AQA GCSE Biology Biology Paper 2 (Higher), June 2024: Question 7
13 marks · High Demand difficulty · Extended Answer
Calculate the land area needed to feed chickens, construct a pyramid of biomass, calculate a biomass ratio, and analyze amino acid data in maize.
Practise this questionQuestion
Question text
07 Farmers can increase the growth rate of farm animals by controlling the
animals’ diets.
A farmer has 1000 chickens.
• The farmer feeds the chickens on seeds from maize plants.
• 1 hectare of land produces 16.4 tonnes of maize seeds.
• The maize seeds have an energy content of 16 MJ per kg.
• Chickens can use 80% of the energy in maize seeds.
• Each chicken needs 46 MJ of energy to grow to full size.
07.1 Calculate the area of land needed to provide enough energy from maize seeds for
1000 chickens to grow to full size.
Give your answer in m2.
Give your answer to 3 significant figures.
1 hectare = 10 000 m2
1 tonne = 1000 kg
[5 marks]
Area of land (3 significant figures) =28 m2
07.2 Another farmer produced 4200 kg of maize seeds in a field.
The farmer fed the maize to 1000 chickens.
At full size, the mean mass of one chicken was 2.2 kg.
Complete Figure 11 to show a pyramid of biomass for the food chain from the maize
seeds to 1000 chickens.
[3 marks]
You should:
• label the x-axis
• use a suitable scale.
Figure 11
07.3 Calculate the ratio of chicken biomass to maize seed biomass.
Use data from Question 07.2.
Give your answer in its simplest form.
[2 marks]
Ratio = :
07.4 Chickens can use 80% of the biomass from the maize seeds they eat for respiration
and growth.
What happens to the remaining 20% of the biomass in the maize seeds?
*28* [1 mark]
Protein is an important part of a chicken’s diet.
• Proteins contain 20 different types of amino acid.
• A chicken can make many of the 20 amino acids from other substances in the diet.
• Essential amino acids are amino acids the chicken cannot make.
• Essential amino acids must be included in the diet.
Maize seeds contain protein but the proportion of some essential amino acids is low.
Scientists have produced a type of maize called Quality Protein Maize (QPM).
Table 2 compares the proportions of seven essential amino acids in normal maize
seeds and in QPM seeds.
Table 2
Mass of amino acid in protein in g/kg
Amino acid
Normal maize Quality protein maize (QPM)
Leucine 122.2 88.1
Lysine 28.9 41.9
*29*Methionine 19.9 18.1
Phenylalanine 49.4 40.9
Threonine 34.5 36.5
Tryptophan 7.3 16.3
Valine 3145.9 51.2
07.5 Which amino acids are found in significantly higher proportions in the QPM seeds?
[1 mark]
Tick ( ) one box.
Lysine and tryptophan
Lysine and valine
Threonine and tryptophan
Threonine and valine
07.6 Table 2 shows that 1 kg of QPM contains less leucine than 1 kg of normal maize.
Suggest why a diet containing less leucine does not slow down the growth
of chickens.
[1 mark]
Mark scheme
Show the mark scheme
Question 7
AO /
Question Answers Extra information Mark
Spec Ref.
07.1 46000 or 16400 or 12.8 1 AO2
or 0.8 4.7.2.1
4.7.4.3
4.7.5.2
46000 and 16400 1
or
262400
46000 and 209920 1
or
3593.75
2191.3 1
or
46 000 10 000
209 920
or
3593.75 10 000
16 400
2190 – – 1 –
AO /
Spec Ref.
07.2 suitable scale, symmetrical 1 AO2
around 0 4.7.4.2
labels for x-axis (biomass in) kg 1
and for bars (bars) maize and chickens
correct values plotted: allow a tolerance of ½ small 1
chickens 2200 square
maize 4200 ignore height of bars
AO /
Spec Ref.
07.3 2200 1 AO2
4200 4.7.4.2
= 0.5238… : 1 allow rounded value 1
or
11 : 21
or
1 : 1.9
AO /
Spec Ref.
07.4 lost via egestion / faeces ignore urine / excretion / waste 1 AO1
ignore not digested 4.7.4.3
do not accept respiration
do not accept not eaten
do not accept movement or as
heat or for keeping warm
AO /
Spec Ref.
07.5 lysine and tryptophan 1 AO3
– – – 4.4.2.3
4.7.5.2
AO /
Spec Ref.
07.6 any one from: 1 AO3
4.4.2.3
• chickens need low amounts of do not accept leucine is not 4.7.5.2
leucine (for growth) needed (for growth)
• (chicken) proteins contain low
amount / proportion of leucine
Total Question 7 13
How to answer it
Energy Transfer, Biomass Pyramids & Diet in Farming
What this question tests
- Multi-step quantitative skills: Unit conversions (hectares to m², tonnes to kg), percentage efficiency calculations, and working to a specified number of significant figures.
- Ecological representations: Constructing symmetrical, accurately scaled pyramids of biomass from mass data.
- Mathematical relationships: Expressing biomass ratios in simplest forms ( x : 1 or integer ratios).
- Biological energy losses: Distinguishing between metabolic losses (respiration) and unabsorbed losses (egestion/faeces).
- Data analysis & nutrition: Interpreting comparative dietary tables and explaining biological requirements of essential amino acids.
Land Area Required for Maize Production
Calculate the area of land (in m²) needed to feed 1000 chickens to full size (3 significant figures).
📐 Step-by-Step Calculation
1000 chickens × 46 MJ = 46 000 MJ
16 MJ/kg × 0.80 = 12.8 MJ per kg
46 000 MJ ÷ 12.8 MJ/kg = 3593.75 kg
1 hectare = 16.4 tonnes = 16 400 kg
1 hectare = 10 000 m²
Yield per m² = 16 400 kg ÷ 10 000 m² = 1.64 kg/m²
(Alternative: Energy yield per m² = [16 400 kg × 12.8 MJ/kg] ÷ 10 000 = 20.992 MJ/m²)
Area = 3593.75 kg ÷ 1.64 kg/m² = 2191.31... m²
(Or: 46 000 MJ ÷ 20.992 MJ/m² = 2191.31... m²)
2191.31... rounds to 2190 m²
✅ Mark Scheme Breakdown
- Mark 1: Finding total energy needed (46 000) OR kg per hectare (16 400) OR usable energy/kg (12.8).
- Mark 2: 46 000 AND 16 400, OR total gross energy per ha (262 400 MJ).
- Mark 3: Total usable energy per ha (209 920 MJ) OR total kg needed (3593.75 kg).
- Mark 4: Correct unrounded area: 2191.3 m².
- Mark 5: Final answer rounded to 3 s.f.: 2190 m².
❌ Common Calculation Traps
- Forgetting 80% efficiency: Using 16 MJ directly gives an area of 1753 m² (loses 2 marks).
- Unit conversion errors: Mixing tonnes and kg (e.g. using 16.4 instead of 16 400).
- Ignoring significant figures: Leaving the answer as 2191 or 2191.3 automatically loses the 5th mark.
Constructing a Pyramid of Biomass
Complete Figure 11 for the food chain: Maize seeds → 1000 Chickens.
🧠 How to Draw the Pyramid (Examiner Guide)
Values to plot:
- Producers (Maize seeds): Total mass = 4200 kg (bottom bar).
- Primary consumers (Chickens): 1000 chickens × 2.2 kg = 2200 kg (top bar).
Constructing the graph:
- Symmetry: The pyramid MUST be symmetrical around the central zero line ( 0 ).
- Scale: Choose an easy scale, e.g. 1 large grid square = 500 kg or 1000 kg.
- Bottom bar (Maize = 4200 kg): Plot 2100 kg to the left and 2100 kg to the right of zero.
- Top bar (Chickens = 2200 kg): Plot 1100 kg to the left and 1100 kg to the right of zero.
- Labels: Label the x-axis with "Biomass in kg" and label each bar clearly ("Maize seeds" at base, "Chickens" above).
✅ Marking Criteria
- Mark 1: Suitable linear scale chosen AND bars plotted symmetrically around 0.
- Mark 2: Label on x-axis (biomass in kg) AND labels for both bars (maize and chickens).
- Mark 3: Correct widths plotted (tolerance ±0.5 small square). Note: height of bars is ignored.
❌ Common Errors
- Plotting the chicken bar for 2.2 kg instead of total biomass (2200 kg).
- Starting the bars from the left-hand edge instead of centring them on 0.
- Forgetting to include units ("kg") on the x-axis label.
Biomass Ratio
Calculate the ratio of chicken biomass to maize seed biomass in its simplest form.
📐 Step-by-Step Simplification
Order is crucial: Chicken biomass : Maize biomass
2200 : 4200
2200 ÷ 200 = 11
4200 ÷ 200 = 21
Simplest whole-number ratio = 11 : 21
Divide both sides by 4200 → 0.52 : 1
Divide both sides by 2200 → 1 : 1.9
✅ Mark Allocation
- 1st Mark: Showing working fraction: 2200 / 4200 .
- 2nd Mark: Correct final simplified form:
11 : 21 OR 0.52 : 1 OR 1 : 1.9.
Fate of Biomass
Chickens use 80% of biomass for respiration and growth. What happens to the remaining 20%?
✅ Correct Answer
Lost via egestion / as faeces (unabsorbed food).
❌ What NOT to say (Crucial Distinctions)
- Do NOT say "respiration" or "heat": The stem explicitly said respiration is already accounted for in the 80%!
- Do NOT say "excretion" or "urine": Excreted products (like urea/uric acid) come from digested, metabolised substances, not the unabsorbed 20% bulk.
- Do NOT say "not eaten": The question specifies "biomass from seeds they eat".
Quality Protein Maize (QPM) & Amino Acids
07.5: Which amino acids are found in significantly higher proportions in QPM seeds? [1 mark]
✅ Correct Option: Lysine and tryptophan
Looking at Table 2:
- Lysine: increases from 28.9 g/kg to 41.9 g/kg (+45% increase).
- Tryptophan: increases from 7.3 g/kg to 16.3 g/kg (+123% increase, more than doubled).
- Other options (valine, threonine) show only tiny increases or decreases.
07.6: Why does a diet containing less leucine NOT slow down chicken growth? [1 mark]
✅ Acceptable Answers (Any one)
- Chickens only need a low amount of leucine (for growth).
- Chicken proteins contain a low proportion / amount of leucine.
❌ Rejected Answer
"Chickens do not need leucine" — Leucine was stated in the question as an essential amino acid, meaning chickens cannot make it and DO need it, just in small quantities.
Topics
Biology · B7: Ecology
Question and mark scheme from the AQA GCSE Biology examination, Biology Paper 2 (Higher), June 2024. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.