146 All Food Is Made by Green Plants unit hi 



1 1 . What use is made of carbohydrates besides conversion into other 

 food compounds? Of what importance is oxidation to the plant? 



12. Define respiration. Where in the plant does it occur? What gas is 

 used up in respiration? What gas is produced? Explain \\ hv carbon 

 dioxide diffuses out of a green plant at night but oxygen diffuses out 

 in the daytime. 



13. To sum up, contrast respiration and photosynthesis as to gases used in 

 each process; gases produced in each; energy transformation in each. 



14. Review the work done for the plant by the leaf, showing that chloro- 

 phyll is essential for making foods and for obtaining energy. 



15. iMake the following applications of your knowledge: (a) What do 

 you recommend for taking out grass stains? (b) Why may leaf-eating 

 insects kill a tree? (c) How must celery plants be treated to make 

 them white? 



16. Why are green plants of such great importance to you? 



Exercises 



1. What is the structure of the epidermis of a leaf? Narcissus, trad- 

 escantia, or many other leaves may be used. With a scalpel and a pair of 

 forceps remove a bit of the epidermis from the lower surface. Mount in 

 a drop of water. Examine it under low power. Do you see the tiny open- 

 ings or stomata? Study the cells that enclose them. How do these cells 

 differ in shape from the other cells of the epidermis? How many of these 

 cells enclose a single stoma? What are they called? Are the stomata 

 always the same size? Explain. Draw a portion of the epidermis showing 

 all of the structures that were mentioned. Label. 



2. Are there more stomata in the upper or lower epidermis? Remove 

 small pieces of epidermis from the lower and upper surfaces of a leaf. 

 Examine each under low power. What differences do yo" note? Count 

 the stomata in the field of vision. How could you arrive at an estimate 

 of the number of stomata on each surface of the leaf? 



3. Do green plants make starch in the presence of light? Keep a gera- 

 nium or coleus plant in the dark for about one week. Then cover one leaf 

 with carbon paper, and set the plant in strong light for four or five hours. 

 Test the covered leaf and an uncovered leaf for starch. (Hint: boil the 

 leaves in water and extract the chlorophyll with hot alcohol; then test them 

 for starch by adding a weak iodine solution.) What do you find? How can 

 you explain it? 



4. How can you prove that the presence of chlorophyll is necessary 

 for carbohydrate synthesis? Eor this experiment you will need plants 

 with leaves partly green and partly white, such as green and wiiitc coleus, 

 silver leaf geranium, or variegated tradescantia. Place the plant in the sun- 

 light for several hours. Remove one or two leaves and test them for starch. 

 You must be sure to dissolve out the chlorophyll first. Docs this experi- 

 ment have a control? Would it be as good to use a leaf that is completely 



