238 ELEMENTARY SCIENCE 



that they utilize in this process, and store up in its products 

 in latent form, to be released again when these products 

 are oxidized. 



The protoplasm of green leaves produces a substance 

 which acts as the means whereby the needed sunlight is 

 absorbed. Evidently, then, it is this light-absorbing sub- 

 stance that makes the leaves look green. If the spectrum 

 of sunlight is examined after it has passed through a solu- 

 tion of this substance, dark bands are found in it; these 

 dark bands indicate what rays are absorbed by this sub- 

 stance; they show us just what are those rays of sunlight 

 upon which our food-supply depends. This light-absorb- 

 ing, green-appearing substance is called chlorophyll. It 

 occurs in all green parts of plants in units of structure 

 called chloroplasts, which are microscopic bodies com- 

 posed of protoplasm and the chlorophyll which the proto- 

 plasm secretes. These chloroplasts are, then, the real 

 organs of photosynthesis, and now you are in a position to 

 understand the scientific definition of this process, which 

 is as follows: 



Photosynthesis is the manufacture of carbohydrates by 

 chloroplasts in the presence and by the aid of sunlight, water 

 and carbon dioxide being used, and a surplus of oxygen being 

 given of. 



Passing upward on the diagram beyond photosynthesis, 

 we note the appearance of fats and proteins, the latter 

 involving the addition of a number of new elements. Fat 

 and protein formation do not require light, and may occur 

 in animals as well as in plants, but always carbohydrates 

 are necessary as a basis. All these processes are, of coi 

 expressions of the activity of the protoplasm. 



Oxidation of foods, involving the release of energy 



