EXERCISE 67 

 RESPIRATION 



Materials. Small potted plant or germinating seeds ; four 6-ounce, 

 wide-mouthed bottles with two-hole rubber stoppers ; limewater ; 

 caustic-soda solution ; respiration chamber, arranged with a bell-jar 

 and air-pump platform ; filter pump ; glass and rubber tubing. 

 Assemble apparatus as shown in the illustration. 



Directions for work. With the apparatus assembled as illus- 

 trated, place the plant or seeds in the respiration chamber (4) 

 and some caustic- 

 soda solution in the 

 first and second bot- 

 ties (land 2). Close 

 all bottles and the 

 respiration chamber 

 tightly and start the 

 filter pump. If air 

 does not bubble through the soda solutions, there must be leaks 

 in some of the connections. Go over the whole train and tighten 

 up all parts until air comes through steadily, as indicated by the 

 bubbles in the bottles. Wire the joints between rubber and 

 glass tubing if necessary. 



After air has been flowing steadily for several minutes place 

 limewater in bottles 3 and 5. Make sure again that the air 

 passes through the whole train of bottles. If a green plant is 

 used, darken the chamber containing it in order to prevent 

 photosynthesis, else the results of respiration and photosynthesis 

 may not be distinguishable. Bottles 1 and 2 should remove the 

 carbon dioxide from the incoming air, and bottle 3 show whether 

 this has been accomplished ; bottle 5 will show whether there 

 is any carbon dioxide in the outgoing air. 



Does a plant give off carbon dioxide ? 



References 



BKKGEN and CALDWELL. Practical Botany, pp. 19, 76. 

 BERGEN and CALDWELL. Introduction to Botany, pp. 46-47. 



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