Evals Essay example

1152 Words May 27th, 2013 5 Pages
Rate of Fermentation (How Yeast Get Energy)

Purpose: To study how the rate of fermentation by yeast cells is affected by the concentration of molasses. You will be using yeast cells (microscopic organisms) and molasses (a product of photosynthesis in sugar cane). You will measure the rate of fermentation by measuring how much carbon dioxide (CO2) is given off by the yeast cells over a certain period of time.

Materials

Goggles
6 test tubes (18mm x 150 mm, for example), rimless is best
6 test tubes (10mm x 75 mm, for example), rimless is best
50 mL graduated cylinder
Medium sized beaker (for waste)
Test tube rack
Metric rule
6 little squares of aluminum foil (about 4 cm by 4 cm)
100 mL beaker with 50
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Procedure

1. Number the 6 large test tubes 1-6. Put your lab group name on some masking tape and place the tape on your test tube rack.

2. Fill test tube one almost to the top with 25% molasses solution.

3. Measure 25 mL of molasses solution in the graduated cylinder. Add 25 mL of water; mix well.

4. Fill test tube two almost to the top with the solution from step 3.

5. Pour off all of the solution in the graduated cylinder except for 25 mL.

6. Add 25 mL of water to this remaining solution; mix well.

7. Fill test tube three with the solution from step 6.

8. Continue with this serial dilution until you have filled test tubes 1-5 with molasses solutions.

9. Fill test tube 6 almost to the top with plain water.

10. Shake the yeast suspension very well and add 10 drops of yeast to each of the 6 test tubes. Shake the yeast suspension each time before you add it to a test tube.

11. Mix the yeast and molasses solutions in each test tube. You can do this by holding your thumb over the mouth of the test tube and inverting a few times.

12. This step is the tricky (and sticky!) part. Working with each tube of solution one at a time, you will do the following: Take one of the small test tubes. Fill the small test tube up to the top with some of the solution that is in large test tube #1. Then holding the large tube in one hand and the small tube in the other hand; tip them slightly so that they are

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