Like all batteries, eventually it gets depleted and needs to be replaced; this can be expected to happen after 5-10 years, depending on system usage. CMOS checksum error (and similar messages) or the system clock being reset are classic signs of the battery having been depleted. The BIOS settings contain several system-critical values.
In order to grow, yeast need glucose (C 6 H 12 O 6) or sucrose (table sugar, C 12 H 22 O 11), water (H 2 O) and warm temperatures. As yeast digest sugar, they turn into alcohol. In the process they give off carbon dioxide (CO 2) gas. The alcohol dissolves in the water and the gas escapes into the air. Yeast is used to make bread.
Most baked products are leavened by the expansion of the batter or dough. Leavening results in baked products with a larger volume with an open, porous texture. The three major leavening gases are air, steam, and carbon dioxide gas. Other leavening agents include ethanol and ammonia gas. Ethanol, which is a by-product of yeast fermentation, has a leavening effect in yeast-leavened products such as bread and rolls when it vaporizes during baking in the oven.