AQA GCSE Biology Biology Paper 2 (Foundation), June 2023: Question 4

📐 Step-by-Step Calculation

1. Locate the Outdoors column in Table 3.
2. Identify all input rows:
   • Input as food = 5 950 kJ/m²/year
   • Input as fossil fuel = 50 kJ/m²/year
3. Sum both inputs:
   5 950 + 50 = 6 000

✅ Correct Answer

6 000 (kJ/m²/year)

📐 Step-by-Step Calculation

1. Identify the formula:
   Percentage efficiency = (Energy output ÷ Total energy input) × 100
2. Substitute values for Indoors:
   • Energy output (meat and milk) = 40
   • Total energy input = 16 000 (given in the question prompt)
3. Calculate:
   (40 ÷ 16 000) × 100 = 0.0025 × 100 = 0.25%

✅ Correct Answer & Mark Scheme

• Step 1: Correct substitution: (40 ÷ 16 000) × 100 [1 mark]
• Step 2: Final answer: 0.25 (%) [1 mark]

🧠 Exam Technique: Use Given Values

The question conveniently gave you the total energy input ( 16 000 kJ/m²/year ). Always check if the question provides totals before spending time recalculating them yourself.

❌ Common Errors

• Forgetting to multiply by 100 (giving 0.0025).
• Inverting the division: 16 000 ÷ 40 = 400. Remember efficiency can never exceed 100%!

✅ Correct Selections

• ☑ Cows move less indoors. [1 mark]
• ☑ It is warmer indoors. [1 mark]

💡 Key Knowledge: Biomass Conservation

Intensive farming maximises efficiency by reducing energy losses at each trophic level:

• Reduced movement: Less muscle contraction means less aerobic respiration, saving glucose.
• Warmer environment: Less heat energy lost maintaining body temperature (thermoregulation).
• More remaining energy is converted into biomass (growth/meat and milk).

✅ Correct Answer

Any one point:

• Cows are close(r) together.
• Cows are in an enclosed space.

🧠 Exam Technique

Use comparative words where relevant (e.g. "closer together" rather than just "they are together"). Avoid vague answers like "it is dirty" or "germs like warmth" unless supported by clear biological mechanism.

✅ Correct Answer

Any one letter from:

• D
• G
• H

💡 Key Knowledge: Clear Zones (Inhibition Zones)

• Clear area (no bacterial lawn): Bacteria were killed or inhibited → bacteria are susceptible/sensitive to this antibiotic.
• No clear area (lawn grows right up to disc): Bacteria were unaffected and continued to grow → bacteria are resistant to this antibiotic.
• Discs D, G, and H have no clear rings around them.

Sentence Completion: Cause of Resistance

"Antibiotic resistance in a single bacterium is caused by a change in the bacterium's ________."

💡 Explanation: A random mutation alters the bacterial DNA, producing a new gene that provides resistance (e.g. producing an enzyme that breaks down the antibiotic).

Sentence Completion: Spread of Resistance

"This is because bacteria have a high rate of ________."

💡 Explanation: Bacteria divide very quickly by binary fission (often every 20 minutes under ideal conditions), rapidly passing the mutated resistance gene to offspring.

✅ Mark Scheme: Any TWO points

• Many animals will become ill / many animals may die.
• Resistant bacteria / disease can be passed from animal to animal (or other animals infected).
• Animals cannot be cured (by that antibiotic) / the antibiotic will no longer work.
• Animals become less productive / efficient (less meat or milk produced; reduced growth).
• Farmer loses profit / money (due to lost stock, reduced yield, or unmarketable produce).

❌ Examiner Guidance & Exclusions

• Ignore references to crops: This context is strictly dairy/beef farming.
• Avoid generic single words: Writing just "death" or "money" is too vague. State clearly: "cows may die" or "farmer loses money through reduced milk yield".
• Human health: While resistant bacteria can spread to humans, the question specifically asks why it is a problem for farmers.