AQA GCSE Biology Biology Paper 1 (Foundation), June 2023: Question 3

✅ Correct Answer

carbon dioxide + water → glucose + oxygen

• Left side: carbon dioxide [1 mark]
• Left side: water [1 mark] (either order on LHS)
• Right side: glucose [1 mark]

❌ Common Errors

• Writing chemical formulas instead of words when words are provided in the box (e.g., writing CO₂ instead of selecting from the given words).
• Confusing photosynthesis with respiration and putting glucose on the left.
• Guessing unrelated nutrients like protein or fat.

✅ Mark Scheme Breakdown

• Mark 1: Used in (aerobic) respiration.
• Mark 2: To release energy (or transfer energy / for energy).

❌ Examiner Traps to Avoid

• "Energy is made / created / produced": Never say energy is created! The law of conservation of energy applies. Say energy is released or transferred.
• Do not write anaerobic respiration — oxygen is required specifically for aerobic respiration in the mitochondria.

✅ Acceptable Hazard & Risk Pairs (Choose ONE)

• Hazard: Lamp / bulb gets hot
  Risk: May burn skin / cause a burn.
• Hazard: Glassware / beaker is breakable
  Risk: May cut skin.
• Hazard: Water near electricity / electrical wires
  Risk: Electric shock.
• Hazard: Scalpel / scissors (to cut pondweed)
  Risk: May cut skin.

🧠 Exam Technique: Hazard vs Risk

Make sure you understand the difference:

• Hazard: The object or situation with potential to cause harm (e.g. hot bulb).
• Risk: The injury or damage that could result (e.g. burning fingers).

These marks are awarded in pairs; the risk must match your stated hazard.

✅ 03.4 How to Keep Temperature Constant

Give any one practical method [1 mark]:

• Place the beaker in a water bath.
• Put the beaker inside a larger beaker of water (heat buffer).
• Use a heat shield / clear plastic/glass screen between the lamp and beaker.
• Use an LED bulb (which emits very little heat).

✅ 03.5 Why Temperature Must Be Controlled

• Mark 1: Temperature affects the rate of photosynthesis / temperature is a limiting factor / temperature affects enzyme activity.
• Mark 2: Therefore it would change the number of bubbles / affect the results / invalidate the experiment.

✅ 03.6 Highest Photosynthesis Rate

Answer: Blue [1 mark]

From Table 3, blue light produced 46 bubbles in 2 minutes, which is higher than red (38), yellow (29), or green (8).

✅ 03.7 Best Way to Display Data

Answer: Bar graph [1 mark]

• The independent variable (colour of light) is categoric / discrete data (distinct categories, not continuous numbers).
• Line graphs and scatter graphs require continuous numerical data on both axes.

✅ Correct Equipment (Any ONE)

• (Gas) syringe [1 mark]
• Measuring cylinder (inverted over water) [1 mark]
• Burette [1 mark]

🧠 Exam Technique: Volume vs Rate

Counting bubbles only tells you the number of bubbles, not their size or volume. To quantify volume precisely, apparatus with calibrated graduation marks is essential. A beaker or boiling tube alone cannot measure volume accurately.

✅ Mark Scheme Requirements

• Mark 1: As light intensity increases, the rate of photosynthesis increases (positive correlation).
• Mark 2: The increase is at a constant rate / linear / a straight line through the origin.
• Shortcut: Stating that rate is "directly proportional" to light intensity secures both marks immediately!

🧠 What Top Students Do

A complete description of a graph has two parts:

1. The overall trend (increases as X increases).
2. The pattern or proportionality (linear, directly proportional, or levels off). Notice on Figure 1 that the line goes straight from (0,0) to (5,16) without leveling off!