Question

How would you demonstrate that yeast can respire both aerobically and anaerobically?

Answer 1

Hint: Both anaerobic (fermentation) and aerobic breathing can be achieved by yeast. Both contain carbon dioxide, though a much smaller volume of ATP is released by fermentation. Ethanol is produced by fermentation.

Complete Answer:
For their life cycles, living creatures utilise energy produced by respiration. There are two forms of breathing: aerobic (which requires oxygen) and anaerobic (which requires no oxygen). In plant cells and certain microorganisms, anaerobic respiration also occurs. During fermentation and bread-making, anaerobic respiration of yeast is used:

glucose → ethanol + carbon dioxide

- Both aerobic and anaerobic respiration, yeast can breathe. It receives more energy than anaerobic respiration from aerobic breathing. It continues to breathe anaerobically in the absence of oxygen.
- The yeast begins first with aerobic respiration in bread-making. Carbon dioxide and water are created by it. This results in an increase in the dough.
- Then, in the absence of air, anaerobic respiration continues. When it breathes anaerobically, it generates ethanol. In fermentation, a net of 2ATP, ethanol and carbon dioxide is formed. 36-38 ATP, water and carbon dioxide are provided by aerobic respiration.

Note: The alcohol used in alcoholic beverages such wine and beer is ethanol. In bread-preparation, carbon dioxide gas bubbles stretch the dough and make the bread flourish.