56 FERMENTATION AND RESPIRATION 



Exercise XI 



The rate of carbon dioxide production di- 

 vided by the rate of oxygen consumption is the 

 so-called respiratory quotient (R. Q.). What do 

 you find it to be? What does the equation for 

 the respiration of sugar, shown above, predict? 

 What would the R. Q. be if an organic acid 

 (e.g., palmitic acid, CisH.nCOOH) or an amino 

 acid were being respired rather than a sugar? 

 Can you conclude from your R. Q. what types 

 of metabolites are being respired by these pea 

 seedlings? 



Fermentation 



Working in pairs, stir about Ysofa yeast cake 

 into 20 drops (1 ml) of glucose solution in one of 

 the volumeter test tubes. The other tube, to 

 serve as thermobarometer, should contain 3 ml 

 of water. Adjust kerosene drops at the proximal 

 ends of the side-arms in the volumeter, and take 

 readings in both side-arms every minute, each 

 time subtracting the volume changes in the 

 thermobarometer from those in the experimental 

 tube. It may take a few minutes for a constant 

 rate of change to be established, since the sugar 

 solution must first be saturated with carbon 

 dioxide. 



Repeat this experiment, this time stirring the 

 yeast into 1 ml of galactose solution, to test the 

 ability of yeast to ferment this sugar. 



To verify that the gas produced in fermenta- 

 tion is carbon dioxide, make use of the fact that 

 carbon dioxide reacts with calcium hydroxide to 

 yield an insoluble precipitate of calcium carbon- 

 ate. Pour the yeast suspension in glucose solu- 

 tion from the volumeter test tube into a small test 

 tube, connect a gas-delivery tube, and let the gas 

 bubble through limewater (calcium hydroxide 

 solution; this is prepared by stirring powdered 

 calcium hydroxide in water for a few minutes, 

 and filtering). If the gas production is not rapid 

 enough, add more yeast and glucose to your 

 fermentation mixture. It may also take a little 

 time for the carbon dioxide produced to break 

 through the foam. 



Yeast ferments glucose, fructose, and mannose 

 indiscriminately. Why? Does it ferment galac- 

 tose? Why? It will help you to construct and 

 compare the molecular models of these sub- 

 stances. 



The total energy change in fermenting a mole 

 of glucose (how many grams?) to alcohol and 

 carbon dioxide is about 20 kcal. If this change 

 makes 2 moles of ~P available, what is its 

 efficiency in producing useful energy? 



Calculate the weights of carbon dioxide and 

 ethyl alcohol produced in fermenting one mole 

 of glucose. How do they compare? 



The total energy change in respiring one mole 

 of glucose is 672 kcal. If this produces 38 ~P, 

 what is its efficiency ? 



EQUIPMENT 



Per student 



2 wide test tubes 



microscope 



slide and cover slip 



Per 8 students 



4 test tubes, with assembly consisting of No. 



rubber stopper with 5-mm diameter hole; 2" piece 



of 6-mm diameter glass tubing 



4 volumeters 



4 gas-delivery tubes: 6" piece of rubber tubing Yg" 



in diameter and a 6"-long dropper tube 



2 dropping bottles of 10% glucose 



2 dropping bottles of 10% galactose 



2 250-ml beakers 



funnel 



filter paper 



cotton (nonabsorbent) 



soda lime 



calcium hydroxide 



cake of yeast 



pea seedlings 



