AQA GCSE Biology Biology Paper 1 (Foundation), June 2022: Question 5

✅ Correct Answer

carbon dioxide + water → glucose + oxygen

(Products can be written in either order. Chemical formulas C₆H₁₂O₆ and O₂ are also credited.)

💡 Key Knowledge

• Reactants: Taken in from the air (carbon dioxide) and soil (water).
• Energy source: Light absorbed by chlorophyll in chloroplasts.
• Main product: Glucose (sugar used for respiration or stored as starch).
• By-product: Oxygen gas released via stomata.

✅ Correct Answer

• Water moves from the roots to the leaves in the xylem.
• Water is lost from leaves through pores called stomata.
• Dissolved sugars are transported in the phloem.

🧠 Exam Technique: Memory Hooks

• Xylem: Carries water and mineral ions upwards in the transpiration stream (dead, hollow tubes).
• Phloem: Carries food (dissolved sugars/sucrose) by translocation (living cells). Sound link: Phloem = Food.
• Stomata: Small openings controlled by guard cells for gas exchange and transpiration.

❌ Common Errors

Mixing up stomata and guard cells. Stomata are the actual pores; guard cells are the cells flanking the pore that control its opening and closing.

📐 Step-by-Step Calculation

1. Identify values from Table 3:
   Species A = 310
   Species B = 254
2. Set up the division (A ÷ B):
   310 ÷ 254 = 1.220472...
3. Round to 2 significant figures:
   First two significant figures: 1 and 2.
   Look at the 3rd figure (2) → round down.
   Final answer = 1.2

❌ Common Calculation Traps

• Inverting the division: Doing 254 ÷ 310 gives 0.82 (the mark scheme gives partial credit, but you lose the full mark). Always do "target ÷ comparison".
• Incorrect rounding: Writing 1.22 (3 s.f.) or 1 (1 s.f.) loses the final mark. Always re-read the required significant figures!

✅ Correct Answer

☑ Each leaf of species A has more stomata.

💡 Key Knowledge

Water vapour diffuses out of the leaf mainly through open stomata. More stomata mean a greater total surface area available for diffusion, leading to higher rates of transpiration.

✅ Correct Answer

☑ Increased temperature

💡 Why Higher Temperature Increases Transpiration

• Water particles have more kinetic energy, meaning they evaporate and diffuse faster out of the stomata.
• Why other options are wrong: Decreased light closes stomata; decreased wind speed allows humid air to accumulate, reducing the concentration gradient; increased humidity decreases the concentration gradient.

✅ Correct Answer

☑ C

🧠 Exam Technique: Interpreting Data

Deserts have very low water availability. A desert plant must conserve water and minimise water loss. Species C has the lowest transpiration rate (87 arbitrary units) in Table 3, making it the best adapted to conserve water.

✅ Correct Answer

Any one from:

• Stops the plant being eaten / grazed (by herbivores).
• Prevents animals from damaging the plant.
• Reduces water loss (allowable as spines have reduced surface area compared to broad leaves).

🧠 Exam Technique

State a clear biological purpose: say "stops animals eating it" rather than just "protects the plant". Be specific about what it is being protected from.

✅ Correct Answer

• Mark 1: It looks like / mimics a hornet (predators mistake it for a hornet).
• Mark 2: Animals avoid it to avoid the risk of being stung / experiencing pain.

💡 Key Knowledge: Mimicry

The hornet moth displays Batesian mimicry: a harmless species evolves warning coloration resembling a harmful species (the hornet). Predators have learned from past experience that hornets sting, so they avoid anything that shares the hornet's yellow-and-black appearance.

❌ Common Errors

Saying "the moth stings the predator". The question clearly stated that hornet moths do not sting. The survival benefit comes entirely from deception!