Unit 04 · The Respiratory System
Breathing looks simple until you measure it. This unit follows air from the airways through the bronchial tree to the alveoli, the muscles and pressure changes that move it in and out, the gas exchange that loads oxygen and unloads carbon dioxide at the alveolar wall, and the lung volumes you can put a number on with a spirometer. Mastery means you can measure your own lung volumes and defend what gas exchange is actually doing, not just label a diagram.
| Criterion | Not yet | Approaching | Mastered |
|---|---|---|---|
| Airways & the bronchial tree | Cannot name the major airways or order them from the trachea to the alveoli. | Names the airways but cannot trace the path air takes or say where cartilage gives way to smooth muscle. | Traces air from the trachea through bronchi and bronchioles to the alveoli on a model, and explains how each airway's structure fits its job. |
| Mechanics of breathing | Describes breathing as air being “sucked in” with no reference to muscles or pressure. | Names the diaphragm but cannot connect its movement to the pressure change that drives airflow. | Explains how the diaphragm and rib cage change thoracic volume and pressure, and predicts airflow direction from that pressure change. |
| Gas exchange & gas transport | Cannot say where or why oxygen and carbon dioxide move between air and blood. | Knows gas exchange happens at the alveoli but cannot explain diffusion by partial pressure, or how the blood carries each gas. | Explains gas exchange across the alveolar wall by partial-pressure differences and describes how oxygen and carbon dioxide are carried in the blood. |
| Lung volumes & control of breathing | Cannot distinguish tidal volume from vital capacity, or name what sets the breathing rate. | Defines the common lung volumes but cannot read them off a trace, or names the brainstem control only loosely. | Identifies tidal volume, vital capacity, and the reserve volumes on a spirogram, and explains how carbon-dioxide levels drive the control of breathing. |
| Lab technique (spirometry) | Cannot set up the spirometer or produce a usable trace. | Records a trace but mishandles the mouthpiece seal, reset, or reading of a volume. | Runs a clean spirometry trial, reads tidal volume and vital capacity off the trace, and interprets what the numbers mean. |
| Integration (cross-domain) | Treats the science as isolated facts; makes no cross-domain connection. | Names a link to history, reading, or writing but cannot defend why it matters. | Connects the unit to its anchor across History · Reading · Writing (plus chosen electives) and defends why the connection matters. |
“On my spirometry trace, the quiet in-and-out breaths are tidal volume; the big forced breath after a full inhale is vital capacity. Oxygen crosses into the blood at the alveoli because its partial pressure is higher in the air than in the capillary — it diffuses down that gradient.”
“You breathe in air and breathe out air. The lungs are for oxygen. Vital capacity is… how much you can breathe?”
You demonstrate this unit on Lab Day by measuring lung volumes on a spirometer and reading tidal volume and vital capacity off your own trace, then defending gas exchange aloud in an anatomy identification defense — not a multiple-choice test. A criterion counts as mastered only when you can both take the measurement at the bench and justify the physiology behind it. Mastery is demonstrated, not awarded.
A 5-page clipboard packet — unit overview, key terms, the mastery rubric, anchor examples, and a score sheet you can print and grade against.