The heart works with/pumps blood. By the same substance-function link, the lungs work with which substance?

Introduction / Context:
We preserve the “organ ↔ characteristic substance” relation. The heart pumps blood; the lungs exchange gases, chiefly taking in oxygen for the body. Thus, the most specific parallel to “blood” is “oxygen”, the key substance handled by lungs during respiration.

Given Data / Assumptions:
We choose the specific substance analogous to blood.

Concept / Approach:
While “air” is inhaled, the functional target substance of lung exchange is oxygen (with carbon dioxide expelled). “Respiration” is a process, not a substance; “chest” is a location. Therefore “oxygen” mirrors the level of specificity of “blood”.

Step-by-Step Solution:

Verification / Alternative check:
Physiology texts describe alveolar gas exchange: O2 in, CO2 out. Selecting O2 keeps parity with the “blood” specificity.

Why Other Options Are Wrong:
Air: mixture, less specific; Respiration: process; Chest: location; Carbon dioxide: primarily expelled rather than taken up.

Common Pitfalls:
Picking “air” due to familiarity rather than the precise substance analogue.

Final Answer:
Oxygen