410 



PLANT METABOLISM 



Courtesy of Purdue University Agricultural Experiment Station. Reproduced 

 from Hiiuf/er Signs in Orops, a publication of the American Society of Agronomy 

 and the National Fertilizer Association, Washington, D. C. 



Fig. 15-10. Oats in Crosby silt loam of low fertility. Pot 16 (NPK), 

 treated with complete fertilizer, serves as check; plants healthy and vigor- 

 ous. Pot 13 (PK), nitrogen starvation; plants spindling, yellowish green, 

 slightly purplish stems. Pot 14 (NK), phosphorus starvation; plants dark 

 green, stems weak, slightly purplish tinged. Pot 15 (NP), potassium de- 

 ficiency; dark-green, weak plants, with oldest leaves brown and tip ends 

 deadened. 



REVIEW QUESTIONS ON PLANT METABOLISM 



1. What is the prime source of most of the energy used by man? 



2. Which process is of greatest importance in fixing carbon dioxide in the carbon 

 cycle of nature; of greatest importance in releasing carbon dioxide? 



3. How are photosynthesis and respiration interrelated? 



4. What are the chemical differences between chlorophyll a, chlorophyll b, proto- 

 chlorophyll, and bacteriochlorophyll? 



5. What is the evidence that all oxygen released in photosynthesis arises from 

 water? 



6. Describe a light reaction and a dark reaction in photosynthesis. How can they 

 be differentiated? 



7. Why is a quantum efficiency of 4 attractive from a theoretical standpoint? 

 Why is such a high efficiency questioned? 



8. What is the first demonstrable organic intermediate in photosynthesis? Which 

 products may it in turn yield? 



9. How does the plant synthesize starch? What is the difference between amylose 

 and amylopectin? 



10. Do plants require any preformed amino acids? 



11. Which are the most important sources of fixed nitrogen for maintaining the 

 nitrogen cycle in balance? 



