Level 1 — RecognitionRespiratory System

Respiratory System

⏱ 20 minutes30 marksprintable — key stays hidden on paper

Level 1 Examination: Recognition

Time Limit: 20 minutes Total Marks: 30

Section A — Multiple Choice (1 mark each)

Choose the single best answer.

Q1. Which sequence correctly shows the pathway of air during inhalation?

A) Nose → larynx → pharynx → trachea → bronchi → alveoli
B) Nose → pharynx → larynx → trachea → bronchi → bronchioles → alveoli
C) Nose → trachea → pharynx → larynx → bronchioles → alveoli
D) Nose → pharynx → trachea → larynx → bronchi → alveoli

Q2. Gas exchange in the lungs occurs mainly at the:

A) Trachea
B) Bronchi
C) Alveoli
D) Larynx

Q3. During inhalation, the diaphragm:

A) Relaxes and moves upward
B) Contracts and moves downward
C) Stays still
D) Contracts and moves upward

Q4. During inhalation, the pressure inside the thoracic cavity (intrapulmonary pressure):

A) Increases above atmospheric pressure
B) Decreases below atmospheric pressure
C) Remains equal to atmospheric pressure
D) Becomes zero

Q5. The majority of carbon dioxide is transported in the blood as:

A) Dissolved CO $_2$ in plasma
B) Bound to haemoglobin (carbaminohaemoglobin)
C) Bicarbonate ions ( $\text{HCO}_3^-$ )
D) Carbonic acid crystals

Q6. Most oxygen is carried in the blood:

A) Dissolved in plasma
B) Bound to haemoglobin
C) As bicarbonate ions
D) Bound to white blood cells

Q7. The Bohr effect describes how haemoglobin's affinity for oxygen decreases when:

A) pH rises and CO $_2$ falls
B) pH falls and CO $_2$ rises
C) Temperature falls
D) Oxygen concentration rises

Q8. The main control centre that regulates breathing rate is located in the:

A) Cerebellum
B) Medulla oblongata
C) Hypothalamus
D) Spinal cord

Q9. Insects transport respiratory gases directly to their tissues using:

A) Gills
B) Lungs
C) Tracheae
D) Blood haemoglobin

Q10. The oxygen–haemoglobin dissociation curve is:

A) A straight line
B) S-shaped (sigmoidal)
C) Bell-shaped
D) Circular

Section B — Matching (1 mark each)

Q11–Q15. Match each structure/term (left) to its correct function/description (right).

#	Term		Description
11	Alveoli	A	Muscles that raise the rib cage during inhalation
12	External intercostals	B	Thin-walled sacs where gas exchange occurs
13	Epiglottis	C	Enzyme speeding conversion of CO $_2$ to bicarbonate
14	Carbonic anhydrase	D	Covers the trachea during swallowing
15	Gills	E	Respiratory surface of fish

Section C — True/False WITH Justification (2 marks each)

State True or False (1 mark) and give a one-line justification (1 mark).

Q16. Air pressure inside the lungs rises above atmospheric pressure during exhalation.

Q17. A shift of the oxygen–haemoglobin dissociation curve to the right means haemoglobin releases oxygen more easily.

Q18. The walls of the alveoli are thick to slow down gas exchange.

Q19. An increase in blood CO $_2$ concentration causes breathing rate to decrease.

Q20. Fish gills and insect tracheae both provide a large, moist surface area for gas exchange.

Answer keyMark scheme & solutions

Section A (10 marks)

Q1 — B (1 mark). Air travels nose → pharynx (throat) → larynx (voice box) → trachea → bronchi → bronchioles → alveoli. Larynx sits below the pharynx, ruling out A/D.

Q2 — C (1 mark). Alveoli are the terminal air sacs with thin walls and huge surface area — the actual site of exchange; larger airways are conducting passages only.

Q3 — B (1 mark). The diaphragm contracts and flattens (moves down), increasing thoracic volume.

Q4 — B (1 mark). Volume increases → pressure falls below atmospheric (Boyle's law), so air flows in.

Q5 — C (1 mark). ~70% of CO $_2$ is carried as bicarbonate ions; ~23% as carbaminohaemoglobin; ~7% dissolved.

Q6 — B (1 mark). ~98% of O $_2$ binds to haemoglobin; only a small fraction dissolves in plasma.

Q7 — B (1 mark). Lower pH (more H $^+$ ) and higher CO $_2$ reduce haemoglobin affinity for O $_2$ , promoting release at active tissues.

Q8 — B (1 mark). The medulla oblongata houses the respiratory control centre.

Q9 — C (1 mark). Insects use a network of tracheae delivering air directly to cells, not blood.

Q10 — B (1 mark). Cooperative binding gives the curve its sigmoidal (S) shape.

Q11 → B (1); Q12 → A (1); Q13 → D (1); Q14 → C (1); Q15 → E (1). Reasoning: Alveoli = exchange sacs; external intercostals raise ribs; epiglottis guards trachea during swallowing; carbonic anhydrase catalyses CO $_2$ →HCO $_3^-$ ; gills are fish respiratory surface.

Section C (10 marks)

Q16 — True (1). Justification (1): During exhalation muscles relax, thoracic volume decreases, so intrapulmonary pressure rises above atmospheric, pushing air out.

Q17 — True (1). Justification (1): A right shift lowers haemoglobin's O $_2$ affinity, so O $_2$ is offloaded to tissues more readily (Bohr effect).

Q18 — False (1). Justification (1): Alveolar walls are extremely thin (one cell thick) to give a short diffusion distance and rapid gas exchange.

Q19 — False (1). Justification (1): Rising CO $_2$ lowers blood pH; chemoreceptors signal the medulla to increase breathing rate to expel CO $_2$ .

Q20 — True (1). Justification (1): Both provide a large, thin, moist surface area maximising diffusion — though tracheae carry air internally rather than water.

Total: 30 marks

[
  {"claim":"CO2 transport percentages sum to 100 (bicarbonate 70 + carbamino 23 + dissolved 7)","code":"result = (70 + 23 + 7) == 100"},
  {"claim":"Oxygen bound to haemoglobin (~98%) exceeds dissolved fraction (~2%)","code":"hb=98; dissolved=2; result = (hb > dissolved) and (hb + dissolved == 100)"},
  {"claim":"Section A(10)+B(5)+C(10) equals total 30 marks","code":"result = (10*1 + 5*1 + 5*2) == 30"},
  {"claim":"Bohr effect direction: lower pH reduces affinity (modeled as affinity decreasing with H+)","code":"pH_low=7.2; pH_high=7.4; affinity = lambda ph: ph; result = affinity(pH_low) < affinity(pH_high)"}
]