104 PHOTOSYNTHESIS AND RESPIRATION. 



atmosphere are used by plants ? What differences in the constitution 

 of the atmosphere do plants bring about under different conditions? 



34. Describe and explain the various methods with which you are 

 acquainted by means of which air can be deprived of its oxygen. 



35. What changes in the composition of the air are brought about 

 (a) by green plants, (6) by animals ? At what stage of its life does a 

 plant behave in this respect like an animal ? Explain the phrase 

 "balance of nature." 



36. Plants both absorb and give out carbon dioxide. State precisely 

 the circumstances upon which each process depends. 



37. Give an account of the process of Respiration, and sketch ap- 

 paratus by which you can investigate the gaseous interchanges associ- 

 ated with it. What is the physiological importance of respiration ? 



38. How would you make an experiment to study the periodic 

 increase in weight of a growing plant ? Supposing determinations of 

 weight were made every three hours during a summer day and night, 

 and expressed by means of a curve, give the probable form of the curve. 



39. What is meant by a " starch print " ? How may it be prepared 

 and what conclusions as to the formation of starch can you draw 

 from it? 



40. Seedlings of Bean are cultivated severally under the following 

 conditions : (a) the absence of light, (b) the absence of oxygen, (c) the 

 absence of C0 2 . Describe the manner of their behaviour in each case. 



41. You have discovered starch in the tubers of potatoes ; sugar in 

 the roots of carrots ; and oil in the seeds of nuts. Were these reserve 

 substances actually made in the tubers, roots, and seeds, and if not, 

 where were they made, and how did they get to where you found 

 them ? 



