Biology Internal Assessment
Pranav Chandra N.V
Grade 10
Research Question
How does the concentration of a sugar solution effect the rate of respiration of yeast.
Aim
To understand how to concentration of a sugar solution effects the rate of respiration of yeast.
Personal Engagement
Baking has always been a fun activity for me to do. I often help my mother or
grandmother in the kitchen and make bagels for the rest of my family. During the pandemic,
baking has turned into a worldwide craze to combat boredom as well. However, a large part of
baking would be getting the right texture using yeast. I recently began to think about why we
add sugar before adding the yeast, and it led me to pursue this topic for this investigation.
Background Information
Baker’s or budding yeast (Saccharomyces cerevisiae) is a single celled eukaryotic
organism that is commonly used in many household applications like baking. Yeast has also
been helpful in many laboratory applications including the investigation of cell division as
yeast replicates similarly to human cells and the investigation of human genetics.
The common application of yeast in baking is to produce carbon dioxide from a sugar
solution. Yeast respirate anaerobically in order to produce carbon dioxide and ethanol(C2H5O).
The ethanol is primarily used in the production of alcoholic drinks like beer. The carbon dioxide
byproduct of yeast is important for bread making as yeast helps to introduce air bubbles into
the bread, creating the distinct texture of bread. The formula for the anaerobic respiration of
yeast is:
C6H12O6 → 2CO2 + 2C2H5O
Glucose → Carbon Dioxide + Ethanol
Yeast occurs naturally and thrives on almost every surface, and as such has been very
widely used for over 5000 years, dating back to ancient Egypt. There are over 1500 species of
yeast, out of which, Saccharomyces cerevisiae is the primary species of yeast used in the
production of bread, beer and wine.
For household usage, the primary type of yeast used is baker’s yeast, which comes in
packages that are sold commercially. This can be done because of intense processing in a
very sterile environment, where the raw yeast culture is first brought in, it is made into a
sludge, and then dried into small pellets in sterile air. The yeast is then vacuum packaged into
airtight bags in order to prevent the yeast from growing inside the bag.
In this experiment, I will be varying the concentration of the sugar solution in which
the yeast will dissolve into in order to understand how the glucose concentration effects the
rate of respiration of yeast.
Hypothesis
As the concentration of the sugar solution increases, the rate of respiration of yeast will
increase.
Variables
Variable
Concentration of Sugar
Solution
Rate of Respiration of
Yeast
External Temperature
Mass of yeast
Variable Type
Why it is Controlled How it is Controlled
Independent
-
-
Dependent
-
-
To ensure the
By doing the
surrounding
experiment in a closed
temperature does not
room
To ensure that the
By measuring the mass
Control
Control
concentration of yeast of yeast before adding
is constant
it to the sugar solution
To ensure that all the By setting a timer and
Time that yeast is left
in the solution
Control
yeast samples have the
stopping the
same amount of time experiment when the
to respire
time runs out.
Materials
•
Yeast
•
Water
•
Gas Syringe
•
Beaker
•
Funnel
•
Rubber Tube
•
Water
Safety Precautions
•
Do not taste or ingest the yeast.
•
Do not touch your face while handling the yeast
•
Wash your hands thoroughly before and after the experiment
•
Gloves should be worn while performing the experiment
Procedure
1. Measure 100ml of water into a pot and heat it up to 40℃.
2. Add 2 grams of sugar and add it to the water.
3. Stir the solution well until no more sugar remains suspended remains
4. Add 5 grams of yeast to the solution, cover it and connect it to the gas syringe and
immediately start the timer.
5. When the timer runs out, stop the timer and note down the volume of gas produced.
6. Repeat steps one to 5 for all masses from 4 grams to 18 grams.
7. To find the rate of respiration, take the volume of gas produced, and divide it by the
time in seconds.
Data Collection
Concentration of
Mass of Sugar / g Sugar Solution /
g/cm3
2
0.02
4
0.04
6
0.06
8
0.08
10
0.1
12
0.12
14
0.14
16
0.16
18
0.18
Rate of
Volume of gas
Respiration /
produced / cm3
cm3/s
Data Analysis
Rate of Respiration of Yeast / cm3/s
Rate of Respiration of Yeast
1
0.9
0.8
0.7
0.6
0.5
0.4
0.3
0.2
0.1
0
0
0
2
4
6
0
0
0
0
0
0
8
10
12
14
16
18
0
Mass of Sugar added g
Rate of Respiration of Yeast
Evaluation
Conclusion
Bibliography