EFFECT OF SUBSTRATE CONCENTRATION ON THE RATE OF COAGULATION

Confounding Variables

1. Temperature2. Batch of milk3. pH4. Method of mixing5. Concentration and volume of chymosin solution6. End point7. Time interval which the endpoint is checked

Limitations of this experiment?1. Difficult to maintain temperature of 30 degree using mixing water method (use elec-

tric water bath)2. When test tube is taken out of beaker to check for end point, heat is lost to sur-

roundings and its temperature changes variably (use a bigger container)3. Time of equilibration is not the same (do each trial one by one)4. Time for coagulation is too fast, so higher percentage error (use lower temperature)5. 10 drops of chymosin may vary in volume (use measured amount of chymosin)6. Time intervals may not be long enough to be accurate in pinpointing the time the

milk coagulates (use shorter time intervals)7. End point is subjective (use different endpoint)8. Not reliable (repeat experiment at least 3 times and take the mean time)9. Time taken to put in 10 drops is slow, so reaction begins even before the set vol-

ume of chymosin is added (use measured volume of chymosin, add quickly into milk)

Precautions1. Pipette and syringes must be rinsed before use.2. Milk must equilibrate so that temperature is same as water bath.3. Milk and chymosin must be rotated so that they will mix properly.4. Water bath must be maintained at constant temperature.5. Read meniscus at eye level.

correlation but no causal link, may be affected by other factors

repeated readings-increases the reliability, identify the anomalies

line graph – continuous datadot to dot- not enough intermediate value, cannot predict the rate between the points same thing used, to enable comparison

s.d, no overlapping, the difference is real, general trend is true

valid when it is accurate and precise, only affected by independent variable,

measurements are accurate, results are reliable, data and conclusion are valid.

Tentative nature of conclusion, not sure in every case, applied only in the expt.

Subjective and objective, qualitative and quantitative.

EFFECT OF SUBSTRATE CONCENTRATION ON THE RATE OF COAGULATION

When Describing:Split the graphs into sections, defined by the x axis (and where possible y axis) values. Ex-plain what happens in each section.

When Explain:Use scientific knowledge! i.e:1. increase in concentration of H2O2, increase in number of particles of H2O2 per unit

volume2. HIgher chance of collisions between enzymes and substrate3. More enzyme-substrate complexes formed 4. Higher rate of reaction

Percentage change:

Final reading - initial reading x 100Initial reading

Test for Protein:Take sample, add equal volume of Biuret’s reagant, if protein is present turns purple.

Test for reducing sugar:Take a volume of sample, add equal volume of Bennedict’s reagant, heat in water bath for a couple of minutes. If reducing sugar is present, solution turns brick red.

How do you separate curd?:Filter, squeeze out, allow to evaporate

Why is better to use cow rennin produced by bacteria?:Rennin from bacteria can be produced in larger scalesREnnin from cow contains protease. This may break down curdsEthical issues: People may not buy cheese that is made by killing cows to obtain their ren-nin

What might be the result if a student compared both enzymes?Would be smiliar. They both have the same genetic code/DNA. So they would have the same primary sequence, and thus the same tertiary structure. Both would fit equally well with the substrate. Equal number of enzyme-substrate complexes are formed and rate of reaction should be the same.

Why could data be unreliable?Small sample spaceSubjective Other confounding variables are not controlled, so data is not valid. Lack of repeats

Accurate: Close to the true valuePrecise: Measurements with little spread about the mean (use instruments with better pre-cision)Reliable: Means results are consistent - can be repeated and always come out the sameValid: When the results are only affected by the independant variableConclusions are valid only if supported by reliable and valid data.

EFFECT OF SUBSTRATE CONCENTRATION ON THE RATE OF COAGULATION

Control Experiment - experiment which is set up to prove that only the independant vari-able is affecting the result.