Required Practical 9: Respiration In Single Celled Organisms Flashcards
How is respiration measured within this experiment?
Respiration is measured using a redox indicator, specifically methylene blue
Respiration can be measured with a redox indicator dye, which one is used specifically in this experiment?
Methylene blue
What is the function of methylene blue in this practical?
It is a redox dye and acts as an alternate electron acceptor of the electrons transferred during ATP synthesis
It turns from blue to colourless, indicating the end point
Outline the procedure to investigate the effects of temperature on the rate of respiration of yeast:
- Set up a water bath at 35•C
- Add equal volumes of the yeast and glucose solution to four test tubes and place them in water bath to equilibrate
- Add 2cm cubed of methylene to test tubes and start timer. Shake for 10 seconds + place test tubes back in water bath. Record time takes for methylene blue to turn colourless for each test tube.
- Repeat experiment using temperatures of 40•C, 50•C, 60•C, 70•C
What is variable being investigated? Why is this variable being investigated?
Temperature is being investigated. This is because enzymes are affected by temperature. As temperatures increase, the kinetic energy also increases. This increases the likelihood of successful collisions between enzymes and substrates, leading to an increase in the rate of reaction
Beyond the optimum temperature, enzyme activity decreases as enzymes denature with high temperature
What is variable being investigated? Why is this variable being investigated?
This is done so the test tubes all arrive to the same temperature before the experiment. Also allowing the methylene blue and the yeast to also reach this equal temperature
Why should you not shake the test tubes?
By shaking the test tubes you might introduce oxygen to the tube, which will also act as an electron acceptor and reduce the validity of the experiment
Why does the yeast solution need to be buffered?
To maintain a constant pH so that the enzymes are functioning at their optimum pH
How are the results used to calculate the rate of respiration at each temperature?
Rate is calculated by 1/ mean time taken for methylene blue to decolourise
In seconds
What are possible limitations of this experiment? How can they be overcome?
Limitation: the end point is subjective for each test tube
Solution: By using a colorimeter quantitative results can be obtained
Limitation: there would be difficulty seeing colour change in the water bath and would lead to taking the test tubes to check on them - potential for temp drop
Solution: ideally having a see through thermostatic water bath
EXAM QUESTION 1:
A student investigated the rate of anaerobic respiration in yeast. She put 5g of yeast into a glucose solution and placed this mixture in the apparatus shown in the figure below. She then recorded the total volume of gas collected every 10 minutes for 1 hour
A) Explain why a layer of oil is required in this investigation
The oil being there could prevent the oxygen being taken up by the yeast.
EXAM QUESTION 2:
Calculate the rate of gas production in cm cubed g-1 min-1 during the first 40 minutes of this investigation. Show your working.
10 minutes = total volume of gas collected is 0.3cm cubed
20 minutes = total volume of gas collected is 0.9cm cubed
30 minutes = total volume of gas collected is 1.9cm cubed
40 minutes = total volume of gas collected is 3.1cm cubed
50 minutes = total volume of gas collected is 5.0cm cubed
60 minutes = total volume of gas collected is 5.2cm cubed
3.1÷ 5÷ 40 = 0.0155
