How to tell when mealworms are out of breath
Materials List
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9" Pasteur pipette per group
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potassium hydroxide
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non-absorbent cotton
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electronic balance
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mortar and pestle
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food coloring
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mealworms
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vaseline
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masking tape
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metric rulers
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Petri dish/weighing tray
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forceps
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thin wooden applicator stick
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NOTE: POTASSIUM HYDROXIDE IS CAUSTIC AND WILL BURN SKIN AND EYES.
PROCEDURE
- Break up a few pellets of potassium hydroxide. Work quickly. KOH
will pick up water from the atmosphere and leave a residue on the
sides of the pipette that will burn the mealworm.
- Use forceps to place a few small pieces of KOH into the pipette.
Make sure all reach the constricted end of the tube. Wash and dry
forceps.
- Use the wood applicator stick to push a small amount of cotton into
the tube to cover the KOH.
- Choose a mealworm that will easily fit into the large end of the
pipette. Mass the mealworm and record the mass in grams.
- Place the mealworm into the tube tail first, being careful not to
injure it. Insert a cotton plug to hold the mealworm.
- Stick the large end of the pipette a short way into a jar of
vaseline to form a seal. The pipette is now a respirometer.
- Arrange the narrow tube end of the respirometer against the metric
ruler. Tape for stability.
- Wait one minute for temperature to stabilize.
- After the temperature has stabilized, apply a drop of food
coloring to the narrow pipette tip. Capillary action will suck the
drop in. Repeat if unsuccessful.
- After fifteen seconds record the position of the dye bubble on the
ruler. you may adjust the ruler so the bubble is at a convenient
starting point.
- Use a data table to record the distance traveded in mm by the
bubble each thirty seconds for a period of five minutes. If the bubble
does not move, check to see if the vaseline seal is broken.
- Repeat the trial two additional times. Dislodge the dye droplet by
holding the pipette by the large end and shaking gently.
- Using the data recorded, graph and explain the relationship
between mass (X axis) and average respiration rate (Y axis).
GROUP WORK AND DISCUSSION
- Determine the volume of oxygen used for each trial, then determine
the average volume of oxygen used in the three trials. Use the
formula V= pi r2h; h is the distance the bubble traveled. The narrow
end of the pipette usually has a diameter of around 1.0 mm.
- Could oxygen intake have been measure without the KOH? Explain.
- Discuss factors that affect the respiration rate of an organism.
- Describe a possible control for this experiment.
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What kinds of things do mealworms have in common with humans?
- What problems might the mealworm have in obtaining sufficient
oxygen by direct diffusion? What kind of a system do mealworms use to
distribute oxygen?
EXTENSION
Work with three respirometers to determine how environmental
temperature affects mealworm respiration. Determine respiration rate
at average room temperature (25 degrees Celsius) as above. Place one
pipette on an inverted aluminum pan filled with ice and repeat the
experiment, be sure to determine the temperature. Place another
pipette on a heating pad and repeat the experiment, again measuring
temperature.
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