128 Living Things Are Basically Alike unit ii 



9. Do gases move about? Fill a small bottle with oxygen. Cover with 

 a glass and stand on a table. Gently place a bottle of the same size, filled 

 with air, over the mouth of the bottle of oxygen after removing the glass 

 plate. Seal the mouths together with a strip of adhesive tape. Let stand 

 for 15 minutes. Remove the upper bottle without disturbing the lower. 

 At once thrust a glowing splint into the upper bottle. What do you 

 observe? What is lacking in this experiment? What else should you do? 



10. Diffusion of copper sulfate and of red ink. Drop a crystal of copper 

 sulfate into a tall jar of water and allow the jar to stand without dis- 

 turbing it. What happens within a day or two? Into the bottom of a 

 tumbler of water standing quietly on a table carefully place some red ink 

 with a medicine dropper. Do not stir the water. Record observations. 



11. Suppose three billion molecules of pure water are separated by 

 a membrane from a salt solution containing six billion molecules of water 

 and two billion molecules of salt. In which direction would the more 

 rapid diffusion of water through the membrane take place? Why? 



12. Remembering that fruits and vegetables are made up of large 

 numbers of cells with living membranes surrounding them, answer the 

 following: (a) How can you make sliced peaches juicy for serving? 

 (b) To freshen lettuce would you recommend fresh water or salt water? 



13. Does starch pass through a membrane? Boil some starch in water, 

 making a "starch paste." Fill the bulb of a thistle tube with this. Cover 

 with a membrane. Invert in a tumbler of water. Mark the level of the 

 licjuid in the thistle tube. After the experiment has been standing for 

 several hours, find out whether starch has passed through the membrane. 

 How can you do this? Has the liquid risen in the thistle tube? Write your 

 method, results, and explanations. 



Further Activities in Biology 



1. Can diffusion be speeded up by changing the concentration of water 

 in the thistle tube? Fill one tube with thick molasses (since this has much 

 sugar, the \\ater molecules are not concentrated). Fill another tube with 

 diluted molasses (there is little sugar so that the water molecules are more 

 concentrated). Set each in a jar of water. How soon can you see results 

 of diffusion in each tube? How much rise do you get in each? 



2. Set up an experiment to show that several substances can diffuse at 

 the same time. Use sugar and table salt. 



3. Will all kinds of membranes permit water and dissolved substances 

 to pass through? Set up experiments using membranes of rubber, cello- 

 phane, oiled silk, and so on. (^nrcfully record your results. 



4. Locy's Biology and Its Makers has interesting material on the early 

 history of the study of cells. Prepare a report. Singer's History of Livifig 

 Things ma)' be used also, or E. E. Snyder's Biology in the Making. 



