10 NEET Traps with Corrections
TRAP 1: RV vs FRC Confusion
- Wrong: "RV is the air remaining after a normal expiration."
- Correct: RV is the air remaining after MAXIMUM FORCED expiration. After a NORMAL expiration, the remaining air is FRC (= ERV + RV). RV < FRC always.
TRAP 2: VC includes RV
- Wrong: "VC = TV + IRV + ERV + RV"
- Correct: VC = TV + IRV + ERV. RV is excluded because it CANNOT be voluntarily expelled. Adding RV gives TLC, not VC.
TRAP 3: CO2 primary transport form = carbaminohaemoglobin
- Wrong: "Most CO2 is transported as carbaminohaemoglobin because CO2 binds Hb."
- Correct: 70% of CO2 is HCO3– (bicarbonate). Carbaminohaemoglobin = only 23%. Students confuse "CO2 binds Hb" with "this is the primary form."
TRAP 4: Quiet expiration is active
- Wrong: "Expiration always requires active muscle contraction."
- Correct: QUIET expiration is PASSIVE (elastic recoil only; no muscles contract). Only FORCED expiration is active (internal intercostals + abdominals).
TRAP 5: Right shift = more O2 retained by Hb
- Wrong: "A right-shifted O2–Hb curve means Hb holds O2 more strongly."
- Correct: Right shift = LOWER O2 affinity → MORE O2 released to tissues. Left shift = higher affinity → O2 retained.
TRAP 6: Pneumotaxic centre prolongs inspiration
- Wrong: "The pneumotaxic centre in the pons promotes deep, prolonged inspiration."
- Correct: Pneumotaxic centre INHIBITS inspiration, limiting its duration. Medullary rhythmicity centre initiates breathing.
TRAP 7: Cl– moves out during chloride shift
- Wrong: "During the chloride shift, Cl– moves out of RBCs as HCO3– moves in."
- Correct: HCO3– moves OUT of RBCs to plasma; Cl– moves IN to maintain electrical neutrality.
TRAP 8: Both lungs have 3 lobes
- Wrong: "Both lungs have 3 lobes each."
- Correct: Right = 3 lobes; Left = 2 lobes (because of the cardiac notch).
TRAP 9: O2 gradient at alveoli is small
- Wrong: "The pO2 gradient between alveoli and blood is 5 mmHg (like CO2)."
- Correct: O2 gradient = 104 – 40 = 64 mmHg (large). CO2 gradient = 45 – 40 = 5 mmHg (small). Don't confuse the numbers.
TRAP 10: Carbonic anhydrase acts on the alveolar surface
- Wrong: "Carbonic anhydrase on alveolar epithelium converts CO2 to HCO3–."
- Correct: Carbonic anhydrase is inside RBCs (not on alveolar surface). It acts intracellularly in erythrocytes.