Required Practical 1

Question 1

in this investigation, you were given buffers with a pH range from 5 to 8.

why?

Answer 1

• find optimum pH within range
• enzyme dentaured outside of this range

Question 2

you were told to carry out the reaction in a water bath at 30 degrees C, rather than room temp.

explain why the reaction would be faster at 30 degrees than at room temp?

Answer 2

• more kinetic energy
• more ES-C

Question 3

you were told to decide for yourself when the blue-black colour failed to appear.

what did you do to ensure your decision was consistent?

Answer 3

• compare with colour of iodine sol
• compare with previous reaction which had changed colour

Question 4

apart from deciding when the blue-black colour failed to appear, give 3 limitations of the method you used that could have affected the reliability of your results?

Answer 4

• end point qualitative
• temp could fluctuate
• no repeats
• vol of mixture not fixed
• vol of iodine not fixed

Question 5

the student chose to join the points on the graph with straight lines rather than drawing a line of best fit.

suggest why?

Answer 5

• no intermediate values
• cannot predict between plotted values

Question 6

describe a test you could have carried out to show products of starch hydrolysis are present?

Answer 6

• benedicts sol AND heat
• brick red colour indicates reducing sugar present

Question 7

you used a buffer solution in your investigation.

what are buffer solutions used for?

Answer 7

maintain constant pH

Question 8

you left the test tubes in water bath for 10 mins before you added the enzyme to the milk powder solution.

why?

Answer 8

to equilibriate temp at which reaction will take place

Question 9

describe and explain what you did to make sure the temp of water baths were as relaible as poss?

Answer 9

• measure temp several times and add hot / cold water as appropiate
• to keep temp close to required temp

Question 10

explain why you set up 3 experiments at each temp?

Answer 10

• identify anomalies
• calc more reliable mean

Question 11

a student decided to improve the investigation with control experiments.

at each temp she set up a test tube containing a solution of milk powder and buffer.

she did not add trypsin.

what would these control experiments show?

Answer 11

• protein digested due to enzyme actions

Question 12

the student concluded that the optimum temp for the enzyme was 40 degrees.

is the conclusion valid.

why?

Answer 12

• no
• 40 degrees only temp investigated

Question 13

it is difficult to decide when the sol of milk powder goes clear.

suggest one bettwe way of determining when the solution of milk powder goes clear?

Answer 13

• set up standard sol where complete digestion has occurred for comparison
• measure time take to reach same colour

Question 14

you were told to remove the card from catalase extract and shake off any surplus liquid.

explain why it is necessary to shake off surplus liquid?

Answer 14

• liquid contains enzyme
• extra enzyme may affect reaction

Question 15

describe how you would keep temp constant?

Answer 15

• place test tubes in hot water bath of required temp
• measure temp at regular intervals using thermometer
• add cold / hot water where appropiate

Question 16

how many repeats did you carry out at a conc of 100% hydrogen peroxide?

why?

Answer 16

• 3
• anomalies identified

Question 17

in this investigation, you found the time taken for the card to rise to the surface.

explaim why this is a valid measure of rate of reaction?

Answer 17

• oxygen makes card rise
• faster rate of reaction - greater amount of oxygen released
• faster rate of reaction - more oxygen on card
• faster rate of reaction - quicker card will rise to surface

Question 18

a student carried out a similar investigation to yours.

he decided to carry out repeats using the same piece of card in the same tube.

each time the card reached the surface, he immediately pushed it back down again.

he noticed that the card took longer to return to the surface each time.

explain why the card took longer to return to the surface?

Answer 18

• less enzyme on card
• less oxygen
• fewer ES-C