To test this idea we can see whether it is possible to detect any rise in temperature and the production of carbon dioxide, when living organisms are kept away from a supply of oxygen.

Yeast grows rapidly if it is supplied with glucose in solution. Indeed, wild yeasts are normally found growing on the skins of fruits like grapes and apples, from which they derive their food supplies. Our immediate problem is to remove the oxygen from the glucose solution and yeast.

Arrange the apparatus as shown in fig. 12

1. You can remove dissolved oxygen from glucose solution by heating it for a minute, and then cooling it without shaking. Now put in some yeast; the supply of oxygen from the air can be cut off by pouring one centimetre layer of liquid paraffin on to the mixture.

2. If you wish to check that the oxygen has been removed from the mixture, add a few drops of diazine green (Janus Green B) solution to the yeast suspension before you pour the liquid paraffin (wax) over it. This blue dye turns pink when oxygen is in short supply around it.

3. Arrange for any gas produced by the yeast to escape through a wash bottle containing bicarbonate/indicator solution (or lime water). During the process of anaerobic respiration some amount of carbondioxide is released. The released carbondioxide passes through the tube and turns lime water milky. We can observe the change in the temperature also during this process out for yourself. You may prefer to carry out the "carbon dioxide production" part of the experiment on a smaller scale, using test tubes. If you do, then warm them to about 37o C in order to speed up the test.

What happens when a baker prepares a dough by mixing yeast in it?

Let us recall maida dough and yeast powder activity that you performed in class 8th in the chapter 'The story of microorganisms'. Why volume of the dough has increased? Which gas released in that reaction?

If yeast and sugar solution are left to stand without oxygen for some days, they develop a characteristic smell, caused by production of new compound called ethanol, which has been manufactured by the yeast from