500 



Our Surroundings 



Experiments to Show that Starch is Made in Green 

 Leaves in the Presence of Light. The following experiment 

 shows the necessity of light for photosynthesis. 



Cover with tinfoil or a cork 

 about one-eighth of the surface 

 of both sides of the middle part 

 of a green leaf growing on a 

 plant. Place the plant in bright 

 sunlight with this leaf arranged 

 so that the upper side will get 

 full illumination. Near the 

 close of the day, cut off the 

 'leaf. Remove the cover of tin- 

 foil or cork, boil the leaf in wa- 

 ter to soften the tissue, and then 

 place it in alcohol for a day to 



EXPERIMENT TO SHOW remove the coloring matter. 



PHOTOSYNTHESIS T7 . t1 . , ... , 



Starch is made only in the exposed part of Finally, test With iodine f OF 



a green leaf. starch. Observe in which part 



the presence of starch is indicated, and state your conclusion as to 

 the importance of light in the making of starch. 



The necessity of light for photosynthesis may also be shown 

 in the following way : Place a growing green plant, provided with 

 proper heat and moisture, in a dark room, and after a few hours 

 remove several leaves and test them for starch. After this, place 

 the plant in the sunlight for a few hours, and then remove 

 several leaves and test for starch as before. State your con- 

 clusion. 



Comparison of Respiration with Photosynthesis. Respi- 

 ration is a breaking-down process; photosynthesis is a building-up 

 process. 



In respiration oxygen is taken in by the plant, and carbon 

 dioxide excreted ; in photosynthesis carbon dioxide is taken in by 

 the plant, and oxygen is excreted. 



In respiration carbon dioxide is formed as the result of a 

 chemical change ; in photosynthesis starch and sugar are made as 

 a result of a chemical change. 



