RP 1 - effect of a named variable on the rate of enzyme controlled reaction

Question 1

Give examples of variables that could affect the rate of an enzyme controlled reaction

Answer 1

• enzyme conc / volume
• substrate conc / volume
• temp of solution
• pH of solution
• inhibitor conc

Question 2

EQ : Describe how temperature can be controlled (2)

Answer 2

• Use a thermostatically controlled water bath
• monitor using a thermometer at regular intervals and add hot water/ cold water if temperature fluctuates

Question 3

EQ : describe how PH can be controlled (2)

Answer 3

• use a buffer solution
• monitor using a pH meter at regular intervals

Question 4

EQ : why were enzyme and substrate solutions left in water baths for 10 mins before mixing (1)

Answer 4

So solutions equilibriate / reach the temp of the water bath

Question 5

EQ : Describe a control experiment (2)

Answer 5

• Use denatured enzymes
• Everything else same as experiment

Question 6

Describe how the rate of an enzyme controlled reaction can be measured

Answer 6

• measure time taken for reaction to reach a set point
  • rate of reaction = 1/time
• measure concentration / volume / mass / colour of substrate or product at regular intervals throughout reaction
  • plot on a graph with time on the x acid and whatever is being measured on the y axis
  • draw a tangent at t=0
  • initial rate of reaction = change in y / change in x

Question 7

EQ : Suggest a safety risk and explain how to reduce this risk (2)

Answer 7

• handling enzymes may cause an allergic reaction
• Avoid contact with skin by wearing gloves and eye protection

Question 8

EQ : explain why using a colorimeter to measure colour change is better than comparison to colour standards (2)

Answer 8

• not subjective
• more accurate

Question 9

EQ : explain a procedure that could be used to stop each reaction (1)

Answer 9

• Boil / add strong acid or alkali => denature enzyme
  • put in ice => lower kinetic energy so no enzyme substrate complexes form
  • add high conc of inhibitor => so no enzyme substrate complexes form

Question 10

Describe how processed data can be presented as a graph

Answer 10

1) label x axis with named independent variable and units , and y axis with rate of reaction and units
2) plot a linear scale on each axis that will allow the graphs to occupy over half available space
3) mark data points with crosses
4) join data points by straight lines if intermediate values are not known or draw a line / curve if best fit if there’s a clear trend

Question 11

Explain why the rate of reaction decreased over time throughout each experiment

Answer 11

• initial rate is highest as substrate conc not limiting / many enzyme substrate complexes form
• Reaction slows as substrate used up and often stops as there is no substrate left