Name(full)____________________________________________________________________________Date __________________Period_____
Hands on Kingdom Fungus: Yeast and Respiration Experiments
To obtain energy for life, all cells must carry out a process called respiration. You will be exploring respiration
and how it relates to the carbon cycle using a member of Kingdom Fungi: yeast. Kingdom Fungi is incredibly
diverse. Today, we will explore one of its smallest members: yeast are microscopic organisms that may be used
to model respiration rates in more complex living organisms.
Carbon is a chemical element found in all organic molecules. Carbon is one of the main components of cells.
Organisms get energy from carbon compounds, which they obtain from their environment. Plants use the sun’s
energy to synthesize carbohydrates from carbon dioxide and water. Animals get carbohydrates by eating plants
or by eating organisms that ate plants.
So, what do organisms do with carbon compounds? Through a process called cellular respiration, the cells of
most organisms use oxygen to release the energy that is stored in food molecules. Fungi, because they lack
chlorophyll, use a different process, called fermentation, which does not use oxygen to release energy. During
both cellular respiration and fermentation, energy is released when the chemical bonds that hold the food
molecules together are broken. All organisms then use elements such as carbon to build their own biological
molecules. The molecules left after these processes are waste products.
One of the waste products is carbon dioxide, a molecule that contains carbon. As organisms conduct cellular
respiration or fermentation, they release waste carbon dioxide as a gas into the atmosphere. Photosynthetic
organisms, such as plants, absorb this carbon dioxide and use it in photosynthesis. Through photosynthesis, the
carbon gets incorporated into parts of the plant (for example, as part of the starch in a potato) and may end up
being consumed by yet another animal. The constant cycling of carbon through organisms to the atmosphere
and back again is called the carbon cycle.
In this experiment, you will be working with yeast, a single-celled organism that is a fungus. Yeast obtains
energy from food through the process of fermentation. The experiment you will be first answering the question,
how does temperature affect the rate of yeast respiration?
You will follow-up with a new research question and lab that you will design.
Activity #1: Guided Experimentation
Research Question: How does temperature affect yeast respiration?
Your hypothesis:
Test your hypothesis:
1. Label each of the 5 bottles provided to your group.
2. Measure 15 (7) grams-1 packet of yeast into each cup.
3. Measure 20 (10) grams of sugar into each cup.
4. Mix yeast + sugar. You should now have 5 yeast and sugar mixtures.
5. Use a funnel to pour one yeast + sugar mixture into each of the 5 bottles.
6. Heat water in kettle provided.
7. Using the provided thermometers, measure out one cup-235ml (1/2 cup-118ml) of water at 20°C, 30°C,
40°C, 50°C, and 60°C.
8. Once all five cups of water are about the right temperature, use the funnel to add them to each of the five
bottles.
9. Immediately start your timer.
Data Collection
1. Make initial observations and write them down.
2. Every 5 minutes measure the foam that develops on top of the water in centimeters.
3. Stop measurements at 20 minutes.
Time
(Minutes)
Height of Foam in Centimeters
20°C
30°C
40°C
50°C
60°C
Start
(Initial)
5
10
15
20
Assign one person to keep track of time.
While you wait for measurements, answer questions 1-12.
Thinking About Respiration:
Essentially all living things require basic sugars to carry out respiration. Respiration creates energy for cells to
carry out important functions. For example, fungi cannot photosynthesize (make sugars using energy from
sunlight). Instead, they consume other organisms to get sugar for respiration. Whether eaten or created
through photosynthesis, these sugars are broken down and turned into energy for cells! In the process, they
produce waste products, including carbon dioxide gas, which the cells discard. Below, we will take a closer look
at photosynthesis and respiration to become familiar with these processes!
Respiration with Oxygen (Aerobic)
C6H12O6 + 6 O2 → 6 CO2 + 6 H2O + ATP
Glucose (sugar) + 6 Oxygen → 6 Carbon Dioxide + 6 Water + Adenosine Triphonsphate
1. What are the products of cellular respiration?
2. What substance from photosynthesis do cells use to respire? (Do you see the connection!?)
3. Why do cells respire? (What product of respiration is useful to the cell?)
When oxygen is not available, organisms may still carry out respiration to get energy for their cells. Respiration
without oxygen is called fermentation. Fermentation results in a new waste product. Can you find it?
Respiration without oxygen is what we will see yeast carry out today!
Respiration without Oxygen (Anaerobic)
Sugar → Carbon Dioxide + Alcohol + energy
C6H12O6 → C2H5OH + CO2 + ATP
4. Describe the above process including products and reactants
5. Describe where this type of respiration occurs and compare the amount of energy produce in this type
of respiration vs. Aerobic respiration.
6. Why do you think we use yeast to make bread? Explain.
7. Why do you think we use yeast to make wine?
Thinking Through the Scientific Process
8. In this experiment, why would measuring the height of the foam (bubbles full of a certain gas) tell us
about yeast’s respiration rates? Explain.
9.
What is a new research question for this type of experiment?
10. The independent variable (manipulated variable) for an experiment is the factor that you change on
purpose in an experiment. What is the independent variable for your experiment?
11. The dependent variable (responding variable) is the variable that may change as a result of a change in
the independent variable. The dependent variable is the data that is observed and measured in an
experiment. What is the dependent variable for this experiment?
12. In a controlled experiment (fair test) all other factors should be kept the same so that you can fairly
compare the results from the control group and the experimental group.
a. List three controlled variables - factors that were kept constant in both of the setups for this
experiment.
b. Does this experiment have a control group, if so describe, if not what should it be?
Results and Analysis
1. Once your data is collected, use graph paper to create a graph that clearly shows your results.
2. State one conclusion you can draw from your experiment.
3. Do your results support your hypothesis? Why or why not.
4. Break down the chemical formula for fermentation into its sources (left side of arrow) and its
byproducts (right side of arrow). What would you conclude is the source of the carbon in the carbon
dioxide byproduct?
5. Describe two specific things that you could have done to improve the reliability of this experiment.
6. Practical applications (2): Fully discussed.
7. Construct a diagram in the space provided below of the carbon cycle, in which you are one of the
organisms involved. Describe what is happening at each step. As a thought aid, think about a sugarbased food that you commonly eat, such as bread, and you become a part of the carbon cycle.
8. Analyze the combustion of gasoline that occurs in a car and answer the following questions: How is
burning gas in a car similar to digestion in living organisms? Sugar acts as a fuel for living organisms.
Gasoline, which comes from the remains of dead plants, provides the fuel for cars. In fact, with only 100
mL of gasoline, a typical automobile can travel approximately one kilometer (one thousand meters,
which is about five-eighths of a mile). Why is there so much stored energy in these fuels?