Respiration In Single Celled Organisms RP9

Question 1

What is this practical called?

Answer 1

The investigation into the effect of a named variable on the rate of respiration on cultures of single celled organisms

Question 2

What is the function of methylene blue in this practical?

Answer 2

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

Question 3

Outline the procedure to investigate the effects of temperature on the rate of respiration of yeast:

Answer 3

1. Set up a water bath at 35•C
2. Add equal volumes of the yeast and glucose solution to four test tubes and place them in water bath to equilibrate
3. 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.
4. Repeat experiment using temperatures of 40•C, 50•C, 60•C, 70•C

Question 4

How are the results used to calculate the rate of respiration at each temperature?

Answer 4

Rate is calculated by 1/time taken for methylene blue to decolourise

In seconds

Question 5

Why does the yeast solution need to be buffered?

Answer 5

To maintain a constant pH so that the enzymes are functioning at their optimum pH

Question 6

What is variable being investigated? Why is this variable being investigated?

Answer 6

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

Question 7

What are possible limitations of this experiment? How can they be overcome?

Answer 7

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