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Cellular Respiration
Cellular Respiration

Learning Objectives

At the end of this lab, students should know...

Where does energy for living things come from?

Ultimately the source of energy for most living organisms is the sun. It is captured for use by the biosphere by photosynthetic organisms.

How does cellular respiration provide energy to organisms?

This process takes biomolecules, such as simple sugars like glucose and converts them into usable chemical energy in the form of ATP. Some forms use oxygen and others do not.

How can cellular respiration be measured?

By using a tool called a respirometer.

How does a respirometer work?

It measures the amount of oxygen being consumed by an organism. It uses KOH to trap the CO2 produced as the O2 is consumed. It is based on the ideal gas law.

What is the ideal gas law?

PV = nRT where P is absolute pressure, V is volume, n is the number of moles, R is the gas constant, and T is absolute temperature. The number of molecules of a gas thus can be calculated based on known temperature, volume, and pressure.

List of Materials

  • Tuberculin syringes
  • Capillary tubes
  • Metal washers
  • Seeds
  • Glass beads
    100 gm
  • Test tube racks
  • Timer
  • Marker
  • Ruler
  • Label tape
  • Soapy water
    200 ml
  • Red food color
    2 mL
  • 15% KOH
    20 mL
  • Absorbent cotton balls
  • Blade/Scissors
  • Hot glue gun
  • Water baths (minimum 2)
    Dependent on the lab size
  • Thermometer (minimum 2)
    Dependent on the lab size

Lab Prep

  1. Quantifying Respiration using Microrespirometers
    • To assemble the microrespirometers needed for the lab, first plug in the hot glue gun to preheat it.
    • Push the plunger of a tuberculin syringe all the way in and then cut the end off of the syringe.
    • Next, insert a capillary tube into the empty needle end of the syringe.
    • Push the capillary tube in until it touches the tip of the plunger.
    • Use the hot glue gun to create an airtight seal between the capillary tube and the tuberculin syringe. Make sure that the capillary tube is standing straight up while the glue dries.
    • Once the glue has dried, pull back on the plunger and make sure the capillary tube is not plugged.
    • Next, prepare the manometer fluid by adding red food coloring to soapy water. NOTE: The detergent coats the inside of the capillary tube, preventing the manometer fluid from sticking during the experiment.
    • Insert the capillary tube into the manometer fluid and then pull the plunger on the syringe until the entire capillary tube has been filled.
    • Then, eject the manometer fluid back out of the microrespirometer.
    • With a small piece of absorbent cotton, plug the barrel of the microrespirometer, inserting it into the syringe up to the 0 mL mark. Pack the cotton using a spare capillary tube or a glass disposable pipette.
    • Add a single drop of 15% KOH to the cotton using a spare capillary tube or a glass disposable pipette.
    • Add some nonabsorbent cotton to the KOH saturated cotton to act as a barrier to the seeds. Pack the cotton using a disposable pipette. The cotton should reach halfway between the 0 mL and 1 mL mark.
    • Reinsert the plunger carefully until it reaches the cotton and then remove any excess KOH by pressing it out.
    • Set four microrespirometers at each lab station.
    • Then, place a lab marker and two small dishes containing the seeds and glass beads for each group alongside the microrespirometers.
    • Finally, prepare two water baths by filling them with roughly 6 inches of water. The water level in the bath should comfortably fit two respirometers with the entirety of their two capillary tubes exposed.
    • Replace the lids and insert a thermometer in each bath to monitor the temperature. One bath should be set at about 25 °C, and the other at approximately 40 °C.


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