AQA GCSE Combined Science: Trilogy Biology Paper 2 (Higher), June 2025: Question 5

11 marks · Standard Demand difficulty · Short Answer

Answer questions on the adaptation, extinction, fossil formation, evolutionary study, and classification of plesiosaurs.

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Question

Question text

05 Plesiosaurs are extinct reptiles that lived in the ocean.

Figure 5 shows a fossil of a plesiosaur.

Figure 5

05.1 Plesiosaurs may have moved rapidly upwards to hold their heads above the water

surface to search for prey.

What type of adaptation was the rapid upwards movement?

[1 mark]

05.2 Give two biotic factors that may have caused the extinction of plesiosaurs.

[2 marks]

05.3 Describe how the plesiosaur fossil in Figure 5 could have been formed.

[3 marks]

05.4 Scientists use fossils to study evolution.

Suggest two reasons why scientists cannot study the mutations involved in the

evolution of plesiosaurs.

Do not refer to extinction in your answer.

[2 marks]

05.5 Table 1 shows part of the classification of a plesiosaur.

Complete Table 1.

[2 marks]

Table 1

Classification group Name

Domain

Kingdom Animalia

Chordata

Class Reptilia

Plesiosaur

Cryptoclididae

Genus Cryptoclidus

Species eurymerus

05.6 Give the binomial name of the plesiosaur in Table 1.

[1 mark]

Mark scheme

Show the mark scheme

Question 5

AO /

Question Answers Extra information Mark

Spec. Ref.

05.1 behaviour(al) allow functional 1 AO2

4.7.1.4

AO /

Spec. Ref.

ignore habitat

05.2 ignore competition unqualified

any two from: 2

AO1

allow hunters / poachers 4.6.3.3

• (new) predators

4.7.1.3

• (new) disease / pathogen allow named example

• competition for food allow lack of food

• lack of mates allow competition for mates

AO /

Spec. Ref.

allow skeleton or hard parts for

05.3 bones throughout

ignore compression

ignore reference to oxygen

(plesiosaur) died and sank (to 1 AO2

bottom of ocean / sea)

any two from: 2 AO1

• (plesiosaur died and) is do not accept plesiosaur (died

buried in sediment / sand / and) is buried in rock(s) 4.6.3.2

mud / silt

• (only) soft parts decayed /

eaten

bones were not decayed /

eaten

• bone(s) / remains replaced allow mineralisation of bones

by minerals allow bone(s) left imprint in mud

/ sand / sediment (that then

hardened to rock)

20 ignore bones turned to stone /

rock

AO /

Spec. Ref.

05.4 any two from: 2 AO2

4.6.2.1

• fossil record may be allow not all fossils have been

4.6.3.2

incomplete found

allow (some) fossils may have

been destroyed

allow there are not enough

fossils (to study)

• DNA will be destroyed by allow chromosomes / genes /

fossil formation alleles will be destroyed by fossil

formation

allow fossils do not contain DNA

/ chromosomes / genes / alleles

• no evidence of soft tissues

which are decomposed

(before fossilisation) 21

• only able to study phenotype allow only able to study

(from fossils) observable characteristics (of

bones / skeleton)

AO /

Spec. Ref.

05.5 2 marks for 4 correct 2 AO1

Classification Name 1 mark for 2 or 3 correct AO2

group No marks for 1 correct 4.6.4

eukaryota /

eukaryote(s)

phylum / phyla

order

family

ignore italics and upper / lower

case letters

AO /

Spec. Ref.

05.6 Cryptoclidus eurymerus ignore italics and upper / lower 1 AO2

22 case letters 4.6.4

do not accept

Cryptoclididae eurymerus

Total Question 5 11

How to answer it

Plesiosaurs: Adaptations, Fossilisation & Classification

WHAT THIS QUESTION TESTS

This question evaluates fundamental knowledge across Ecology and Inheritance, Variation and Evolution:

Categorising types of adaptations (structural, behavioural, functional).
Distinguishing biotic factors from abiotic factors in extinction events.
Sequencing the stages of mineralised fossil formation.
Evaluating the limitations of the fossil record regarding genetic material and evolutionary evidence.
Recalling the hierarchy of the Linnaean classification system and Carl Woese's three-domain model.
Identifying the correct binomial naming format from tabular data.

QUESTION 05.1 • 1 MARK

Type of Adaptation

Identifying an organism's adaptation category based on observed actions

✅ Correct Answer

Behavioural (allow functional)

💡 Key Knowledge

Structural: Physical body features (e.g., flippers, sharp teeth).
Behavioural: An action or way an organism acts/moves (e.g., moving upwards to hunt).
Functional: Internal biochemical or physiological processes (e.g., producing venom, holding breath).

Mark Scheme Note: 1 mark for behaviour(al) . The question describes an active movement ("rapid upwards movement"), which represents a clear action.

QUESTION 05.2 • 2 MARKS

Biotic Factors Causing Extinction

Suggesting two living factors that could wipe out a marine species

✅ Correct Answers (Any two)

(New) predators
(New) disease / pathogen
Competition for food (or lack of food)
Lack of mates (or competition for mates)

❌ Common Errors

Listing abiotic factors: Writing asteroid impact, volcanic eruption, or temperature/climate change. These are non-living.
Vague statements: Writing just competition without stating what they competed for (food/mates).
Mentioning "habitat loss" unqualified (loss of physical space is treated as abiotic).

Examiner Insight: Always highlight the word biotic in exam stems. Biotic = living factors. Abiotic = non-living factors.

QUESTION 05.3 • 3 MARKS

Fossil Formation Process

Step-by-step description of mineralised fossil creation

✅ Correct Description (3 Marks)

The plesiosaur died and sank to the bottom of the sea/ocean. [1 mark]
It was rapidly covered / buried in sediment (mud / sand / silt). [1 mark]
The soft tissues decayed (or were eaten), and the bones were replaced by minerals (mineralisation) over millions of years. [1 mark]

🧠 Exam Technique: The Chronological Story

Structure your fossilisation response as a sequence of time:

Event 1: Death & sinking to seabed.
Event 2: Burial under layers of sediment (preventing scavengers).
Event 3: Flesh rots away; hard parts (bones) are infiltrated and replaced by dissolved minerals as sediment turns to rock.

❌ Common Pitfalls in This Question

Do NOT write: "Buried in rock." It gets buried in sediment, mud, or silt which later compacts into rock over geological time. Avoid saying "bones turned to rock" without explaining that minerals replaced the bone.

Mark Scheme Breakdown: 1 mark for dying and sinking to sea floor; 2 marks for any two of: buried in sediment / soft parts decayed leaving hard bones / bones replaced by minerals.

QUESTION 05.4 • 2 MARKS

Limitations of Fossils in Studying Mutations

Explaining why genetic changes cannot be read directly from ancient rocks

✅ Correct Reasons (Any two)

DNA / genes / chromosomes are destroyed or broken down during fossilisation.
The fossil record is incomplete (many fossils destroyed, not formed, or undiscovered).
Soft tissues decompose, leaving no genetic material or cellular structures.
Scientists can only observe the phenotype / skeletal anatomy, not the genotype.

🧠 Exam Technique: Follow Negative Constraints!

The question strictly states: "Do not refer to extinction in your answer."

Writing "because plesiosaurs are extinct" immediately scores 0 marks. Focus purely on what fossils actually preserve: hardened mineral casts of skeletons, never intact nucleic acids.

Examiner Insight: Mutations occur in DNA base sequences. Because fossils are mineralised rock replicas of hard tissues, original organic DNA does not survive across millions of years.

QUESTION 05.5 • 2 MARKS

Completing the Classification Hierarchy

Using the Linnaean system and Three-Domain model

Classification Group	Name in Table 1	Notes & Recall Tip
Domain	Eukaryota / eukaryote(s)	Animals have membrane-bound nuclei
Kingdom	Animalia	Given in table
Phylum	Chordata	Organisms with a backbone / nerve cord
Class	Reptilia	Given in table
Order	Plesiosaur	Comes between Class and Family
Family	Cryptoclididae	Comes between Order and Genus
Genus	Cryptoclidus	Given in table
Species	eurymerus	Given in table

💡 Mnemonic for Classification

Remember Carl Linnaeus's hierarchy + Carl Woese's Domain:

Dear King Philip Came Over For Good Soup

Domain → Kingdom → Phylum → Class → Order → Family → Genus → Species

📐 Marking Grid

4 correct: 2 marks
2 or 3 correct: 1 mark
0 or 1 correct: 0 marks

QUESTION 05.6 • 1 MARK

The Binomial Name

Writing the formal scientific name from classification data

✅ Correct Answer

Cryptoclidus eurymerus

💡 Key Rule: Binomial System

Every organism's scientific name consists of two parts:

Genus: First word, capitalised ( Cryptoclidus ).
Species: Second word, lower case ( eurymerus ).

❌ Mark Scheme Trap

Do NOT write: Cryptoclididae eurymerus . Cryptoclididae is the family, not the genus! Always take the last two rows: Genus + Species.

Extra Information: The examiner will ignore italics and capitalization errors for this 1 mark, provided the correct two words are combined in order.

Topics

Biology · B6: Inheritance, Variation and Evolution · B7: Ecology

Question and mark scheme from the AQA GCSE Combined Science: Trilogy examination, Biology Paper 2 (Higher), June 2025. QuestionVault is an independent revision resource; questions remain the copyright of the awarding body.