This is my fifteenth science project. It is about yeast.

Objective: Observe how different temperatures affect the activity of enzymes in yeast.

Predictions:

I can list salt molecules, sugar molecules, acid molecules, base molecules, water molecules, CO2 molecules.

Salt molecules make food salty.

Acids turn cabbage juice pink.

Bases turn cabbage juice green.

Glue and starch are made of polymers.

I think that CO2 molecules make bread rise.

Observations: 

Make two batches of dough with one of the batches in a cold environment and the other in a warm environment. Observe the differences between them. 

Results:

The dough that was left in a warm place became light and airy.

The dough that was left in a cold place stayed flat and bubble-less.

There is a difference between the two doughs. One had Co2 bubbles and the other did not.

The difference between the doughs was that one of the doughs was colder than the other and did not have bubbles and the other dough was warmer and had bubbles.

Conclusion:

The enzymes in yeast made bread dough rise if the enzymes are warm. If they are too hot, the yeast will die and the bread will not rise. If they are too cold, the bread will not rise. To make bread rise, the enzymes cause fermentation of the sugar and make Co2 and alcohol. The Co2 makes the bread rise and the alcohol burns off when you bake the bread.