Does Baker's yeast respire, grow or reproduce?

The yeast feeds on the sugars in the flour and other ingredients. In other words, yeast will feed on the starches in flour as well as any other sources of glucose in the dough and turning them into alcohol and carbon dioxide gas which causes air bubbles and rise in the dough. This process is also called fermentation and creates flavor in the bread.

During rising, the yeast divides and multiplies, producing more carbon dioxide. As long as there is ample air and food (carbohydrates) in the dough, the yeast will multiply until its activity is stopped by the oven’s heat.

If there is no foam in the bowl, the yeast is dead due to
1. The yeast was dead before you used it.
2. The water used was too cold or too hot.
3. Too much salt was added or added too early.
4. The dough was not punched down or stirred enough.

Yeast produces ATP via glycolysis normally, whose end result is pyruvate. Pyruvate gets converted via ethanol fermentation pathway to CO2 and NAD+ where NAD+ gets funneled back into the glycolysis process. This is where the CO2 is being released; the foam is the trapped CO2 in liquid bubbles. Reproduction is occurring as long as there are resources available, the bubbles aren't indicative of reproduction though.