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.
- Syllabus
- First assessment 2025
- Course
- Biology HL
- Level
- HL
Exam points
- link surface area, diffusion distance, permeability and moisture to efficient gas exchange
- explain how ventilation and blood flow maintain oxygen and carbon-dioxide gradients
- interpret spirometry and pressure-volume changes during inspiration and expiration
- explain stomatal control, leaf adaptations and environmental effects on transpiration
- interpret oxygen dissociation curves, cooperative binding and Bohr shifts to predict oxygen loading and unloading
Covered syllabus points
B3.1.1—Gas exchange as vital functionB3.1.2—Properties of gas-exchange surfacesB3.1.3—Maintaining concentration gradientsB3.1.4—Mammalian lung adaptationsB3.1.5—Lung ventilationB3.1.6—Lung volume measurementsB3.1.7—Leaf gas exchange adaptationsB3.1.8—Leaf tissue distributionB3.1.9—TranspirationB3.1.10—Stomatal densityB3.1.11 (HL)—Haemoglobin adaptationsB3.1.12 (HL)—Bohr shiftB3.1.13 (HL)—Oxygen dissociation curves
Learn this topic
Question 1
[Maximum number: 3]
Outline the process of gas exchange necessary for aerobic respiration in a unicellular eukaryotic organism.
| a | oxygen must be taken up AND carbon dioxide must be released |
| b | gases pass through a cell membrane by simple diffusion |
| c | require a concentration gradient; OR pass from high concentration to low concentration |
| d | without requiring energy; OR passive process |
| e | large SA: vol ratio |
Question 2
[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 CO2 concentration in blood capillaries that 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
Question 3
[Maximum number: 14]
Question (a)
(a)
A supply of oxygen is needed for aerobic respiration in mitochondria. Describe the features of alveoli in human lungs that adapt them for efficient absorption of oxygen.
[ 6 ]
large surface area from having many alveoli;
single/flattened layer of (thin) cells in wall;
(surrounded by) dense network of capillaries/capillary bed;
short distance for gases/oxygen/carbon dioxide to diffuse;
moist lining / film of moisture on inside of alveolus;
moisture allows oxygen/gases to dissolve;
diffusion of oxygen down concentration gradient;
Question (b)
(b)
Explain the mechanism of ventilation of human lungs.
[ 8 ]
ventilation is movement of air into and out of lungs;
volume of thorax/lungs/chest increased/decreased;
pressure in thorax/lungs/chest decreased/increased;
air flows from higher to lower pressure / air flows until the pressures are equal;
During inspiration/inhalation:
external intercostal muscles contract so ribcage moved up/out;
diaphragm contracts so moves down/becomes flatter;
internal intercostal/abdomen (wall) muscles relax;
During expiration/exhalation:
external intercostal muscles relax so ribcage moved down/in;
diaphragm relaxes;
recoil of elastic fibres that stretched during inspiration;
internal intercostal muscles contract (during forced ventilation);
abdomen (wall) muscles contract (during forced ventilation);
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