a day in sunshine, remove leaves and test for starch, as in No. 2 above. Describe 

 results. What do they show.? 



4 To demonstrate the liberation of oxygen during photosynthesis, place two 

 healthy potted plants under separate open-topped bell jars. Place a Hghted candle 

 in each bell jar and seal. After the candles are extinguished, allow the jars to cool 

 for about 10 minutes; then carefully Hft the stopper of each and insert a glowing 

 splint. After making sure that there is no longer sufficient oxygen within the bell 

 jars to keep a flame burning, place one jar in the dark and the other jar in the 

 light. After several hours of sunshine, test the air in both jars for oxygen. Com- 

 pare results and note conclusions, 



5 To demonstrate the relation of light to stoma movements, place one of 

 two similar potted plants in the dark and one in a sunny location. To the under 

 surfaces of a few leaves on each, apply benzine with a small paintbrush. If the 

 stomata are open, the benzine quickly penetrates to the inside, giving a transparent 

 appearance. If the stomata are closed, it takes longer for the benzine to penetrate. 

 Compare and note conclusions. 



6 To observe the closing of stomata through the microscope, peel the lower 

 epidermis from a leaf of a plant that has been exposed to direct sunlight for some 

 time. Place in water on a microscope slide. Apply a drop of concentrated sugar 

 solution to one edge of the cover-glass while watching a stoma through the micro- 

 scope; draw the sugar over the epidermis, by applying a bit of filter paper to the 

 opposite edge of the cover-glass. The sugar solution removes water from the 

 guard cells by osmosis. How do the guard cells react.? How would you explain 

 what happens? 



7 To show that osmotic pressure in the roots pushes liquid up, replace the 

 shoot of a plant with a glass tube. Cut the stem off a healthy potted plant about 

 an inch above the soil line; fasten a long glass tube to the stump by means of 

 rubber tubing. Tie the rubber tubing securely on the stem with a string. Stick a 

 similar glass tube in the soil. Keep the soil well watered. Compare results after 

 one or two days and account for the differences. 



QUESTIONS 



1 What are the sources of all organic materials? 



2 In the process of photosynthesis, what are the raw materials, what is the 

 source of energy, what by-products are given off, and what "machinery" is 

 essential ? 



3 What materials can both plant and animal cells synthesize from carbo- 

 hydrates ? 



4 What elements are present in protein substances? 



5 From the standpoint of food synthesis, what functions do the stems of 

 plants serve? 



6 How does girdling kill a tree? 



7 How are various forms of living things interrelated through the carbon 

 cycle? through the oxygen cycle? through the nitrogen cycle? 



8 In what respect is the soil a natural resource? 



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