Respiration + Gas Exchange
Activity: 11.3 (book page 143)
A1: It is important to boil the water so that any dissolved air can be driven away.
A2: Sugar solution must be cooled before adding the yeast because otherwise the yeast will be cooled and it won’t respire(as the practical requires).
A3: Liquid paraffin is added to isolate the solution of yeast in sugar from the air.
A4: In apparatus A the limewater solution turned cloudy, showing that the (living) yeast respires carbon dioxide and the limewater absorbed it. In apparatus B the limewater solution remained clear, showing that the yeast (dead as it was cooked) did not respire and therefore the limewater did not change as it did not absorbe carbon dioxide.
A5: In the sugar solution containing living yeast I would expect to find ethanol at the end of the experiment as the yeast respired (anaerobically) and this process is characterized by the producuction of ethanol as a result.
Activity: 11.8 (book page 149)