Ayudar

LABORATORY GUIDE No. 3. BIOLOGY THIRD PERIOD 6th grade 2011-2012

HOW DOES THE PRESENCE OF SUGAR OR SALT AFFECT THE ACTIVITY OF YEAST?

ABSTRACT During this laboratory practical we will studiedhow yeast, classified in the kingdom fungi, grows under different conditions. Yeast is made up of singled-celled organisms such as the species Saccharomyces cerevisiae, which multiplies rapidly whenfed with the appropriate nutrients in moist environments. This yeast species by fermentation converts carbohydrates to carbon dioxide which is used in baking to produce the light and fluffy texture inbread.

OBJECTIVE Determine the effect of salt and sugar on yeast growth.

MATERIALS 5 small plastic narrow-necked bottles 5 round balloons 5 plastic straws Dry powdered yeast Sugar Salt Warm water(40-45%) Marking pen Beaker Graduated cylinder Metric ruler String

PROCEDURE Determination of the effect of sugar and salt on yeast growth

1. Gently stretch each of the balloons so that theywill inflate easily 2. Using the marking pen, label the bottles A, B, C, D and E 3. Use a beaker to fill each bottle with the same amount of warm water

Caution: Glass is fragile. Handle the beakergently to avoid breakage.
4. Put 25 ml of salt into bottle B.

5. Put 25ml of sugar into bottles C and E 6. Put 50ml of sugar unto bottle D 7. Put 6ml of powdered yeast into bottle A, And stir themixture with a straw. Remove it and discard it. 8. Place a balloon over the opening of bottle A. Make sure that the balloon opening fits very tightly around the neck of the bottle 9. Add 6ml ofpowdered yeast into bottle B, C, and D. And place a balloon over the opening of each a balloon. 10. Place a balloon over bottles E without adding yeast 11. Place the bottles in a warm spot away from drafts.Every ten minutes for 40 minutes, measure the circumference of each balloon by placing a string around the balloon at its widest part. 12. Include your measurements in the data table.

EXPECTED...