24 PLANT BIOLOGY 



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1. Describe the preparation of the experiment. 



2. Examine the lime water inside the bell-jar. What proof 



have you that carbon dioxid has been absorbed ? 



3. Remove a leaf from each of the plants and test for starch. 



Tell what was done and state your observations. 

 Which leaf, therefore, contains starch? 



4. What is your conclusion as to the necessity of carbon 



dioxid for starch manufacture? 



5. What chemical elements that are present in starch might 



be furnished by the carbon dioxid (CO 2 ) ? 



6. The other raw material needed by plants for the manu- 



facture of starch is water (H 2 O) . What third chemical 

 element found in starch must be furnished by water? 



7. Now name the two raw materials used by plants in the 



manufacture of starch and state the chemical elements 

 which each can furnish. 



33. Manufacture of carbohydrates. The substance first 

 made by the combination of carbon, hydrogen, and oxygen 

 in the leaves is not starch, but a simple carbohydrate which 

 is then made into grape sugar. When the plant manufactures 

 more sugar than it needs for immediate use, the surplus is 

 changed to starch, and this is what we have found stored in 

 the leaves. 



34. Manufacture of proteins. We have already learned 

 that proteins contain carbon, hydrogen, oxygen, nitrogen, 

 and usually sulphur and phosphorus (see 21). The plant, 

 therefore, must somehow obtain these elements in order to 

 manufacture proteins. It has been proved that plants 

 manufacture sugar, and this probably supplies the necessary 

 carbon, hydrogen, and oxygen. The nitrogen that is needed 

 is furnished by compounds containing nitrogen such as salt- 

 peter (potassium nitrate, KNO 3 ), and the sulphur and phos- 

 phorus are secured from mineral compounds known as sul- 

 phates and phosphates. These compounds are derived from 

 soil water. From these compounds, namely, sugar and the 



