Respiration experiments

Question 1

What piece of equipment can be used to measure the respiratory rate?

Answer 1

Respirometer

Question 2

Describe how the equipment below can be used to measure the rate of anaerobic respiration of cells in a liquid culture e.g. yeast cells.

Answer 2

• The yeast suspension is placed in a chemical flask connected to a delivery tube, a bung is used to seal the flask, a layer of oil or paraffin is floated on top to prevent oxygen dissolving into the water. The delivery tube is connected to a gas syringe.
• Allow time for the oxygen to be absorbed/used to make conditions anaerobic
• As the yeast respires it releases CO2 which increases the volume of gas in the flask and syringe and pushes the plunger outwards
• The volume of carbon dioxide collected in the gas syringe after a period of time is recorded
• The rate of respiration is calculated using the equation rate = volume of gas
  Time
• The experiment is repeated in different conditions e.g. different temperatures/different respiratory substrates.

Question 3

Describe how the equipment below can be used to measure the rate of anaerobic respiration of cells in a liquid culture e.g. yeast cells.

Answer 3

• The yeast suspension is placed in a chemical flask connected to a delivery tube, a bung is used to seal the flask, a layer of oil or paraffin is floated on top to prevent oxygen dissolving into the water. The delivery tube delivers any gas produced through limewater
• Allow time for the oxygen to be absorbed/used to make conditions anaerobic
• As the yeast respires it releases CO2 which is bubbled through the limewater forming a precipitate.
• The precipitate is filtered away from the limewater and its mass measured
• The rate of respiration is calculated using the equation rate = mass of precipitate
  Time
  The experiment is repeated in different conditions e.g. different temperatures/different respiratory substrates.

Question 4

Describe how the equipment below can be used to measure the rate of anaerobic respiration of cells in a liquid culture e.g. yeast cells.

Answer 4

• The yeast suspension is placed in a chemical flask connected to a delivery tube, a bung is used to seal the flask, the delivery tube contains coloured ink, alkaline pyrogallol absorbs oxygen to make conditions anaerobic.
• Allow time for the oxygen to be absorbed/used to make conditions anaerobic
• As the yeast respires it releases CO2 which will increase the volume of gas in the flash and push the coloured ink to the right.
• The distance moved by the ink in a given time period is recorded
• The volume of gas release can be calculated if we know the radius of the delivery tube.
• The rate of respiration is calculated using the equation rate = volume of gas
  Time
• The experiment is repeated in different conditions e.g. different temperatures/different respiratory substrates.

Question 5

How can the method above be modified to measure the rate of aerobic respiration?

Answer 5

• Swap pyrogallol for sodium hydroxide to absorb carbon dioxide instead of oxygen
• The ink will move towards the right due to a reduction in the volume of gas inside the beaker as oxygen is used up.

Question 6

Describe how a redox indicator can be used to measure the rate of respiration of yeast cells in solution.

Answer 6

• A redox indicator like DCPIP or methylene blue can be used to indicate respiration occurring
• During respiration, electrons are transferred by redox reactions along the electron transport chain
• These chemicals accept electrons and become reduced. This changes their colour to colourless.
• The time taken to become colourless is recorded.
• Rate is then calculated using 1/time.

Question 7

Describe the principles of a simple respirometer that measures the rate of aerobic respiration of small organisms e.g. woodlice.

Answer 7

• Sodium hydroxide absorbs the CO2 released by the insect as it respires.
• The equipment is air tight so any oxygen used up will cause a pressure change inside the tubing
• The coloured liquid will move towards the animal
• The opposite side is a control test using glass beads of equal mass to the insect. This balances any changes in pressure caused by anything other than respiration of the insect.
• The volume of gas release can be calculated if we know the radius of the tube.
• The rate of respiration is calculated using the equation rate = volume of gas
  Time

Question 8

What chemical absorbs oxygen to make conditions anaerobic?

Answer 8

• Pyrogallol

Question 9

What chemical absorbs carbon dioxide?

Answer 9

• Sodium hydroxide/potassium hydroxide

Question 10

What chemical can be placed on top of a liquid suspensions of cells to prevent oxygen dissolving into the solution and hence causing anaerobic conditions (once all oxygen in the liquid has been used up)

Answer 10

• Oil/paraffin