BitWithBite
Biology · Quick Reference
Lesson 8 — Respiratory System Cheat Sheet
In one line: Air travels nose → alveoli, where 70m² of thin, moist surface allows fast O2/CO2 exchange with capillaries.
Key Ideas
1Pathway. Nose/mouth → pharynx → larynx → trachea → bronchi → bronchioles → alveoli.
2Alveoli. 70m² surface area, wet, 1 cell thick, capillary-surrounded.
3Gas exchange. O2 alveoli→blood; CO2 blood→alveoli.
4Inspiration is active (diaphragm contracts); expiration is passive.
Lung Volumes
Tidal volume
500 mL (normal breath)
Vital capacity
4800 mL (max in/out)
Residual volume
1200 mL (always remains)
Alveolar surface area
70 m² (a tennis court)