AQA AS Level Biology Paper 1, November 2020: Question 8
9 marks · Medium difficulty · Practical Techniques & Data Analysis
Draw a histogram to represent birth mass frequency density data, calculate the number of babies with low birth mass using a provided table and equation, and state three conclusions from a line graph showing infant survival against birth mass for smokers and non-smokers.
Practise this questionQuestion
Question text
08 A scientist investigated birth mass in a population of babies. She determined the
birth mass (b) of babies and grouped this information into different ranges of
birth mass.
Her results are shown in Table 4.
Table 4
Birth mass b / kg Range of Frequency
mass / kg density
0.0 < b ⩽ 2.0 2.0 5 000
2.0 < b ⩽ 2.5 0.5 20 000
2.5 < b ⩽ 3.0 0.5 90 000
3.0 < b ⩽ 3.5 0.5 260 000
3.5 < b ⩽ 4.5 1.0 200 000
4.5 < b ⩽ 5.5 1.0 20 000
Frequency density is calculated using this equation
number of babies
Frequency density19 =
range of mass
08.1 Draw, on Figure 8, a suitable chart to show the distribution of birth mass for this
population of babies.
[4 marks]
Figure 8
08.2 Babies with birth mass less than 2.5 kg are classified as low birth mass.
Use information in Table 4 and the equation to calculate the number of babies born
with low birth mass in this population.
Show your working. 20
[2 marks]
The scientist also measured the relationship between birth mass and babies surviving
less than 4 weeks. She determined if the mothers of these babies smoked cigarettes
during pregnancy. Her results are shown in Figure 9.
Figure 9
Answer
08.3 State three conclusions that can be drawn from the data in Figure 9.
[3 marks]
Mark scheme
Show the mark scheme
Question Marking Guidance Mark Comments
08.1 Histogram 4 Reject answers where
1. Linear scale for y axis; data for frequency
density and birth
2. Linear scale for x axis; mass not used
3. Correct bar widths and touching;
4. All bar heights plotted accurately;
OR
Bar chart accept for 3 marks,
5. Linear scale for y axis;
6. Labelled bars of equal width and not touching;
7. All bar heights plotted accurately;
OR
Graph accept for 2 marks,
8. Linear scale for y axis;
9. All co-ordinates plotted accurately for frequency
density;
08.2 Correct answer for 2 marks = 20 000;; 2
Accept for 1 mark, rearranged equation (eg number
of babies = frequency density × range of mass)
08.3 1. Survival increases as the birth mass increases; 3
2. Survival decreases with smoking;
3. Effect of smoking (on number) similar at all birth
masses;
TOTAL 9
How to answer it
Investigation into Birth Mass and Infant Survival
What this question tests
This question assesses your ability to process biological data involving unequal class widths, calculate underlying frequencies using frequency density formulas, construct appropriate graphical representations (histograms), and interpret complex biological curves relating maternal habits (smoking) to infant survival rates.
Constructing a Suitable Chart
✅ Correct Answer Requirements (Histogram)
- Linear scale plotted on the y-axis (Frequency density).
- Linear scale plotted on the x-axis (Birth mass / kg).
- Bars must be drawn with correct widths corresponding to class intervals and must touch each other.
- All bar heights plotted accurately based on Table 4 values.
🧠 Exam Technique
Because the class intervals (range of mass) in Table 4 are unequal (e.g., 2.0 vs 0.5), plotting a standard bar chart would distort the data representation. Examiners explicitly look for a histogram where area represents frequency, meaning bar heights must reflect frequency density.
❌ Common Errors
- Leaving gaps between bars (treating it like a bar chart or bar graph).
- Plotting raw frequency numbers directly onto the y-axis instead of calculating or using the given frequency density values.
- Using non-linear scales on either axis.
Calculating Low Birth Mass Frequency
📐 Step-by-Step Calculation
- Identify relevant data: Low birth mass is defined as less than 2.5 kg . From Table 4, this covers two groups: 0.0 < b ≤ 2.0 and 2.0 < b ≤ 2.5 .
- Rearrange the equation:
number of babies = frequency density × range of mass - Calculate for group 1 (0.0 to 2.0 kg):
5 000 × 2.0 = 10 000 - Calculate for group 2 (2.0 to 2.5 kg):
20 000 × 0.5 = 10 000 - Sum both values:
10 000 + 10 000 = 20 000
💡 Key Knowledge
The formula provided in the stem ( Frequency density = number of babies / range of mass ) is a core mathematical biology tool. Rearranging equations correctly is heavily rewarded when interpreting grouped frequency data.
❌ Common Calculation Traps
- Forgetting to add the two separate low-mass groups together, resulting in an incomplete final value of 10 000.
- Incorrectly reading the range of mass values from Table 4.
Interpreting Graphical Trends (Figure 9)
✅ Acceptable Conclusions
- Trend 1: Survival increases as birth mass increases (curve slopes downwards for babies surviving less than 4 weeks per 1000 live births).
- Trend 2: Survival decreases with smoking (the dashed line representing mothers who smoked sits higher across most intervals, meaning more deaths/fewer survivors).
- Trend 3: The effect of smoking is relatively similar across all birth masses (the distance/gap between the two curves remains fairly constant).
🧠 Exam Technique
When answering "state conclusions from data" questions, always check the axis labels carefully. Note that the y-axis shows babies surviving less than 4 weeks (i.e., early mortality), so a downward trend on the graph actually equates to better survival rates as mass increases.
❌ Common Errors
Confusing mortality indicators with survival rates—stating that "survival decreases as birth mass increases" misreads the negative gradient of the curves. Always trace axes carefully before writing down comparative statements.
Topics
Practical skills · Biology · Data analysis · 3.4 Genetic information, variation and relationships between organisms
Question and mark scheme from the AQA AS Level Biology examination, Paper 1, November 2020. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.