Question 23M.2.SL.TZ2.1
| Date | May 2023 | Marks available | [Maximum mark: 12] | Reference code | 23M.2.SL.TZ2.1 |
| Level | SL | Paper | 2 | Time zone | TZ2 |
| Command term | Comment, Describe, Discuss, Distinguish, Estimate, Evaluate, State | Question number | 1 | Adapted from | N/A |
There is increasing interest in the bacteria that live in the human gut, known as the gut microbiota. Evidence is accumulating of widespread effects on human health, with some species of bacteria increasing the prevalence of specific diseases and others giving protection.
Long-term diet appears to influence the numbers and types of bacteria that are present in an individual’s gut. Several different characteristic combinations of bacteria (called enterotypes) have been discovered. The stacked column graph shows relative amounts of different genera of bacteria in the gut of people with four of these enterotypes. The Bacteroides 2 (B2) enterotype is associated with an increased prevalence of inflammatory bowel disease.
[Source: Material from: Vieira-Silva, S., Falony, G., Belda, E. et al., Statin therapy is associated with lower
prevalence of gut microbiota dysbiosis, published 2020, Nature, reproduced with permission of SNCSC.]
Using the data in the stacked column graph, describe the features that characterize the B2 enterotype.
[2]
- nearly half is Bacteroides / more Bacteroides (than other enterotypes);
- few Prevotella/fewer Prevotella than in P and R
OR
less Faecalibacterium than other enterotypes
OR
Ruminococcus is the lowest in B2; - only 40 % other taxa / fewer other taxa (than other enterotypes) / less overall diversity (of taxa);
Samples of feces were collected from 40 individuals and were immediately frozen to preserve them. The numbers of bacteria in the feces (cell counts / 1011 cells g-1) were later measured and the enterotype was determined. The box plot shows this data. Each data point shows the cell count from one fecal sample.
[Source: Material from: Vandeputte, D., Kathagen, G., D’hoe, K. et al., Quantitative microbiome profiling links
gut community variation to microbial load, published 2017, Nature, reproduced with permission of SNCSC.]
Estimate the median number of bacterial cells per gram of feces in the R enterotype.
[1]
1.9 × 1011 / 190000 million / 190 billion (cells per gram);
Cells per gram not needed as in stem. Accept 1.80 × 1011 to 1.95 × 1011.
Distinguish between the cell counts in the R and B2 enterotypes.
[2]
- lower values for cell counts in B2 (than in R) / converse
OR
median is higher in R (than in B2) / R median is 1.9 versus B2 median is 1.1
OR
lower number of cell counts in R; - all counts in R higher than third/75th/upper quartile in B2
OR
25-75 % range (box) in B2 is smaller than in R; - R maximum 3.1 versus B2 maximum is 2.1
OR
R maximum is higher than B2 max; - B2 minimum is lower than R minimum;
The ranges are basically the same.
Comment on the data for the P enterotype.
[1]
- only one sample/count/data point;
- only analysed feces from one person (with this enterotype);
- not a big enough sample;
Statins are drugs that are commonly prescribed to reduce cholesterol concentrations in the blood. As part of research into the effects of statins, the enterotype and body mass index (BMI) of 782 individuals were determined. The results are shown in the stacked graph.
[Source: Material from: Vieira-Silva, S., Falony, G., Belda, E. et al., Statin therapy is associated with lower
prevalence of gut microbiota dysbiosis, published 2020, Nature, reproduced with permission of SNCSC.]
Estimate the prevalence of the P enterotype at a BMI of 50.
[1]
0.35;
Accept any values between 0.33 and 0.37.
Accept 35%.
State the relationship between BMI and the prevalence of the B2 enterotype.
[1]
B2 is associated/commoner/more prevalent in people with higher BMI
OR
(prevalence of) B2 increases as BMI increases;
Accept positive correlation/OWTTE.
Evaluate the evidence provided by the data in the graph for the hypothesis that the R enterotype causes low BMI.
[2]
- R is more common/prevalent in people with low BMI;
- statement about it being far more common;
- but this correlation does not prove that R causes low BMI;
- low BMI could(actually) be the cause of higher prevalence of R;
So ‘R is far more common in people with low BMI’, would gain both a and b.
The 782 individuals for whom BMI and enterotype had been determined were divided into four groups, according to whether or not they were taking statins and their BMI category. The prevalence of the four enterotypes in each of these groups is shown as a percentage in the pie charts.
[Source: Material from: Vieira-Silva, S., Falony, G., Belda, E. et al., Statin therapy is associated with lower
prevalence of gut microbiota dysbiosis, published 2020, Nature, reproduced with permission of SNCSC.]
The prevalence of inflammatory bowel disease rises with increases in BMI. At any BMI level, individuals with the B2 enterotype have a higher prevalence of inflammatory bowel disease than with other enterotypes. Using the data in the graph, discuss whether statins could reduce the incidence of inflammatory bowel disease.
[2]
- high/highest % of B2 enterotype in people with BMI greater than (or equal to) 30 with no statins
OR
taking statins could reduce the percentage of B2 enterotype in people with BMI ≥ 30
OR
reducing BMI to below 30 could lower % of people with B2 enterotype without taking statins; - but statins may not cause a person to change from B2 to another enterotype
OR
lower B2 in those taking statins if BMI is > 30 so might reduce IBD/inflammatory bowel disease
OR
but when BMI < 30, there is almost double the prevalence of B2 in those taking statins so might not have an effect / increase (prevalence of) inflammatory bowel disease;
One for correct data and one for discussion