not form a 

 compound. Instead they form a mixture. 

 In a mixture each element keeps its own 

 characteristics. In a compound where 

 chemical combination has taken place 

 the elements lose their special character- 

 istics. A4ixtures may be combinations of 

 compounds, or elements; or they may 

 be combinations of compounds and ele- 

 ments together. But the important thing 

 to remember is that the substances that 

 go into the mixture do not lose their 

 characteristics because they do not com- 

 bine chemically with one another. 



Protoplasm is a mixture of compounds 

 and elements, each substance retaining 

 its own special characteristics because 

 it does not combine chemically with the 

 other substances near it. To test your 

 understanding of the chemistry you have 

 learned, do Exercises 18 and 19. 



What have you learned? Let us review 

 all you have learned in this problem. 

 Plants and animals are made up of tinv 

 invisible structures known as cells. All 

 cells, normally, are alike in having three 

 parts: a cell body or cytoplasm, a nu- 

 cleus, and a cell membrane. These parts 

 are all living and can be called bv the 

 general term protoplasm. The nucleus 

 is denser protoplasm than the cell bod v. 

 It contains a substance called chromatin. 



But plant cells often have structures 

 which animal cells do not have. Almost 

 always they have a cell wall of a lifeless 

 material called cellulose. They usually 

 have one or more vacuoles filled with 

 liquid. And many of the cells in green 

 plants have chloroplasts which contain 

 the green coloring matter known as 

 chlorophyll. 



Protoplasm seems to be a thickish 

 liquid, colorless, and containing small 

 granules. Little is known about its struc ■ 

 ture, but we do know of what substances 

 it is composed. Chemists who study the 

 composition of substances define ele- 

 ments as comparatively simple substances 

 of which all other substances are com- 

 posed. They tell us that the elements 

 which regularly occur in protoplasm are 

 carbon, hydrogen, oxygen, nitrogen, sul- 

 fur, phosphorus, iron, potassium, and 

 magnesium. But these elements are for 

 the most part found united chemically 

 with each other in the form of com- 

 pounds. 



Some of the compounds found in pro- 

 toplasm, such as salt and other mineral 

 compounds, are found in nature outside 

 of living matter. But some of the com- 

 pounds found in protoplasm are never 

 found outside of living matter, except 



