9. Investigate factors affecting the rate of respiration using a respirometer.

Question 1

describe aerobic respiration.

Answer 1

Organisms that respire aerobically take in oxygen and release CO2. Carbon dioxide is formed by the decarboxylation of respiratory substrates in the link reaction and Krebs cycle. Oxygen acts as the final election acceptor in the ETC during oxidative phosphorylation.

Question 2

What is the purpose of Soda lime/ limewater in the apparatus?

Answer 2

The equation for respiration shows that the volume of oxygen taken in should be equal to the volume of CO2 released, therefore making it difficult to measure rate of respiration as the total gas volume does not change. To overcome this, respirometers use soda lime to absorb CO2, so that a change in the volume of gases can be observed.

Question 3

Why is liquid drawn along the tube towards the organisms?

Answer 3

As the gas volume in the tube decreases, the pressure in the tube also decreases. This leads to a pressure differential that draws liquid along the tube towards the organisms.

Question 4

How can the rate of respiration be determined?

Answer 4

By measuring distance moved by the liquid over time, the rate of respiration can be determined.

Question 5

What is the independent variable used in this investigation?

Answer 5

The ORGANISM that is respiring

Question 6

What is the dependent variable?

Answer 6

The distance moved by a drop of coloured liquid

rate of respiration

Question 7

What are the control variables in the investigation?

Answer 7

Temperature

Age, size, stage of development of organisms.

Question 8

Method:

Answer 8

1. Assemble respirometer.
2. Place a known mass of one type of organism into boiling tube and replace bung. Record the mass. Handle live organisms with care and avoid harming.
3. Place a drop of coloured fluid at the end of the glass tube using dropping pipette. Open connection between syringe and respirometer. Use the syringe to draw the fluid onto the scale at the end furthest from the respirometer.
4. Note start position of coloured fluid.
5. Close tap to isolate respirometer from atmosphere and the syringe and start stop clock immediately.
6. Note position of fluid at one minute intervals for 5 minutes.
7. Work out distance travelled by liquid during each minute. Record results in table. Include columns for mean rate of oxygen uptake during the 5 minutes and the mean rate per gram of organism.
8. After 5 minutes open connection to outside air. Repeat for different organism.

Question 9

Risk:

Answer 9

Corrosion from soda lime:

• wear eye protection
• do not touch the soda lime: use a spatula to position in the respirometer.
• do not inhale any dust

Pathogens from organism used:
-wash hands after handling organism.

Question 10

Analysis of results:

Answer 10

Convert distance moved by the liquid into the volume of oxygen used. Use formula for volume of a cylinder, where r= radius of the hole in the glass tube and h= distance moved.

Calculate mean rate of oxygen uptake during the 5 minutes, then divide by the mass of organisms used to find the mean rate per gram of organism. (mm3/min/g)

Collect mean results for the rate of oxygen uptake. Spreadsheet? Calculate overall mean for each organism. Calculate STANDARD DEVIATION.

Plot a suitable graph of results. Use range/ standard deviation to indicate precision of data.

Question 11

What factors could cause variability in results?

limitations

Answer 11

Temperature
amount of movement of organisms
age/stage of development of organisms
Low resolution of the manometer scale could cause uncertainty in readings.

Question 12

How could the limiting/ varying factors be overcome?

Answer 12

Temperature could be controlled using a water bath.

Organisms could be matched between groups for size or stage of development.

Question 13

In a control experiment with GLASS BEADS as the ‘organism’, what factors may cause the liquid in the control tube to move?

Answer 13

Towards the respirometer:

• decrease in temperature.
• increase in atmospheric pressure

Away from the respirometer:

• Increase in temperature
• decrease in atmospheric pressure

Question 14

How could a control be used to correct experimental data?

Answer 14

The movement towards the control respirometer could be subtracted from the results.

The movement away from the control respirometer could be added to results.

Question 15

How could the investigation be extended?

Answer 15

• Study the effect of changing TEMPERATURE on the rate of respiration of organisms.
• As respiration is an enzyme-controlled process, the rate of respiration should show a marked INCREASE as temperature increases.

Question 16

How could the anaerobic respiration of YEAST be investigated?

Answer 16

• Do not use SODA LIME.
• Yeast suspension placed at the bottom of the boiling tube, with another smaller tube entering the suspension and connected directly to the gas syringe or tube containing coloured liquid.
• A layer of oil should be placed over the yeast: this will prevent any oxygen entering the suspension.
• Yeast will quickly use up oxygen and begin respiring anaerobically.
• Yeast cells will release CO2 due to DECARBOXYLATION of pyruvate to ethanal during anaerobic respiration. This CO2 will then be collected by the gas syringe or cause the coloured liquid to move to the right.