CP 7: Respiration

• What is the aim of the experiment described in the study material?

  To demonstrate that heat is produced by respiration
• What are the steps involved in the method of the experiment?

  1. Soak peas in water for 24 hours to germinate.
  2. Boil a second batch of peas to kill them.
  3. Wash both sets in a 1% bleach solution to disinfect.
  4. Rinse twice in distilled water.
  5. Place peas in inverted vacuum flasks with some air.
  6. Measure temperature at the start and end of the experiment.
• Why is it necessary to soak the peas in water for 24 hours?

  To allow them to start germinating
• What is the purpose of boiling the second batch of peas?

  To kill them
• What does the 1% bleach solution do to the peas?

  It acts as a disinfectant, killing any bacteria on the surface
• Why should the peas be rinsed twice in distilled water?

  To remove any traces of bleach
• What is the function of the inverted vacuum flask in the experiment?

  To insulate its contents and measure small temperature changes
• What happens to the carbon dioxide gas produced by the seeds during respiration?

  It escapes through the inverted flask and cotton wool
• What were the initial and final temperatures of the soaked peas?

  Both were 21°C
• What were the initial and final temperatures of the boiled peas?

  Initial: 21°C, Final: 24°C
• What conclusions can be drawn from the temperature results of the experiment?

  • Boiled peas showed an increase in temperature, indicating heat production.
  • Soaked peas did not show a temperature change, suggesting no respiration.
• Why is it necessary to kill any microorganisms on the surface of the peas?

  To prevent them from affecting the results of the experiment
• What is the importance of the flask containing dead peas?

  It serves as a control to compare with the germinating peas

  
• What is the temperature of the boiled peas at the end of the experiment?

  24°C
• What is the temperature of the soaked peas at the end of the experiment?

  21°C
• What is the temperature of the boiled peas at the start of the experiment?

  21°C
• What is the aim of the respiration investigation?

  To investigate the rate of respiration in living organisms using a simple respirometer.

  
• What is the temperature of the soaked peas at the start of the experiment?

  21°C
• What is the significance of measuring the temperature at the start and end of the experiment?

  To determine the heat produced by respiration
• What equipment is needed for the respiration investigation?

  • Small animal (e.g., maggots or germinating pea)
  • Simple respirometer
  • Soda lime
  • Ruler
  • Marker
  • Electronic balance
  • Pipette
  • Dye
  • Forceps
  • Water bath

  
• What factors were controlled in the experiment?

  • Mass of peas
  • Number of peas
  • Age of peas
• What are the controlled variables in the respiration experiment?

  • Mass of soda lime
  • Temperature
  • Time allowed for measuring
  • Change air in between repeats
• How can the effect of temperature on the rate of respiration be investigated?

  By repeating the set-up over a range of temperatures controlled by a water bath.
• What are some sources of error in the respiration experiment?

  Stress in captivity, insufficient acclimatization time, and air leaks in the apparatus.
• What is the method for setting up the respirometer?

  1. Put a known mass of soda lime into the boiling tube and cover with gauze.
  2. Weigh and place the organisms into the boiling tube.
  3. Use a pipette to place a drop of dye at the mouth of the capillary.
  4. Open the connection between the syringe and the respirometer.
  5. Leave the apparatus in a thermostatically controlled water bath for 5 minutes.
  6. Mark the starting point of the fluid.
  7. Close the tap and start the stop clock.
  8. Record the position of the fluid at one-minute intervals.
  9. Calculate the distance travelled by the dye per minute.

  10. Repeat the procedure at least 3 times and take a mean.

  11. Calculate the rate of respiration.
• What is the purpose of soda lime in the respirometer?

  To absorb carbon dioxide.
• How long should the apparatus be left in the water bath before starting the experiment?

  5 minutes.
• What should be done immediately after closing the tap on the respirometer?

  Start the stop clock immediately.
• How is the rate of respiration calculated?

  Rate of respiration = volume of oxygen consumed / mass of organism.
• What should be recorded at one-minute intervals during the experiment?

  The position of the fluid in the respirometer.