Required Practical 9 - Respiration In Single Celled oraganisms

Question 1

Function of methylene blue in the practical

Answer 1

• a redox dye and acts as an alternate electron acceptor of the electrons transferred during ATP synthesis
• turns blue to colourless indicating the end

Question 2

method

Answer 2

1) set up water bath to 35C
2) add equal volumes of the yeast and glucose solution to 5 test tubes, place in water bath until the content reaches 35C
3) add 2cm3 of methylene blue to the test tubes, shake for 10 seconds, place back in the water bath and start timer
4) record how long it takes for the blue colour to disappear in the tube
5) repeat this for the other four test tubes
6) repeat for different temperatures

Question 3

how is the rate of respiration at each temperature calculated

Answer 3

rate = 1/time taken for methylene blue to decolourise

Question 4

why does the yeast solution need to be buffered

Answer 4

to maintain a constant pH so that the enzymes are functioning at there optimum pH

Question 5

what is the effect of temperature on the rate of respiration

Answer 5

• as temperature increase, the rate of respiration increases to an optimum
• as rate of enzyme activity increase

Question 6

explaining the results

Answer 6

• respiration reactions are controlled by enzymes
• as the temperature increases so does the kinetic energy so more enzyme substrate complexes are formed
• temperatures above the optimum will denature the enzyme
• rate of reaction will decrease/ stop

Question 7

rate of respiration

Answer 7

• it is affected by: temperature, O2 concentration, glucose concentration, ethanol concentration
• it is measured by the volume of CO2 produced