B3.1 Gas exchange

Question 1

B3.1.1—Gas exchange as a vital function in all organisms

Answer 1

Students should appreciate that the challenges become greater as organisms increase in size because
surface area-to-volume ratio decreases with increasing size, and the distance from the centre of an organism to its exterior increases.

Question 2

B3.1.2—Properties of gas-exchange surfaces

Answer 2

Include permeability, thin tissue layer, moisture and large surface area.

Question 3

B3.1.3—Maintenance of concentration gradients at exchange surfaces in animals

Answer 3

Include dense networks of blood vessels, continuous blood flow, and ventilation with air for lungs and
with water for gills

Question 4

B3.1.4—Adaptations of mammalian lungs for gas exchange

Answer 4

Limit to the alveolar lungs of a mammal. Adaptations should include the presence of surfactant, a
branched network of bronchioles, extensive capillary beds and a high surface area.

Question 5

B3.1.5—Ventilation of the lungs

Answer 5

Students should understand the role of the diaphragm, intercostal muscles, abdominal muscles and ribs.

Question 6

B3.1.6—Measurement of lung volumes
.

Answer 6

Application of skills: Students should make measurements to determine tidal volume, vital capacity, and
inspiratory and expiratory reserves

Question 7

B3.1.7—Adaptations for gas exchange in leaves

Answer 7

Leaf structure adaptations should include the waxy cuticle, epidermis, air spaces, spongy mesophyll,
stomatal guard cells and veins.

Question 8

B3.1.8—Distribution of tissues in a leaf

Answer 8

Students should be able to draw and label a plan diagram to show the distribution of tissues in a
transverse section of a dicotyledonous leaf.

Question 9

B3.1.9—Transpiration as a consequence of gas exchange in a leaf

Answer 9

Students should be aware of the factors affecting the rate of transpiration

Question 10

B3.1.10—Stomatal density

Answer 10

Application of skills: Students should use micrographs or perform leaf casts to determine stomatal
density.
NOS: Reliability of quantitative data is increased by repeating measurements. In this case, repeated counts
of the number of stomata visible in the field of view at high power illustrate the variability of biological
material and the need for replicate trials.

Question 11

B3.1.11—Adaptations of foetal and adult haemoglobin for the transport of oxygen

Answer 11

Include cooperative binding of oxygen to haem groups and allosteric binding of carbon dioxide

Question 12

B3.1.12—Bohr shift

Answer 12

Students should understand how an increase in carbon dioxide causes increased dissociation of oxygen
and the benefits of this for actively respiring tissues.

Question 13

B3.1.13—Oxygen dissociation curves as a means of representing the affinity of haemoglobin for oxygen at
different oxygen concentrations

Answer 13

Explain the S-shaped form of the curve in terms of cooperative binding.