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How to tell when mealworms are out of breath

Recommended by Dee Millard











Materials List

  • 9" Pasteur pipette per group

  • potassium hydroxide

  • non-absorbent cotton

  • electronic balance

  • mortar and pestle

  • food coloring

  • mealworms
  • vaseline

  • masking tape

  • metric rulers

  • Petri dish/weighing tray

  • forceps

  • thin wooden applicator stick

NOTE: POTASSIUM HYDROXIDE IS CAUSTIC AND WILL BURN SKIN AND EYES.

PROCEDURE

  1. 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.

  2. 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.

  3. Use the wood applicator stick to push a small amount of cotton into the tube to cover the KOH.

  4. Choose a mealworm that will easily fit into the large end of the pipette. Mass the mealworm and record the mass in grams.

  5. Place the mealworm into the tube tail first, being careful not to injure it. Insert a cotton plug to hold the mealworm.

  6. 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.

  7. Arrange the narrow tube end of the respirometer against the metric ruler. Tape for stability.

  8. Wait one minute for temperature to stabilize.

  9. 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.

  10. 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.

  11. 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.

  12. Repeat the trial two additional times. Dislodge the dye droplet by holding the pipette by the large end and shaking gently.

  13. Using the data recorded, graph and explain the relationship between mass (X axis) and average respiration rate (Y axis).

GROUP WORK AND DISCUSSION

  1. 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.

  2. Could oxygen intake have been measure without the KOH? Explain.

  3. Discuss factors that affect the respiration rate of an organism.

  4. Describe a possible control for this experiment.

  5. What kinds of things do mealworms have in common with humans?

  6. 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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