METABOLISM 135 



403. Is photosynthesis or respiration the more active process in a 

 normal green plant? How do you know this? 



404. Why is an excretory system, so necessary in animals, not needed 

 in the case of plants? 



405. State all the resemblances you can tliink of between an organism 

 and the flame of a candle. 



406. How is it possible for oxygen to get into a living cell? 



407. How do you think oxygen penetrates to cells deeply seated in 

 the plant body? 



408. Through what structures does oxygen enter (1) a young, grow- 

 ing root, (2) a leaf, (3) a woody twig, and (4) an old trunk? 



409. How do submersed water plants get their supply of oxygen? 



410. Plants which live in bogs or very wet places usually have large 

 air chambers in their tissues, particularly in roots or other subterranean 

 parts. Explain. 



411. Do you think that growing plants are good things to have in a 

 sick-room? Explain. 



412. If a plant were to be grown in air which had been freed of oxygen, 

 would it live longer in darkness or in light? Why? 



413. A seedling plant which has sprouted and grown in a dark place 

 will have a dry weight which is less than that of the seed from which 

 it grew, although the bulk of the seedling is far greater than that of the 

 seed. Explain. 



414. Does the increase in the dry weight of a plant measure the 

 amount of photosynthesis which has taken place in it? Explain. 



415. Which of three identical wooden posts will remain sound longest: 

 One left freely exposed to the air; one driven into the soil (as a fence 

 post), or one driven under water (as a pile)? Explain. 



416. Most of the fossils of animals and plants which have come down 

 to us were preserved in swamps rather than on high ground. Explain. 



417. Why is it necessary to change the water in an aquarium fre- 

 quently if animals are living in it alone, but infrequently, if at all, when 

 green plants are living in it alone? 



418. Where in a i)lant will you be likely to find the highest tempera- 

 ture? 



