34 PLANT BIOLOGY 



a. Describe what was done. 



6. Is grape sugar present now? How do you know? 



c. What must have happened to produce this result? 



2. We have now proved that two different liquids have 



passed through the membrane. 



a. Name these two liquids. 



b. Which of these two liquids has passed through the mem- 



brane in the greater quantity ? How do you know ? 



c. Which of these two liquids is the thicker or denser ? 



d. By a great many experiments it has been proved that, 



when any two liquids of different density are sep- 

 arated by a plant or animal membrane, results sim- 

 ilar to those noted above follow. To this inter- 

 change of liquids is given the name osmosis. In this 

 process of osmosis, is the greater flow of liquid from 

 the less dense to the more dense, or from the more 

 dense to the less dense? 



e. Why did not the water rise in thistle tube No. 2 ? 



3. Do you conclude, therefore, that grape sugar will or will 



not pass through a membrane? 



46. Osmosis in living cells. Laboratory Study No. 24. 



Peel a potato and then cut several cross sections about 

 inch in thickness. Allow these sections to stand in the 

 air until they bend readily. Half fill 

 one tumbler with water and a second 

 tumbler with a strong solution of 

 sugar or salt. Place some of the 

 sections in each of the two tumblers 

 and leave them for several hours. 



1. Describe the preparation of this 



experiment. 



2. Remove a section of potato from 



FIG. S - Cells from a each f th R idg d fe d 



potato, showing cell- ^ *,, , 



walls, cell-sap, and them - Compare the change that 



starch grains of differ- has taken place in the rigidity or 



ent sizes. stiffness of the sections placed 



in the strong solution and those in the tap water. 



