PROBLEM 2. How Cclls Keep Alive 127 



Exercises 



1. The behavior of protoplasm. Protoplasm may be seen best in Chaos 

 chaos or in slime molds. Watch the protoplasm first under low, then under 

 high power. Do not use a bright light. How does it move? If it continues 

 to move in one direction note how long it takes to move across the field 

 of vision. Can you then estimate the speed of motion? Draw out a soft 

 glass rod to obtain a microneedle. Touch the edge of the protoplasm with 

 it. What happens? 



2. Motion of plant protoplasm. Mount the edge of a young leaf of an 

 elodea plant on a slide. Warm the slide in your hand. Examine under the 

 low power. Move the slide about until you see motion in a cell. What is 

 it that you see moving? Explain their motion. 



3. Turn to Exercise 10 on page 69. Make a note of and describe all 

 the activities shown by the paramecium or other protozoan. If you are 

 fortunate you may see it dividing into two. 



4. What is one striking property of oxygen? Prepare oxygen by heat- 

 ing a mixture of three parts of potassium chlorate and one part of man- 

 ganese dioxide. (Consult a chemistry or general science text.) Collect 

 several small bottles of the gas by displacing water. Into one bottle thrust 

 a burning splint. Heat some sulfur in a deflagrating spoon until it begins 

 to burn,'then put it into a bottle of oxygen. Into a third bottle put a strip 

 of burning magnesium held with forceps. Thrust a glowing stick of char- 

 coal into a fourth. Describe carefully what you saw in each case. WTiy 

 does each substance stop burning after a short time? 



5. Does the oxygen of the air support burning? Your teacher can 

 provide you with air from which oxygen has been removed. Thrust a 

 brightly burning taper into it. What happens? Why? How may your 

 teacher have removed the oxygen? 



6. When does the process of oxidation stop? Fasten a candle to a block 

 of wood. Float the block in a pan of limewater. Light the candle. Invert 

 a jar over it so that the mouth of the jar is under the limewater. Why 

 does the candle go out? What substances are produced by the burning 

 of a candle? Where do these substances go? Why does the limewater rise? 



7. To test your understanding answer the following: (a) How do the 

 various ways of extinguishing fires take into account the fact that burning 

 requires oxygen? {b) Can you suggest a chemical explanation of the fact 

 that substances like carbon dioxide and water do not burn? 



8. How can you show that oxidation is going on in your body? Breathe 

 out for a few minutes through a tube into a small bottle containing a 

 small amount of clear limewater. What do you note? Explain. Now shake 

 a similar bottle of limewater so that it is well mixed with the air in the 

 bottle. Why should this be done? What is the evidence from this experi- 

 ment that oxidation of a substance containing carbon took place in your 

 body? Can you think of any other evidence that oxidation takes place in 

 your body? 



