AQA GCSE Biology Biology Paper 2 (Foundation), June 2025: Question 8

✅ Mark Scheme Answers (Any 2)

• Buried in sediment / mud / sand / silt [1 mark]
• Soft parts decayed or eaten, leaving hard parts / bones [1 mark]
• Bones / remains replaced by minerals (mineralisation) [1 mark]

💡 Key Knowledge

Fossils can form when:

• Parts of organisms do not decay because conditions needed for decay (oxygen, warmth, moisture) are absent.
• Hard parts (bones, shells) are gradually replaced by minerals over millions of years.
• An imprint or cast is left in soft mud or sediment which subsequently turns into rock.

🧠 Exam Technique

Chronological logic gets the marks: describe what happens immediately after death (burial, flesh rotting), followed by what happens over time (mineralisation).

❌ Common Errors

• "Buried in rock": Incorrect. The organism is buried in sediment or mud, which only becomes sedimentary rock later.
• "Turned to stone": Too vague for GCSE. Always use scientific phrasing like replaced by minerals or mineralised.

📐 Step-by-Step Calculation

Step 1: Identify the given values.

Image length = 120 mm ; Scale = 17 times longer

Step 2: Calculate the real length in mm.

120 mm × 17 = 2040 mm [1 mark for method, 1 mark for value]

Step 3: Convert mm to metres (divide by 1000).

2040 ÷ 1000 = 2.04 m [1 mark]

Final Answer: 2.04 metres

❌ Common Traps

• Dividing by 100 instead of 1000: Giving 20.4 m (confusing cm and mm). Remember: 10 mm = 1 cm; 100 cm = 1 m; so 1000 mm = 1 m.
• Forgetting to convert units: Leaving the answer as 2040 metres. An ichthyosaur is not 2 km long! Always check if your answer is biologically reasonable.

🧠 Error-Carried-Forward (ECF)

If you made an arithmetic error in the multiplication (e.g., writing 2080 mm), you can still gain the final mark if you correctly divide your number by 1000 (e.g., 2.08 m).

✅ Correct Table Entries

• First missing box (above Class): Phylum [1 mark]
• Second missing box (above Genus): Family [1 mark]

Note: Must be in this exact order to score.

💡 Key Knowledge: The Linnaean System

Carl Linnaeus classified living things into a ranked hierarchy:

1. Kingdom (Animalia)
2. Phylum (Chordata)
3. Class (Reptilia)
4. Order (Ichthyosauria)
5. Family (Ichthyosauridae)
6. Genus (Ichthyosaurus)
7. Species (intermedius)

🧠 Memory Aid

Use a popular mnemonic to guarantee full marks:

Kids Prefer Candy Over Fresh Green Spinach

or

King Philip Came Over For Good Soup

❌ Distractor Watch

Words like Community and Population belong to ecology levels of organization, not taxonomy! Mammal is an example of a class, not a classification rank.

✅ Acceptable Answers (Any 2)

• Climate change: Global warming OR an ice age
• Catastrophic event: Asteroid collision OR massive volcanic activity
• New predators: Introduction of a new predator that hunts them
• New disease / pathogen: Epidemic to which they have no resistance
• Competition for mates: Inability to successfully reproduce
• Habitat destruction: Loss of breeding or feeding grounds

❌ What NOT to Write

• "Competition for food": The question specifically asked for other causes, since competition for food was already stated in the prompt.
• "Lack of food" alone: Ignored (not specific enough).
• "Weather": Weather refers to day-to-day changes; extinction is caused by long-term climate change.
• "Pollution": Ichthyosaurs lived millions of years ago, long before human industrial pollution existed.

🧠 Exam Technique: Read the Stem Carefully!

Whenever a question states "Suggest two other causes...", re-read the stem to see what has already been mentioned. Any variation of the stem's cause (e.g. food competition) is automatically rejected by the examiner.