Analogy — Chlorophyll : Plant :: Haemoglobin : ? Choose the biological counterpart carried within living organisms that parallels chlorophyll in plants.

Introduction / Context:
Chlorophyll is a characteristic pigment associated with plants; it enables photosynthesis. In a similar structural mapping, haemoglobin is the characteristic oxygen-carrying protein associated with blood in animals, particularly vertebrates. The analogy therefore pairs the biological substance with its primary biological milieu.

Given Data / Assumptions:

• Chlorophyll ↔ plant tissues (chloroplasts), defining association.
• Haemoglobin ↔ blood (in red blood cells), defining association.
• We seek the domain/body in which haemoglobin normally resides.

Concept / Approach:
Maintain “substance : natural locus” structure. Chlorophyll is not “photosynthesis,” but a pigment found in plants; likewise haemoglobin is not “oxygen” (which it carries) nor “red” (a color), but a protein in blood. Hence, “blood” mirrors “plant” as the locus for haemoglobin.

Step-by-Step Solution:

Verification / Alternative check:
Biology basics: haemoglobin within erythrocytes binds oxygen for transport; its presence colors blood red in most vertebrates.

Why Other Options Are Wrong:

• Haemorrhage — bleeding event, not a locus.
• Oxygen — transported by haemoglobin, not the container/location.
• Red — color attribute, not the biological medium.

Common Pitfalls:
Choosing a function/object (oxygen) or attribute (red) rather than the hosting medium (blood), which is required to match the first pair’s logic.

Final Answer:
Blood