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.
The size of the gas bubble on top of the small tube will change depending on: the gas produced by the yeast. How to measure the size of the Gas Bubble: Place the ruler next to the test tube and align the zero with the top of the test tube. Then read the value on the ruler at the position where the yeast suspension starts.