Required Practical 1 Flashcards
effect of pH on time taken by enzyme to hydrolyse starch
in this investigation, you were given buffers with a pH range from 5 to 8.
why?
- find optimum pH within range
- enzyme dentaured outside of this range
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?
- more kinetic energy
- more ES-C
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?
- compare with colour of iodine sol
- compare with previous reaction which had changed colour
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?
- end point qualitative
- temp could fluctuate
- no repeats
- vol of mixture not fixed
- vol of iodine not fixed
the student chose to join the points on the graph with straight lines rather than drawing a line of best fit.
suggest why?
- no intermediate values
- cannot predict between plotted values
describe a test you could have carried out to show products of starch hydrolysis are present?
- benedicts sol AND heat
- brick red colour indicates reducing sugar present
you used a buffer solution in your investigation.
what are buffer solutions used for?
maintain constant pH
you left the test tubes in water bath for 10 mins before you added the enzyme to the milk powder solution.
why?
to equilibriate temp at which reaction will take place
describe and explain what you did to make sure the temp of water baths were as relaible as poss?
- measure temp several times and add hot / cold water as appropiate
- to keep temp close to required temp
explain why you set up 3 experiments at each temp?
- identify anomalies
- calc more reliable mean
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?
- protein digested due to enzyme actions
the student concluded that the optimum temp for the enzyme was 40 degrees.
is the conclusion valid.
why?
- no
- 40 degrees only temp investigated
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?
- set up standard sol where complete digestion has occurred for comparison
- measure time take to reach same colour
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?
- liquid contains enzyme
- extra enzyme may affect reaction
describe how you would keep temp constant?
- place test tubes in hot water bath of required temp
- measure temp at regular intervals using thermometer
- add cold / hot water where appropiate
