AQA GCSE Combined Science: Trilogy Biology Paper 2 (Higher), November 2021: Question 3

✅ Correct Answer

Ourasphaira

💡 Key Knowledge

Organisms are named using the binomial system (Linnaeus):

• First word: Genus (always capitalised, e.g. Ourasphaira).
• Second word: Species (lowercase, e.g. giraldae).

❌ Common Errors

Writing the full binomial name ( Ourasphaira giraldae ) or writing the species name ( giraldae ). The mark scheme strictly rejects the combined two-word name.

✅ Correct Answer

Tick box 2:

"The mud stopped oxygen reaching the fungus."

💡 Key Knowledge

Decay requires oxygen, warmth, and moisture for aerobic microorganisms (bacteria and fungi) to break down organic matter.

Mud creates an anaerobic (oxygen-free) environment, preventing decay microbes from surviving and allowing parts of the organism to be preserved as fossils.

❌ Common Errors

Ticking "The fungus completely decayed in the mud" — complete decay leaves no organic remains or shape behind to form this type of fossil.

📐 Step-by-Step Calculation

Find the difference between maximum and minimum values:

1. Identify values:
   Upper limit = 1.1 × 10⁹ years
   Lower limit = 8.9 × 10⁸ years
2. Convert to matching powers of 10 (or ordinary numbers):
   1.1 × 10⁹ = 11 × 10⁸ (or 1,100,000,000)
   8.9 × 10⁸ = 8.9 × 10⁸ (or 890,000,000)
3. Subtract:
   (11 × 10⁸) − (8.9 × 10⁸) = 2.1 × 10⁸
   Or: 1,100,000,000 − 890,000,000 = 210,000,000

✅ Acceptable Answers

• 2.1 × 10⁸
• 210 000 000

❌ Common Errors

Forgetting that the powers are different (10⁹ vs 10⁸) and simply calculating 8.9 − 1.1 = 7.8 × 10⁸. Always match exponents before subtracting!

✅ Any ONE valid reason

• Fossils of the fungus may have been destroyed by geological activity (e.g. tectonic plate movement, earthquakes, erosion).
• Fossils may not have been found yet.
• Dating methods (e.g. radiometric dating of surrounding rock) are not completely precise / accurate.
• The exact time an organism evolves / speciates from ancestors is difficult to pinpoint.

🧠 Exam Technique

The prompt specifically states "Humans did not exist...", so responses saying "no written records" or "nobody was there to record it" will receive 0 marks.

❌ Common Errors

Vague answers like "some were destroyed" or "some not found" without specifying fossils/evidence are ignored by examiners. Always mention geological activity for why early fossils are missing.

✅ Correct Answer

Eukaryota (or eukaryote / eukaryotes)

💡 The Three Domains

• Archaea: Primitive prokaryotes, often extremophiles.
• Bacteria: True bacteria (prokaryotes).
• Eukaryota: Organisms with complex cells containing a nucleus and membrane-bound organelles (Protists, Fungi, Plants, Animals).

❌ Common Errors

Confusing domains with kingdoms (e.g. writing "Fungi" as the domain). The only valid domain choices are Archaea, Bacteria, or Eukaryota.

✅ Correct Checkboxes (Select TWO)

• ☑ Can survive in extreme environments [1]
• ☑ Cytoplasm contains DNA [1]

💡 Key Knowledge

• Extremophiles: Many Archaea are adapted to survive in harsh conditions (high temperatures, high salt concentrations, deep sea vents).
• Prokaryotic nature: Archaea are prokaryotes. They do not have a nucleus, so their genetic material (DNA) is free in the cytoplasm.
• They do not contain chloroplasts (only plant/algal cells have these).

❌ Common Errors

Selecting "Cells do not have a cell wall" (most Archaea do have cell walls) or "Cells contain chloroplasts" (only photosynthetic eukaryotes have chloroplasts).

✅ Any THREE from:

• Studies of internal / cell structures with light microscopes [1]
• Studies of internal / cell structures with electron microscopes [1]
• DNA / genetic analysis (e.g. base sequence comparison) [1]
• Chemical analysis [1]
• Comparison of biochemical processes (e.g. protein synthesis, enzymes) [1]
• Studies of evolutionary relationships [1]

🧠 Exam Technique

Notice how the mark scheme treats microscopes:

• Mentioning both light and electron microscopes earns 2 marks!
• Just saying "using microscopes" generally earns only 1 mark.
• Pair DNA / genetic analysis with electron microscopy and biochemical analysis for an easy 3/3.

❌ Common Errors

Describing physical traits (e.g. "whether it has legs or wings", "colour", "shape"). The question clearly states: "Do not refer to appearance". Answers based on observable anatomy score zero.