Name: Hannah Collings-Myers

Date:November 1, 2023

Problem Statement: Suzie went to the gynecologist and she was diagnosed with a yeast infection. The
doctor told her that the normal pH of her vagina had been affected by her diabetes.Which pH condition is
most favorable for yeast growth?Does yeast prefer a particular substrate, if so, which substrate would
best promote yeast population growth?

Hypothesis: the growth of yeast will be optimal around pH 5-6 and certain sugar substrates such as
glucose and maltose will promote greater yeast growth compared to sucrose or fructose.

Aim: The aim of this laboratory experiment is to investigate the influence of pH levels and
various sugar substrates on the growth of Baker's yeast.

Apparatus and Materials:B aker’syeast (Saccharomyces cerevisiae) Various sugar substrates

(glucose, fructose, maltose, sucrose, etc.) pH buffer solutions (pH 4, 5, 6, 7, 8) Sterile water Test
tubes or conical tubes Graduated cylinder Hot Water bath or hot plate Timer

Method:

1)Weigh out 40 grams of each sugar (glucose, fructose, maltose, sucrose, etc.).Add
each sugar to 100 ml of sterile water in separate containers.

2)Stir or shake the solutions until the sugar is completely dissolved.

3)Label each container with the type of sugar and its concentration (40% w/v).

4)For each sugar solution, prepare a diluted solution at a concentration of 0.5% v/v. To
do this, transfer 0.5 ml of the 40% w/v sugar stock solution to a clean test tube.

5)Add sterile water to bring the final volume of the solution to 10 ml.Mix the solution
thoroughly by swirling.
6)Label a set of test tubes with the different sugar substrates and pH values being
tested.In each labeled test tube, add 5 ml of the diluted sugar solution prepared in step
2.

7)Using the appropriate pH buffer solutions (pH 4, 5, 6, 7, 8), adjust the pH of each test
tube to the desired level. Use a pH meter to confirm and adjust the pH levels if
necessary.

8)Add 1 ml of Baker’s yeast suspension to each test tube containing the sugar
solution.Mix gently by swirling the test tubes to ensure even distribution of yeast.

9)Place the labeled test tubes in a water bath or on a hot plate set to 30°C, which is the
optimal temperature for yeast growth and fermentation. Cover the test tubes to prevent
contamination and maintain a stable environment.

10)Using a graduated cylinder or other suitable method, measure the amount of carbon
dioxide (CO2) produced over time. Take measurements at regular intervals (e.g., every
30 minutes) to track the rate of CO2 production.

11)Record the amount of CO2 produced by each test tube at each time interval.Note
any observable changes in yeast growth, such as turbidity or gas production.Record any
variations in CO2 production based on the type of sugar substrate and pH level.

Variables:
Independent variable-Sugar substrates used.

Dependent variables- 1) Amount of Carbon Dioxide used.

 2) The growth rate of the bakers yeast.

Controlled variables-1) The volume of bakers yeast added to each test tube.
2) The concentration of sugar solutions.

Expected Results:It is expected t hat the growth of Baker's yeast will be optimal around pH 5-6 and
certain sugar substrates such as glucose and maltose will promote greater yeast growth compared to
sucrose or fructose.

Comparative Analysis Yeast Growth and Fermentation

Test tube pH level Sugar CO2 produced Yeast
number substrate (ml) growth rate

1 X-550

2 X-550

3 X-550

4 Y-210

5 Y-210

6 Y-210

Graph: Construct a graph of time vs yeast growth rate

Interpretation of results: Based on the data collected, the growth rates of bakers yeast can be compared
refers to the quantity of
among different sugar substrates.The amount of carbon dioxide produced
carbon dioxide gas generated as a byproduct of yeast fermentation. During
fermentation, yeast cells metabolize sugars, converting them into ethanol and carbon
dioxide through anaerobic respiration. measuring the amount of CO2 produced serves
as an indicator of yeast metabolic activity and fermentation efficiency. Higher levels of
CO2 production typically correspond to more vigorous fermentation and greater yeast
lgrowth.

Assumptions: 1) It is
assumed that the Baker's yeast used in the experiment exhibits relatively
uniform metabolic activity across different test conditions.
2) The experiment assumes that yeast cells fully metabolize the sugar substrates provided in the
culture medium, leading to complete fermentation

3) t
is assumed that the yeast cultures remain free from contamination by unwanted
microorganisms or foreign particles that could influence the experimental outcomes.

Precautions: 1) Handle yeast cultures with care to prevent spills and minimize exposure to the
environment

2) Wear safety equipment such as lab coats, gloves and goggles.

Contamination by unwanted microorganisms, such as bacteria or fungi, can

Sources of Error: 1)
affect the growth and metabolic activity of the yeast cultures.

2) Errors in measurement techniques, such as inaccuracies in volume measurements, pH

readings, or optical density readings, can affect the reliability of the data.

Limitations: 1)he choice of yeast strain used in the experiment may influence the observed
outcomes, as different yeast strains exhibit fermentation characteristics. So Findings derived
from one yeast strain may not necessarily generalize to other yeast strains or microbial
species, limiting the broader applicability of the results.

2)yeast growth and fermentation processes in industrial settings may occur over longer time
scales, influenced by gradual changes in environmental conditions, substrate availability, and
microbial interactions so the time frame may not be long enough to observe accurate results.