Biology – Cellular Respiration
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Teacher Notes
Time: 45 minutes (plus 15 minutes for teacher preparation over two days)
Student Difficult: moderate
Purpose: Investigate cellular respiration in dormant and germinated seeds
Overview:
Students will compare the relative volume of oxygen used by dormant and germinated seeds. They will:
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prepare test-tube respirometers with dormant and germinated seeds
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measure the height of water that rises in the test tubes in response to the partial vacuum created by
oxygen being consumed
Lab Preparation:
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Use large, fresh seeds (peas or beans). Soak the seeds for 24–48 hours.
Lab Management:
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Remind students that respiration uses O2 and forms CO2. The pressure due to CO2 might cancel out any
change due to the take-up of O2. To solve this problem, potassium hydroxide is added to combine with
CO2 to form insoluble potassium carbonate.
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Do not to remove the tubes from the beaker while measuring water height.
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Students should measure the height of the water in the tubes after inverting them and again the next day.
Calculate any differences in height, if any.
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Setups should be stored at room temperature overnight.
Post-Lab Discussion:
Discuss the change in volume of gas in the tubes as indicative of the amount of O2 consumed. Ask, Why did
water move up into the tube? Water rises due to the partial vacuum created by oxygen consumption.
Answers: Analyze and Conclude
1) A bar graph is best; check students work.
2) Oxygen consumption was measured by the height of the water in the tubes. Water level in the tube with
germinated seeds was greater than that in the tube with dormant seeds. Dormant seeds respire very
slowly.
3) Tube 3 is a control. It may show a slight rise in water level due to atmospheric pressure changes.
4) The volume of gas and corresponding air pressure in the test tubes decreased with increasing cellular
respiration, that is, with increasing consumption of O2.
5) Water level would be higher after one day. After one week, the germinated seeds may die because there
is no CO2 in the tube for photosynthesis.
Cells and Energy
1
Overview of Cellular Respiration
Biology – Cellular Respiration
Neatly answer all questions completely for credit. Show all work.
Cellular Respiration
Plant cells use cellular respiration to make ATP from the sugars they produce during photosynthesis.
During cellular respiration, carbon dioxide (CO2) is formed as oxygen (O2) is used. In this experiment, you will
compare cellular respiration rates in dormant (dry) and germinated (pre-soaked) seeds.
Problem:
How do respiration rates compare in dormant and germinated seeds?
Process Skills:
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Measuring
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Graphing
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Collecting Data
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Analyzing Data
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3 test tubes
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marking pen
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6 pre-soaked seeds
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6 dry seeds
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6 cotton plugs
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1.5 teaspoons potassium hydroxide (KOH)
powder
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rubber band
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100-mL beaker
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25-mL colored water
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metric ruler
Materials:
Procedure:
1) Label the three test tubes as the following:
a. Tube 1: pre-soaked seeds; Tube 2: dry seeds; Tube 3: no seeds
2) Layer into the test tubes the following materials. Be sure that the layers of materials are compact, but
not too tight.
a. Tube 1: pre-soaked seeds, cotton plug, 1/2 tsp. potassium hydroxide, cotton plug
b. Tube 2: dry seeds, cotton plug, 1/2 tsp. potassium hydroxide, cotton plug
c. Tube 3: cotton plug, 1/2 tsp. potassium hydroxide, cotton plug
d. Caution: Potassium hydroxide is a strong base; avoid contact with eyes, skin, and clothing.
3) Use the rubber band to hold the three test tubes together.
4) Pour the 25 mL of colored water into the beaker.
Cells and Energy
2
Overview of Cellular Respiration
Name:
Class:
Date:
Biology – Cellular Respiration
Neatly answer all questions completely for credit. Show all work.
5) Invert the tubes and place them in the beaker as shown below. Wait 15 minutes.
6) Using a ruler, measure the distance (in cm) that the colored water travels up each of the three test tubes.
a. Record your results is the table below.
TABLE 1. CELLULAR RESPIRATION IN DORMANT AND GERMINATED SEEDS
Test Tube
Distance Colored Water Travels (cm)
1. pre-soaked seeds
2. dry seeds
3. no seeds
Cells and Energy
3
Overview of Cellular Respiration
Name:
Class:
Date:
Biology – Cellular Respiration
Neatly answer all questions completely for credit. Show all work.
Analyze and Conclude
1) Analyze Choose the type of graph that best represents the data. Construct your graph.
2) Analyze Describe your observations and measurements of test tubes 1 and 2. What do the data show?
Explain why differences between the two tubes might exist.
Cells and Energy
4
Overview of Cellular Respiration
Name:
Class:
Date:
Biology – Cellular Respiration
Neatly answer all questions completely for credit. Show all work.
3) Evaluate What is the function of test tube 3 in the experiment? What do the measurements from this
test tube demonstrate?
4) Infer Potassium hydroxide reacts with, and removes, carbon dioxide from the air. Why might cellular
respiration be responsible for water rising into some of the test tubes?
5) Apply Suppose this experiment were allowed to run an additional day. What might you expect to
encounter? What about after a week?
Cells and Energy
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Overview of Cellular Respiration