| Date | May 2015 | Marks available | 2 | Reference code | 15M.3.SL.TZ2.1 |
| Level | Standard level | Paper | Paper 3 | Time zone | Time zone 2 |
| Command term | Explain | Question number | 1 | Adapted from | N/A |
Question
Low protein diets are a widespread problem in the developing world. A low protein diet in a pregnant mother could affect a developing fetus. Other mammals are used as a biomedical model for energy metabolism and malnutrition in humans.
In an experiment to study the effect of protein levels in the diet, pregnant mammals were fed diets with different ratios of protein to carbohydrate:
• low protein : high carbohydrate (LP),
• adequate protein : adequate carbohydrate (AP),
• high protein : low carbohydrate (HP).
The table shows the average birth mass of the offspring and the body mass gain of the mother during the pregnancy. The concentration of several substances in the plasma of the mothers was also recorded. LDL (low density lipoprotein) is considered “bad cholesterol” and HDL (high density lipoprotein) is considered “good cholesterol”.
Identify the substance that varies the most in the plasma of the mothers.
Calculate the difference between birth mass of offspring whose mothers were fed the AP diet and the HP diet.
. . . . . . . . . . . . . . . . . . . . . kg
Distinguish between LDL cholesterol and HDL cholesterol in relation to the diet.
Explain the low birth mass of offspring born to mothers who were fed the LP diet.
In many societies doctors may recommend an HP diet for pregnant humans. Using the data, evaluate this recommendation.
Markscheme
urea
0.20 (kg) (less weight in HP)
LDL cholesterol increases and HDL cholesterol decreases as (proportion of) protein increases/carbohydrate decreases / OWTTE.
a. lack of essential amino acids to form protein;
b. not enough protein for growth;
c. not enough amino acids/protein to form muscle/tissues;
d. low protein may affect production of enzymes;
(the data does not support the recommendation):
a. as HP has the highest level of plasma urea which could be toxic;
b. HP has a high level of LDL/bad cholesterol and a low level of HDL/good cholesterol which could lead to coronary heart disease;
(accept high ratio of LDL: HDL)
c. HP produces a high level of glucose (compared to AP) which could lead to diabetes;
d. HP produces a low birth weight (compared to AP) which may affect development / OWTTE;
(the data does support the recommendation):
e. the mother has a similar weight gain to AP thus avoiding health problems;
Examiners report
N/A
N/A
This required the candidates to distinguish between LDL and HDL cholesterol. Many candidates failed to refer to the data in their answers so failed to score any marks.
N/A
The candidates were required to evaluate an HP diet for pregnant humans. Most candidates restated the data and gave no reasons for recommendations. As this was a 3 mark question it proved costly for many candidates. The question did discriminate well.
