Respiration + gas exchange
Activitie 11.3 ( book page 143)
A1: It is important to boil water so that any dissolve 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.
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 yeast (alive) respire carbon dioxide and the limewater absorbed it. In the apparatus B the limewater solution remained clear, showing that the yeast (dead because 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 respire (anaerobically) and this process produces is characterized by the production ethanol as a result