▶️ Answer/Explanation
(a)
From the stacked column graph:
- High abundance of Bacteroides: B2 has the highest relative abundance of Bacteroides (around 45%).
- Low abundance of Ruminococcus: B2 shows the lowest level of Ruminococcus compared to other enterotypes.
- Low abundance of Faecalibacterium: Noticeably less than in enterotype R.
- Very low Prevotella: Almost negligible, unlike in the P enterotype.
- Lower diversity overall: A smaller portion of “Other Taxa” compared to others.
(b)
From the box plot:
The median for R is approximately 1.9 × 10¹¹ cells/g.
(c) Difference in cell counts between R and B2:
- R enterotype has a higher median (1.9 × 10¹¹) compared to B2 (about 1.1 × 10¹¹).
- Wider range in R, indicating more variability.
- B2’s maximum is still lower than R’s median, showing consistently lower counts in B2.
- B2 has a narrower interquartile range (IQR) and lower overall values.
(d)
- Only one data point shown.
- Sample size too small to draw reliable conclusions.
- Not statistically meaningful.
(e)
(i) Estimate the prevalence of the P enterotype at BMI = 50 (using the pie chart for BMI ≥ 30):
Approximately 13.5%.
(ii) Relationship between BMI and B2 prevalence:
Positive correlation: Prevalence of B2 increases with higher BMI.
(f)
- R is more prevalent in individuals with BMI < 30.
- This is correlation, not causation.
- Could be that low BMI influences microbiota, not the reverse.
- Other factors (e.g. diet, genetics) might influence both BMI and microbiota composition.
(g)
- B2 enterotype is associated with higher IBD prevalence.
- Among individuals with BMI ≥ 30:
- Without statins: B2 prevalence = 17.7%.
- With statins: B2 prevalence = 5.9%.
- Statins appear to reduce B2 prevalence, possibly reducing IBD risk.
- But in BMI < 30:
- With statins, B2 increases slightly (7.3% vs. 3.9%).
- Suggests context-dependent effect of statins.
- Conclusion: There is some evidence that statins may reduce B2 prevalence—and hence IBD risk—in high-BMI individuals, but not conclusively for everyone.
Markscheme:
(a)
- 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.
(b) 1.9 × 1011 / 190,000 million / 190 billion cells per gram.
(c)
- Lower values for cell counts in B2 than in R / median is higher in R (1.9 vs. 1.1).
- All counts in R higher than third quartile in B2 / 25–75% range in B2 is smaller than in R.
- R maximum 3.1 versus B2 maximum 2.1 / B2 minimum is lower than R minimum.
(d)
- Only one sample/data point / analyzed feces from one person.
- Not a big enough sample.
(e)
- (i) 0.35.
- (ii) B2 is more prevalent in people with higher BMI / prevalence of B2 increases as BMI increases.
(f)
- R is more common in people with low BMI.
- Correlation does not prove causation (R may not cause low BMI).
- Low BMI could cause higher prevalence of R.
(g)
- Highest % of B2 in BMI ≥ 30 without statins; statins may reduce B2 in this group, potentially lowering IBD.
- But statins may not change enterotype directly / when BMI < 30, statins nearly double B2 prevalence (could increase IBD).
- Confounding factors: BMI reduction itself lowers B2 prevalence without statins.
▶️ Answer/Explanation
(a)
- Japan: 6000 steps/day
- USA: 4000 steps/day
(b)
- The UK has a higher mode (4000 steps/day) compared to Saudi Arabia (3000 steps/day).
- The UK’s data is more spread out, indicating greater variation in activity levels.
- People in the UK take more steps on average than those in Saudi Arabia.
(c)
- Highest walkability: New York
- Lowest walkability: Charlotte
(d)
- Cities with high walkability encourage more people to walk, reducing variation in steps.
- In low walkability cities, fewer people walk regularly, and some may not be active at all.
- People walk more when they don’t need to drive everywhere (e.g., shops, parks, jobs nearby).
(e)
Similarities:
- Obesity decreases as steps per day increase for both males and females.
- For both, the rate of obesity levels off after about 8000 steps/day.
Differences:
- Females show a bigger decrease in obesity rates with more steps than males.
- At 1000 steps/day, female obesity is higher than male obesity.
- Overall, females benefit more from increased walking in reducing obesity.
(f)
- Obese individuals may take fewer steps due to limited mobility or lifestyle.
- Being less active (fewer steps) may lead to obesity over time.
(g)
- There is a positive correlation: as activity inequality increases, obesity rates increase.
(h)
- Improve city design to make walking easier—e.g., more sidewalks, parks, shorter distances.
- Educate the public on the benefits of daily walking and being active.
Markscheme:
(a)
Japan: 6000 and USA: 4000 (both needed)
(b)
a. Higher mode for the number of steps in UK (4000 versus 3000 in Saudi Arabia)
b. UK has more variation/is more spread out/greater standard deviation OR UK has a more normal distribution
c. People in UK take more steps than people in Saudi Arabia
(c)
Highest: New York and lowest: Charlotte (both needed)
(d)
a. Majority of individuals are active/walk to places if walkability is high OR high walkability encourages the habit of walking so the coefficient of activity inequality would be low
b. With low walkability some individuals take exercise/go jogging and some do not
c. (With high walkability) people don’t need to drive increasing the incentive to walk
(e)
Similarities (Compare):
a. Lower percentage of obesity with more steps per day in both males and females OR percentage obesity is most similar at 1000 steps OR correlation of steps to percent obesity plateaus after 8000 steps for both males and females
Differences (Contrast):
b. The range difference of obesity percentage among different steps is bigger in females (9% – 31% versus 18% to 30%) OR walking has a greater impact on lowering obesity rates in females than males OR men show a greater percentage of obesity OR at 1000 steps per day there are more obese women than men
(f)
(any order)
a. Obesity causes people to be less active/take fewer steps
b. People who are less active/take fewer steps (are more likely to) become obese
c. People who are not obese tend to have healthier habits, including walking more
(g)
As activity inequality rises percentage obesity rises OR Positive/direct correlation/relationship
(h)
a. Use public education to encourage people to walk more/become more active
b. Improve city design to improve walkability
c. Reduce distances between homes/shops/workplaces/parks
d. More sidewalks/make it easier for pedestrians to cross roads/other specific measure
▶️ Answer/Explanation
(a)
Cellular respiration – a process where organisms break down glucose to release energy, producing carbon dioxide as a waste product, which is then released into the water.
(b)
Photosynthesis by phytoplankton or algae – these autotrophic organisms fix carbon dioxide from the water or atmosphere and convert it into organic compounds, which enter the marine food chain
(c)
Energy enters the marine ecosystem when sunlight is captured by photosynthetic organisms like phytoplankton.
• Energy flows through the food chain as organisms consume one another, moving from producers to primary consumers, and then to higher trophic levels.
• At each level, energy is lost due to:
– Respiration, which releases heat
– Excretion and waste products
– Undigested material (not all parts of prey are consumed or absorbed)
• This loss of energy at each step limits the number of trophic levels in marine food chains.
(d) (i)
Crustacea are a richer source of carbon – the black area (carbon content) in the diagram is larger in proportion to their wet mass than in jellyfish, meaning they provide more usable carbon for consumers.
(ii)
Disadvantage – Jellyfish have a large wet mass but low carbon content, which means they provide low nutritional value to predators.
• This makes them less efficient as a food source despite their size, and more energy is needed to maintain their large, water-filled bodies.
Markscheme:
(a) Carbon dioxide loss:
- (aerobic/cellular) respiration
- gas exchange/diffusion (Do not accept photosynthesis or breathing)
(b) Alternative carbon sources:
- photosynthesis
- absorption of (dissolved) carbon dioxide/(hydrogen)carbonate directly from oceans
(c) Energy flow in marine food chains:
- Light energy → chemical energy (photosynthesis)
- Energy flows through food chains/webs via feeding
- Only ~10% energy transferred between trophic levels
- Energy lost as heat (respiration)
- Energy not recycled
- Undigested detritus/fossils trap remaining energy
(d)(i) Carbon source comparison:
- Crustaceans (more carbon per unit volume)
(d)(ii) Jellyfish body mass:
- Advantages:
- Can eat larger prey
- Lower predation rates
- More reproductive cells
- Disadvantages:
- Slower movement
- Higher energy demands
- Lower SA:Vol ratio (exchange limitations)
- More prone to storm damage
▶️ Answer/Explanation
(a)
- The study diet has an average energy content slightly lower than the habitual diet.
However, the standard deviations overlap, indicating no significant difference in total energy between the two diets.
(b)
- The study diet has a higher percentage of saturated fats (about 60%) compared to the habitual diet (about 37%).
- The study diet has a lower percentage of unsaturated fats (both monounsaturated and polyunsaturated) compared to the habitual diet.
Additionally, the study diet contains slightly less carbohydrate than the habitual diet.
(c)
- Initial mean cholesterol level = 150 mg/dL
- Mean cholesterol after 1 week = 165 mg/dL
Answer: 10% increase in mean cholesterol level after one week.
(d) (i)
- Both before and after the diet, plasma insulin levels increase rapidly within 30 to 45 minutes after glucose intake.
- Insulin levels then plateau and gradually decrease over time.
The patterns and values are very similar, with overlapping error bars, indicating no significant difference between before and after the study diet.
(d) (ii)
- β (beta) cells of the islets of Langerhans in the pancreas secrete insulin.
(d) (iii)
- After glucose is consumed, blood glucose levels rise, triggering β cells to secrete insulin.
- Insulin helps cells take up glucose from the blood, which lowers blood glucose levels.
(e)
Supported:
- The study diet, which had higher saturated fat content, caused an increase in cholesterol levels.
- This supports the idea that saturated fats raise the risk of coronary artery disease.
Not Supported:
- There was no significant change in insulin response, so the study does not support a link between saturated fat and diabetes risk.
- The study lasted only two weeks, which may be too short to observe long-term effects on diabetes or artery blockage.
Markscheme:
a.
Energy content is similar/not significantly changed between the two diets;
b.
1. Study diet has higher percentage of saturated fats (15% vs 10%);
2. Habitual diet contains more unsaturated fats (polyunsaturated 6% vs 3%);
3. Slightly less carbohydrate in study diet (45% vs 48%);
c.
Calculation: \(\frac{(165-150)}{150} \times 100 = 10\%\)
(Accept range 10-11.3% depending on exact values used)
d.i.
1. Both show similar insulin response patterns over time;
2. Error bars overlap significantly at all time points;
d.ii.
β-cells of pancreatic islets (of Langerhans);
d.iii.
Insulin rises in response to increased blood glucose levels;
e.
Supported:
1. Increased saturated fats led to higher cholesterol levels (risk for coronary artery disease)
Not Supported:
2. No difference in insulin response (no increased diabetes risk shown)
3. Study duration (2 weeks) may be too short to show long-term effects