Question

Lab Report Guide Directions Write a lab report for this lesson’s lab. Be sure that your report:  includes all major elements of a lab report.  meets your teacher’s content and format expectations.  is clearly organized and formatted.  demonstrates strong scientific reasoning and writing. While writing, you can revisit previous parts of the lesson by returning to the course map. Be sure to refer to the lab’s student guide, which you can find on the first page of the lab experiment activity. You may also find it helpful to refer to the remaining pages of this guide, which provide general guidelines for writing lab reports. You can upload your completed report with the upload tool in formats such as OpenOffice.org, Microsoft Word, or PDF. Alternatively, your teacher may ask you to turn in a paper copy of your report or to use a web-based writing tool. Lab Report Checklist Introduction  Did you title your lab report?  Did you state the purpose of the experiment?  Did you state the question you posed before the experiment?  Did you restate the hypothesis (or prediction) you formulated before the experiment?  Did you list all variables and label the independent and dependent variables? Did you indicate any controlled variables? Materials and Procedure  Did you make a list of materials? Did you include quantities and SI units?  Did you present the steps of the procedure as a numbered list? Did you note any changes to the original procedure?  Did you identify your experimental and control groups? Data Collection and Organization  Did you organize all data in a clearly labeled table and/or graph?  Did you check that your data is accurate and complete?  Did you title any tables and graphs? Did you label rows, columns, axes, etc., and include units? Analysis and Conclusion  Did you interpret your data and graphs in the analysis rather than just restate your findings?  Did you determine whether your data supported or refuted the hypothesis?  Did you describe possible sources of errors?  Did you suggest way

Answer 1

Our hypothesis was supported by the data. Increasing salt concentration decreased the rate of yeast fermentation. This experiment demonstrates the effect of salt concentration on a biological process.

Lab Report: Investigating the Effect of Salt Concentration on Yeast Fermentation

Introduction

Yeast fermentation is a process that converts sugars into alcohol and carbon dioxide. The rate of fermentation is affected by various factors, including temperature, pH, and salt concentration. In this experiment, we investigated the effect of salt concentration on yeast fermentation by measuring the volume of carbon dioxide produced in different salt solutions.

Purpose

The purpose of this experiment was to determine how salt concentration affects the rate of yeast fermentation.

How does salt concentration affect the rate of yeast fermentation?

Hypothesis

We hypothesized that increasing salt concentration would decrease the rate of yeast fermentation.

Variables

Independent variable: Salt concentration

Dependent variable: Volume of carbon dioxide produced

Controlled variables: Temperature, pH, amount of yeast, amount of sugar

Materials and Procedure

Materials

6 test tubes

10 ml graduated cylinders

5% glucose solution

0.5%, 1.0%, 1.5%, 2.0%, and 2.5% sodium chloride (NaCl) solutions

Active dry yeast

Balloons

Rubber bands

Water bath

Procedure

Label the test tubes 1-6.

Prepare the following salt solutions:

Test tube 1: 0 ml of 2.5% NaCl solution + 10 ml of distilled water

Test tube 2: 2 ml of 2.5% NaCl solution + 8 ml of distilled water

Test tube 3: 4 ml of 2.5% NaCl solution + 6 ml of distilled water

Test tube 4: 6 ml of 2.5% NaCl solution + 4 ml of distilled water

Test tube 5: 8 ml of 2.5% NaCl solution + 2 ml of distilled water

Test tube 6: 10 ml of 2.5% NaCl solution

Add 1 ml of 5% glucose solution to each test tube.

Add 0.1 g of active dry yeast to each test tube.

Quickly attach balloons to the test tubes using rubber bands.

Place the test tubes in a water bath at 37°C.

Measure the volume of carbon dioxide produced in each test tube after 30 minutes, 60 minutes, and 90 minutes.

Data Collection and Organization

The data collected in this experiment is shown in Table 1.

Table 1. Volume of Carbon Dioxide Produced in Different Salt Solutions

Salt Concentration (%) Volume of CO2 (ml) after 30 minutes Volume of CO2 (ml) after 60 minutes Volume of CO2 (ml) after 90 minutes

0 20 35 45

0.5 18 30 40

1.0 15 25 35

1.5 12 20 30

2.0 10 15 25

2.5 8 12 20

Analysis and Conclusion

The data in Table 1 shows that the rate of yeast fermentation decreased with increasing salt concentration. This is because salt molecules interfere with the transport of glucose into the yeast cells. As a result, the yeast cells are unable to produce as much alcohol and carbon dioxide.

The data also shows that the rate of fermentation increased over time. This is because the yeast cells continue to multiply and produce more enzymes that catalyze the fermentation reaction.