Question 23M.3.HL.TZ2.2
| Date | May 2023 | Marks available | [Maximum mark: 7] | Reference code | 23M.3.HL.TZ2.2 |
| Level | HL | Paper | 3 | Time zone | TZ2 |
| Command term | Deduce, Explain, Identify, Outline, State | Question number | 2 | Adapted from | N/A |
A study investigated the effect of pretreating egg white proteins with ultrasound on how they were digested by enzymes. A series of 10 % egg white solutions were exposed to ultrasound waves. Enzymatic hydrolysis of the egg whites with and without ultrasound pretreatment was then carried out using the enzyme alcalase in optimum conditions.
[Source: Material from: Stefanovic, A.B., Jovanovic, J.R., Grbavcˇic, S.Ž., Šekuljica, N.Ž., Manojlovic, V.B., Bugarski, B.M.
and Kneževic‑Jugovi, Z.D., Impact of ultrasound on egg white proteins as a pretreatment for functional hydrolysates
production, published 2014, European Food Research and Technology, reproduced with permission of SNCSC.]
State a variable that should be kept constant.
[1]
enzyme/substrate/egg white concentration/volume/pH/temperature;
Accept another reasonable variable.
The concept of control and independent variables appeared well understood by candidates.
Identify the independent variable.
[1]
(with/without) ultrasound pretreatment / time;
The concept of control and independent variables appeared well understood by candidates.
Outline the steps to produce a 10 % egg white solution.
[2]
- measure 10 g/parts egg whites;
- add to 90 g/parts of water;
Accept use of volume instead of mass.
Although most candidates understood that a 10% egg white solution required 10 parts (or equivalent units and multiples) egg white in 100 parts solution, many failed to recognize that 90 parts of water were required instead of 100 parts. A small number of candidates produced vague or irrelevant answers.
Each measurement was repeated several times. Explain the need for replicates of each treatment.
[2]
- more reliable results;
- to identify outliers/anomalous results
OR
reduce random errors; - assess the variability of the data
OR
allows statistical tests/calculation of mean/standard deviation/correlation;
Mp a: do not accept “accurate”.
The importance of using replicates for experimental reliability appeared well understood, although many candidates confuse accuracy, precision, and reliability. Elimination of outliers and to calculate statistical tests was included by
many.
Using the data, deduce whether pretreatment with ultrasound is effective for hydrolysing proteins.
[1]
it is not, as hydrolysis is higher without ultrasound pretreatment
OR
it is not, as hydrolysis is lower with ultrasound pretreatment;
Do not accept numerical values only with no attempt to evaluate their importance.
Do not accept increase/decrease instead of lower/higher.
Most candidates deduced that the ultrasound pretreatment was ineffective, but candidates sometimes failed to use the data to confirm it.