Home / IB DP Biology- A3.2 Classification and cladistics -FA 2025- IB Style Questions For HL Paper 1

IB DP Biology- A3.2 Classification and cladistics -FA 2025- IB Style Questions For HL Paper 1

Question 

In a natural classification, what do all members of a genus have in common?
 
A. They all have the same binomial name.
 
B. They all belong to the same species.
 
C. They can freely interbreed to produce fertile offspring.
 
D. They have all evolved from the same common ancestor.

 

▶️Answer/Explanation

Answer: D

Explanation:

In biology, classification is based on the evolutionary relationships among organisms. The genus is a category that groups together species that are closely related. All species within a genus share a common evolutionary ancestor, meaning they have evolved from the same lineage.

Question

 What is a recognition feature for both of the plant phyla indicated?

▶️Answer/Explanation

Answer: D

 

Question

Which encircled area shows a clade?

▶️Answer/Explanation

Answer: C

Explanation: A clade is a group of organisms that includes:

  • a common ancestor
  • and ALL of its descendants

This is also called a monophyletic group in phylogenetics.

Let’s check each option:

Option A: Includes a common ancestor BUT not all its descendants. – NOT a clade

Option B: Looks like it’s picking only 2 tiny tips but doesn’t go back to the common ancestor that gave rise to all members of the group. – Not a clade either

Option C: Encloses a node (common ancestor) and includes all descendants of that node – Perfect clade definition

Option D: Odd shape… looks like it’s grouping species from different branches. Doesn’t trace back to a single common ancestor with all descendants – Not a clade

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