required practical 1

Question 1

what is required practical 1

Answer 1

to investigate the effect of a named variable on the rate of an enzyme controlled reaction

Question 2

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

Answer 2

• enzyme concentration
• substrate concentration
• temperature of solution
• pH of solution
• inhibitor concentration

Question 3

describe how temperature can be controlled

Answer 3

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

Question 4

describe how pH can be controlled

Answer 4

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

Question 5

why are enzymes and substrate solutions left in the water bath for 10 minutes before mixing

Answer 5

so the solutions can equilibrate and reach the temperature of the water bath

Question 6

describe a control experiment

Answer 6

• use denatured enzymes by boiling
• everything else can stay the same as the experiment

Question 7

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

Answer 7

• measure the time taken for the reaction to reach a set point eg. concentration ( rate of reaction = 1/time )
• measure concentration at regular intervals throughout the reaction: ploy on a graph with time on x axis 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 8

suggest a safety risk and explain how to reduce the risk

Answer 8

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

Question 9

explain why using a colorimeter to measure colour change is better than comparison to colour standards

Answer 9

it is not subjective and it is more accurate

Question 10

explain a procedure that could be used to stop each reaction

Answer 10

• boil to denature enzyme
• put in ice to lower kinetic energy so no E-S complexes form
• add high concentration of inhibitor so no E-S complexes form

Question 11

describe how processed data can be presented as a graph

Answer 11

• independent variable on the x axis and rate of reaction on y axis including units
• linear number sequence on axis with an appropriate scale
• plot coordinates accurately as crosses
• join point to point with straight lines if cannot be certain of intermediate values or draw smooth curve

Question 12

explain why the rate of reaction decreases over time throughout each experiment

Answer 12

• the initial rate is highest as substrate concentration is not limiting so many E-S complexes can form
• the reaction slows as the substrate is used up and often stops as there is no substrate left