EXERCISE 41 



Problem. How does a cell take in the water ? 



What to use. 1 Test tubes ; glass tubing ; thread or small rubber bands ; celloidin ; solu- 

 tions of cane sugar, grape sugar (or glucose), salt ; thin starch paste ; white of egg. 



What to do. Make an " artificial root hair " by pouring celloidin into a test tube until 

 about half full, then pouring back into the bottle slowly, turning the test tube all the while, 

 leaving a thin film lining. Blow into the tube to help evaporate the ether and alcohol in 

 the solution of celloidin ; when the film is dry, pour in a little water ; gently poke the edge 

 of the dried film and gently push it from the tube, being careful not to tear it. Place a 

 few drops of water between the film and the glass and slowly work the film free from 

 the test tube. Test the film for holes by blowing into it. 



Different members of the class fill their sacs with different solutions boiled-starch 

 solution, dense sugar solution, white of egg, etc. Gently tie a glass tube in the end 

 of the bag to serve as an indicator of changes inside the artificial root hair. 

 Place in a jar of water. 



Record. Fill in the following table : 



Questions. 1. Do all substances tried diffuse through the membrane? 



2. Do all diffuse at the same rate ? 



3. Do all substances absorb water from their surroundings ? 



4. What seems to determine the rate of absorption ? 

 NOTE. Diffusion of substances through a membrane is called osmosis. 



5. Where do you know diffusion of liquids to take place ? 



6. Where do you know osmosis to take place ? 



1 Since it is very difficult for us to study the actual workings of living cells directly, we shall use an "artificial root hair 

 the present. 



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