1. Write a prediction for this experiment with an explanation (3)
Correct identification of 2 variables with direction – As temperature increases time taken
for methylene blue to change colour will decrease and then increase (1)
As temperature increases to the optimum there will be more successful collisions
between dehydrogenase & the substrate so more H atoms will reduce methylene blue (1)
When the temperature increases above the optimum the dehydrogenase will denature
and will no longer carry hydrogen atoms to methylene blue so it will not be reduced (1)
2. List the following:
a. Independent variable and range (2)
Temperature of yeast incubation in °C (1)
Suitable range with 5 stated values with units (1)
b. Dependent variable (1)
Time taken for methylene blue to lose its colour in seconds (1)
c. Control variables (2)
Volume of yeast suspension used
Concentration of yeast suspension used
Volume of methylene blue used
Time for yeast to equilibriate
3. State what you will do as your control experiment (s) (2)
Boil the yeast to denature the dehydrogenase enzymes and then cool. (1)
Add water to methylene blue as opposed to the yeast (1)
All other conditions must remain the same, 2 listed; volume of yeast suspension used,
concentration of yeast suspension used, volume of methylene blue used (1)
4. Explain what you will do to make your results reliable (2)
The experiment will be repeated for each temperature 3 times (1)
A mean will then be calculated (1)
7. Construct a table (3)
Correct column headings in table (1)
Appropriate units in headings, not in body of table (1)
calc of mean/ rate as appropriate (1)
Correct identification of 2 variables with direction – As temperature increases time taken
for methylene blue to change colour will decrease and then increase (1)
As temperature increases to the optimum there will be more successful collisions
between dehydrogenase & the substrate so more H atoms will reduce methylene blue (1)
When the temperature increases above the optimum the dehydrogenase will denature
and will no longer carry hydrogen atoms to methylene blue so it will not be reduced (1)
2. List the following:
a. Independent variable and range (2)
Temperature of yeast incubation in °C (1)
Suitable range with 5 stated values with units (1)
b. Dependent variable (1)
Time taken for methylene blue to lose its colour in seconds (1)
c. Control variables (2)
Volume of yeast suspension used
Concentration of yeast suspension used
Volume of methylene blue used
Time for yeast to equilibriate
3. State what you will do as your control experiment (s) (2)
Boil the yeast to denature the dehydrogenase enzymes and then cool. (1)
Add water to methylene blue as opposed to the yeast (1)
All other conditions must remain the same, 2 listed; volume of yeast suspension used,
concentration of yeast suspension used, volume of methylene blue used (1)
4. Explain what you will do to make your results reliable (2)
The experiment will be repeated for each temperature 3 times (1)
A mean will then be calculated (1)
7. Construct a table (3)
Correct column headings in table (1)
Appropriate units in headings, not in body of table (1)
calc of mean/ rate as appropriate (1)
