enzyme practical

Question 1

detailed method

Answer 1

-using a pen, draw an X on glass test tubes
-add10cm3 of milk powder solution to each test tube
-add 2cm3 of trypsin solution to 2cm3 of pH7 buffer in another set of test tubes
-stand all test tubes in water bath at 20 degrees for 10 mins
-add trypsin and buffer solution into milk powder solution test tube and mix thoroughly
-put tube back in water bath
-repeat using other test tubes
-time how long it takes for the milk to go clear by measuring time taken to see the X clearly
-record time for each three experiments, gather a mean
-repeat at different temperatures in 10 degree differences
-record data and draw bell curved graph

Question 2

what are the independent variables

Answer 2

temp
pH
enzyme conc
enzyme volume

Question 3

what are the dependent variables

Answer 3

rate of reaction
time taken for solution to turn clear

Question 4

why are the test tubes left in water baths for 10 mins before the trypsin and milk are added together

Answer 4

• to equilibrate temperatures for reaction to take place

Question 5

why do you wear safety goggles and gloves

Answer 5

• may have allergic reaction to enzymes
• avoid contact w eyes and skin
• also risk of burning yourself

Question 6

why did the milk become clearer

Answer 6

the enzyme trypsin breaks down (hydrolyses) the milk protein into smaller peptides, reducing the opacity of the milk, allowing more light to pass through

Question 7

explain use of buffer solution

Answer 7

to maintain constant pH

Question 8

describe and explain what you did to make sure the temperatures of water baths were reliable

Answer 8

measure temp of water bath throughout or at the start and then the end of reacting period

Question 9

why were three test tubes used per temperature investigation

Answer 9

enables calculation of a reliable mean
allows easy identification of anomalies

Question 10

A student decided to improve this investigation with control experiments. At each temperature she set up a test tube containing a solution of milk powder and buffer. She did not add trypsin. What would these control experiment show?

Answer 10

Controls show that the casein digested was due to the action of enzyme / not due to temperature changes

Question 11

It is difficult to decide when the milk solution goes clear. Suggest one better way of determining when the milk solution goes clear.

Answer 11

use a colorimeter, record time taken to reach a set value of absorbance

Question 12

drawbacks of this investigation

Answer 12

-lots of room for human error as the idea of clear colour is very subjective, some people will view ‘clear’ differently
-water temperature might be difficult to maintain temperature
-hard to know if solutions have been shaken the exact same to the same extent