1. Respiration HSW
Look at the number of questions in the pack related to practical respiration!
23 marks: they like it nearly as much as anaerobic respiration!

2. Learning outcomes: HSW
Investigate the effect of a variable on the rate of respiration of an animal or microorganism;
Compare aerobic and anaerobic respiration in yeast.
Presentation, analysis and evaluation of quantitative data
Calculate rates of respiration
Plot graphs showing the effect of a variable on the rate of respiration
Evaluation of data collection strategies:
Identify and evaluate the limitations of measuring rates of respiration

3. You will need to collect the following activity sheets
Activity 10: Determining the respiration rate in maggots and germinating seeds using respirometers
Activity 11: Determining the respiratory quotient (RQ) of germinating seeds
Activity 13: To investigate the effect of the type of substrate on yeast respiration
Activity 14: The effect of temperature on yeast respiration
Activity 15: The effect of ethanol on yeast respiration
Activity 16: Comparing anaerobic and aerobic respiration

4. Respirometer
A respirometer records the uptake of oxygen if the carbon dioxide has been removed.
The rate of respiration is indicated by the rate of oxygen uptake.
Look at equipment how is it going to work?

6. Why does the liquid move?
Respirometer
Sodium/Potassium/hydroxide absorbs all CO2 from the air in the apparatus from the beginning.
Why does the liquid move?
Oxygen molecules are absorbed by the organism and used in respiration.
The same number of carbon dioxide molecules are released but these are absorbed by the soda lime.(KOH)
This reduces the pressure inside the test tube (fewer molecules = lower pressure).
Atmospheric pressure pushes the liquid along the tube,(towards the tube) until the pressure in and outside the tube is equal.
Oxygen is the final electron acceptor, and it eventually combines with hydrogen to make water.
The carbon dioxide comes from the carbon dioxide released in the link reaction and the Krebs cycle as the carbohydrate is broken down.

7. Respirometer
As O² is consumed, the overall gas volume in the respirometer decreases, and this change can be used to determine the rate of cellular respiration.

8. Calculating the rate of respiration
Volume of a cylinder
Calculating the rate of respiration
If your tube does not have volumes marked onto it you will need to convert the distance moved into volume of oxygen used.
r=radius
h=height
pi 𝜋 =3.142
So area of cylinder cross section x length of bubble produced= volume of oxygen used in stated time
Then you would convert to rate per minute (divide)

9. Questions: What will be your control?
What are your control variables and why?
Suggest why a mean range of oxygen uptake readings should be taken?
Suggest what could be done to reduce the range of results, making the results more precise.

10. Control: Your control could be a second tube, but no organisms
Control variables are needed because in your control the following could happen:
Movement of the liquid towards the respirometer: drop in temp inside tube/increased atmospheric pressure
Movement of the liquid away from respirometer: increase in temperature inside tube/ decreased atmospheric pressure
A mean range of readings should be taken because: organisms have different metabolic rates, there may be different temperatures, difficult to obtain the same mass of organisms, organisms may have been left for different times before starting to take readings.
So to reduce the range of results and make them more precise: use similar organisms: same size and age, place respirometers into a water bath to maintain temperature, standard equilibration time

11. Respiratory rate
Faster or slower
Maggots or Mung beans
Why??

12. RQ
RQ becomes less meaningful if the living material is respiring anaerobically. If little or no oxygen is taken in, the RQ tends to infinity.
Many germinating seeds are known to respire anaerobically and so their RQs will depend on the type of respiration as well as the substrates respired.
The greater the fraction of anaerobic respiration, the larger the RQ will become

13. Activity 10: Demo Read and explain what you are setting up and why
Will take class readings of the movement of the bubble every 5 minutes for 40 minutes
Then:
Answer those questions you can at the bottom of the sheet (1,3,4,5)

14. Determining the respiratory quotient of germinating seeds
Activity 11
Determining the respiratory quotient of germinating seeds
What is RQ??
A measure of the ration of carbon dioxide produced by an organism to the oxygen consumed over a given time period
What can it tell us?
RQ can determine the respiratory substrate used
What figure are you looking for if carbohydrates, proteins or fats?
C=RQ=1, P=RQ=0.9, F=RQ=0.7
What would be a normal RQ and why?
Closer to 0.8 because a mixture of substrates is usually respired

15. Activity 11 Read and understand what you would be setting up and why
Answer questions 1-4
Now apply to some exam questions….

16. Other exam questions
One way of measuring the rate of respiration is …12 marks
Other practice questions
The apparatus ..10 marks
The apparatus 9 marks
Below is..4 marks

17. Using small organisms the rate of aerobic respiration can be determined by measuring the uptake of oxygen using a respirometer
Place 5g of organism into the tube and replace the bung.
Introduce a drop of dye into the glass tube.
Open the connection (three-way tap) to the syringe and move the fluid to a convenient place on the pipette (i.e. towards the end of the scale that is furthest from the test tube).
Mark the starting position of the fluid on the pipette tube with a permanent OHT pen.
Isolate the respirometer by closing the connection to the syringe and the atmosphere and immediately start the stop clock.
Mark the position of the fluid on the pipette at 1 minute intervals for 5 minutes.
At the end of 5 minutes open the connection to the outside air.
Measure the distance travelled by the liquid during each minute (the distance from one mark to the next on your pipette).
If your tube does not have volumes marked onto it you will need to convert the distance moved into volume of oxygen used. (Remember the volume used = πr2 × distance moved, where r = the radius of the hole in the pipette.)
Record your results in a suitable table.
Calculate the mean rate of oxygen uptake during the 5 minutes.