ACTIVITY (1)

Aim
To show that microorganisms breathe

A) The effect of yeast on dough

Ingredients

1 cup of flour, 1/2 cup of warm water, 1 teaspoon of dried yeast, and 1 teaspoon of sugar

Step

1. All ingredients are mixed together to form dough.
2. The dough is then covered with a damp cloth.
3. The dough is left aside for 20 minutes.

Observation

The dough rises after 20 minutes.

At the beginning

At the end

 Conclusion

The yeast breathes, causing the dough to rise.

B) To show that yeast breathes

Aim

1. One teaspoon of sugar is mixed with some warm water in a conical flask.
2. Two teaspoons of dried yeast are then added to the mixture which is stirred with a spoon.
3. A ballon is fitted tightly over the mouth of the flask. It is then left aside in a warm place for 20 minutes.

Observation

At the beginning

After 20 minutes

1. Airbubbles can be seen forming in the flask.
2. The yeast gives off carbon dioxide which inflates the balloon.