IB Biology HL B3.1 Gas Exchange Questions

Practise IB Biology HL B3.1 by linking respiratory surfaces and ventilation to oxygen transport, dissociation curves and transpiration evidence.

Exam points

Explain how lower oxygen partial pressure at high altitude reduces the diffusion gradient for gas exchange.
Relate alveolar area, thin walls, capillaries and surfactant to efficient gas exchange.
Trace ventilation muscles, thoracic pressure and airflow, interpreting pressure or spirometry data.
Calculate spirometric volumes and compare ventilation responses as exercise intensity increases.
Explain stomatal control, guard-cell responses and leaf adaptations that limit water loss.
Interpret leaf tissue distribution and internal air spaces as routes for light capture and gas diffusion.
Define transpiration, predict environmental water loss and evaluate potometer measurements.
Compare stomatal density and indicator patterns between leaf surfaces.
Explain haemoglobin subunits, haem binding, cooperative loading and fetal oxygen affinity.
Explain the Bohr shift from carbon dioxide and pH, predicting oxygen unloading from curve shifts.
Read oxygen dissociation curves for saturation, pO2, plateaus, cooperativity and relative affinity.

Covered syllabus points

B3.1.1—Gas exchange as vital function B3.1.2—Properties of gas-exchange surfaces B3.1.3—Maintaining concentration gradients B3.1.4—Mammalian lung adaptations B3.1.5—Lung ventilation B3.1.6—Lung volume measurements B3.1.7—Leaf gas exchange adaptations B3.1.8—Leaf tissue distribution B3.1.9—Transpiration B3.1.10—Stomatal density B3.1.11 (HL)—Haemoglobin adaptations B3.1.12 (HL)—Bohr shift B3.1.13 (HL)—Oxygen dissociation curves

[Maximum number: 7]

Adult humans may absorb more than five hundred litres of oxygen per day. Explain how gas exchange is maintained in the human respiratory system.

a. ventilation/inhaling brings fresh air/air with high oxygen concentration to the lungs OR ventilation/exhaling gets rid of stale air/air with high concentration of carbon dioxide

b. ventilation due to muscle contractions causing pressure/volume changes in the thorax

c. contraction of external intercostal muscles AND diaphragm occurs during inspiration OR contraction of internal intercostal muscles/abdomen wall muscles during «forced» expiration

d. alveoli surrounded by «many» capillaries

e. blood flow/pumping of heart «brings blood to/takes blood away from alveoli/lungs»

f. concentration gradients «of oxygen/ $\mathrm{CO}_{2}$ » maintained «by ventilation/blood flow»

g. $\mathrm{O}_{2}$ AND $\mathrm{CO}_{2}$ diffuse

h. $\quad \mathrm{CO}_{2}$ from capillaries/blood/vessel to alveolus/air AND $\mathrm{O}_{2}$ from alveoli into capillaries/blood/vessel

i. large numbers of alveoli increase surface area

j. short distance so rapid diffusion/gas exchange

k. type I pneumocytes/alveolus wall/capillary walls are one cell thick/very thin

l. alveoli «lining» moist for dissolving of gases/rapid diffusion OR

type II pneumocytes keep the «lining of» the alveolus moist

m. type II pneumocytes secrete surfactant to reduce surface tension/prevents alveoli from collapsing

[Maximum number: 3]

Carbon dioxide and oxygen are essential gases in many biological processes.

Describe conditions necessary in the lungs for efficient gas exchange in humans.

a. alveoli provide a large surface area (for easy diffusion of gases);

b. thin walls/ 1 -cell thick walls /type 1 pneumocytes/cells lining the alveoli are (extremely) thin (to facilitate gas exchange);

c. a moist surface on the cells (to dissolve the gases/oxygen and carbon dioxide);

d. type II pneumocytes secrete surfactant to reduce surface tension/prevent sides of alveolus sticking together;

e. blood capillaries have thin walls/1-cell thick walls (for short path/easy diffusion of gases);

f. good supply of blood / blood flow through capillaries around alveoli to maintain the concentration gradients of gases/ higher oxygen concentration in alveoli than in blood capillaries/ higher $\mathrm{CO}_{2}$ concentration in blood capillaries than in alveoli;

g. ventilation/breathing maintains concentration gradients of gases (between air in alveoli and blood capillaries) (to facilitate diffusion);

Mpb. Refers to thin walls, not membranes.

Mpd. Requires function of surfactant.

3 marks

[Maximum number: 3]

The graph shows the relationship between partial pressure of oxygen in air and altitude.

Explain the consequence of high altitude for gas exchange in humans.

a. lower oxygen partial pressure reduces oxygen availability (for the blood);

b. less oxygen diffuses/is exchanged with the blood OR less oxygen diffuses across the alveolar membrane/alveoli;

c. less saturation of hemoglobin with oxygen;

d. more $\mathrm{CO}_{2}$ remains in the blood OR less $\mathrm{CO}_{2}$ is exhaled;

e. breathing rate/depth is increased (in the short term);

f. (to compensate for the lack of oxygen) the body will produce more erythrocytes/RBCs/hemoglobin;

Mp a: Do not accept lower oxygen concentration at high altitude. Partial pressure must be mentioned.

Mp c: Do not accept increased hemoglobin affinity for oxygen instead of saturation.

Mp d: Allow higher $\mathrm{CO}_{2}$ decreasing hemoglobin affinity for oxygen.

Marking guidance:

3 max

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Covered syllabus points

Question 1

Question 2

Question 3