Stahl Biology
Respiration in Yeast Lab
Name- _____________________________________
Class Period-________________________________
Date- ____________________
Cellular respiration is the chemical process by which cells take
in oxygen and glucose (which are the products of photosynthesis)
and release carbon dioxide and water (which are the reactants of
photosynthesis). Cells accomplish this process by breaking down
nutrient rich molecules from the food that organisms eat to generate
ATP (Adenosine triphosphate), which is then used to fuel cellular
processes that require energy. All cells carry out the process of
cellular respiration in order to meet their energy needs for daily
survival both day and night.
This process originally starts in the cytoplasm via glycolysis,
which is an anaerobic process that breaks down the glucose
molecules into 2-3 carbon chains, turns them into pyruvic acid
(pyruvate), and produces 2 ATP. Remember that pyruvate is actually
made naturally in our bodies during metabolism when we digest
sugars and starches and is crucial for the Kreb’s Cycle / Citric Acid
Cycle to occur and to be successful in cellular respiration. After the
breakdown is complete, Coenzyme A bonds to the 2 carbon
molecule made from pyruvate and enters the Kreb’s Cycle in the
mitochondrial matrix and the process of making high energy
molecules continues.
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Chemical equation for Cellular Respiration
Yeasts are unicellular microorganisms of Kingdom Fungi. They
are a facultative anaerobe, which means that they can respire or
ferment depending upon environmental conditions. In the presence
of oxygen, respiration takes place (aerobic respiration). Without
oxygen present, fermentation occurs (anaerobic respiration). Both
processes require sugar to produce cellular energy.
Yeasts use sugar and warm water to grow. The warm water
provides heat to the yeast, resulting in an accelerated reaction. As
yeast grows it expands and gets bubbly, giving off carbon dioxide,
the same gas that your body exhales and plants absorb, and
produces ethanol. People use yeast to bake because the carbon
dioxide being released forms bubbles in the dough, causing the
dough to rise and expand. Since baking is done at high temperatures,
yeast ultimately dies and nearly all the ethanol evaporates. Ethanol
fermentation is used to produce alcoholic beverages. People also use
yeast fermentation to make ethanol for fuel (some information
obtained from University of Florida Science Outreach).
Chemical equation for Fermentation
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Objective: Students will use the respiration powers of yeast to blow
up a balloon. This activity will reinforce the basic principles of
respiration as a fundamental metabolic process for living organisms
using yeast as a model.
Pre-lab Questions:
1. Write the chemical equation for cellular respiration and label
the products and reactants.
2. Write the chemical equation for fermentation and label the
products and reactants.
3. In what organelle does cellular respiration take place?
4. Define aerobic and anaerobic respiration.
5. What is the function of the mitochondria?
6. What is the relationship between photosynthesis and cellular
respiration?
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7. What is glycolysis and where does it occur in the cell?
8. How many ATP does glycolysis produce?
9. What do you think is the importance of Coenzyme A? What is
the function of an enzyme?
10. What is a facultative anaerobe? Give an example.
Materials:
1 spoonful of dry yeast
1 Balloon
Warm Water
Recycled water bottle
2 Spoonfuls of Sugar
Masking Tape
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Tape Measure
Funnel
Measuring cup
Procedure 1:
1. Put 1 spoonful of yeast and 2 spoonfuls of sugar in the soda
bottle.
2. Fill the bottle ¾ full of warm water.
3. Quickly stretch the balloon over the opening of the bottle.
4. Seal with masking tape.
5. Shake the bottle to speed up the reaction.
6. Measure and record the diameter of the balloon every 5
minutes.
7. Shake as needed to mix the ingredients in between trials.
Procedure 2:
1. Place the bottom of a funnel into the opening of the balloon. You
may need to stretch the opening of the balloon a little bit so that it
fits.
2. Have a carefully supervised student pour 1 Tbsp. of yeast and 1
tsp. of sugar into the balloon through the funnel. Then fill the
measuring cup with warm water from the sink and carefully pour
the water into the balloon.
3. Remove the funnel from the opening of the balloon. Tie a knot in
the balloon to the water and yeast mixture inside. Measure the
diameter of the balloon every five minutes.
4. Record on the data table.
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Data Table:
Diameter of Balloon in 5 minute intervals
Time (minutes)
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Diameter (cm)
5
10
15
20
25
30
35
40
45
50
55
Data Analysis:
Make a Line Graph representing your data. Remember title &
labels.
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Post-Lab:
1. Explain the relationship between time and diameter that you
observed.
2. What was the gas that filled the balloon? Where did it come
from? Explain your answer.
3. What are the reactants in the observed reaction?
4. What are the products?
5. What is the purpose of warm water?
6. Why is respiration important for living organisms?
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