B3.1  Gas Exchange

Guiding Questions:  
Guiding questions help students view the content of the syllabus through the conceptual lenses of both the themes and the levels of biological organization.

• How are multicellular organisms adapted to carry out gas exchange?
• What are the similarities and differences in gas exchange between a flowering plant and a mammal?

​​Linking Questions:  
Linking questions strengthen students’ understanding by making connections between topics.  The ideal outcome of the linking questions is networked knowledge.

• How do multicellular organisms solve the problem of access to materials for all their cells?
• What is the relationship between gas exchange and metabolic processes in cells?

Resources:

• At SHS, Topic B3.1 is taught in the Transport in Plants and Respiratory Gas Transport units. 
• Quizlet study set for this topic.  Coming soon!
• View the general sequence of the SHS course
• View the SHS units mapped to the IB Biology curriculum roadmap

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

• Define gas exchange.
• State the role of diffusion in gas exchange. 
• Explain the need for structures of larger organisms to maintain a large enough surface area for gas exchange.​

B3.1.2— Properties of gas-exchange surfaces.

• Outline the function of the following properties of gas-exchange surfaces:   permeability, thin tissue layer, moisture and large surface area.​

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

• State the reason why concentration gradients must be maintained at exchange surfaces.
• Explain dense networks of blood vessels, continuous blood flow, and ventilation with air for lungs and with water for gills as mechanisms for maintaining concentration gradients at exchange surfaces in animals.

B3.1.4— Adaptations of mammalian lungs for gas exchange.

• State the locations of gas exchange in humans.
• Outline the structures of mammalian lungs that are adapted to maximizing gas exchange.
• Draw a diagram showing the structure of an alveolus and an adjacent capillary.​

B3.1.5— Ventilation of the lungs.

• Identify the structure of the airway that connects the lungs to the outside of the body.
• Define ventilation, inspiration and expiration.
• State the relationship between gas pressure and volume.
• Outline the direction of movement of the diaphragm and thorax during inspiration and expiration.
• Outline the pressure and volume changes that occur during inspiration and expiration.​

B3.1.6- Measurement of lung volumes.

• Define tidal volume, vital capacity, and inspiratory and expiratory reserve.
• List methods for measuring tidal volume, vital capacity, and inspiratory and expiratory reserve.

B3.1.7— Adaptations for gas exchange in leaves.

• State the direction of movement of gasses exchanged in leaves.
• Outline adaptations for gas exchange in leaves, including  epidermis, waxy cuticle, stoma, guard cells, air spaces, spongy mesophyll, and veins.

B3.1.8- Distribution of tissues in a leaf.

• State that a plan diagram shows the distribution of tissues, but not individual cells. 
• Draw and label a plan diagram to show the distribution of tissues in a transverse section of a leaf.  Include upper and lower epidermis, palisade and spongy mesophyll, xylem and phloem.

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

• Define transpiration.
• Outline the relationship between water evaporation and transpiration. 
• Discuss the effect of abiotic factors on the rate of transpiration; including temperature and humidity.
• Discuss the advantages of opening and closing stomata at different times of day.

B3.1.10- Stomatal density.

• Calculate stomatal density from a leaf cast or micrograph. 
• Interpret micrographs or cast of leaf surfaces to compare stomatal density on different leaf surfaces.

AHL ​B3.1.11- Adaptations of fetal and adult hemoglobin for the transport of oxygen.

• Describe the structure and function of hemoglobin.
• Define affinity.
• Outline how cooperative binding alters hemoglobin's affinity for oxygen.
  
• Compare the oxygen affinity of adult and fetal hemoglobin.​

AHL B3.1.12- Bohr shift.

• Describe allosteric binding of CO2 to hemoglobin and the consequences for oxygen transport. 
• Define the Bohr shift. 
• Explain the mechanism and benefit of the Bohr shift.
• State the effect of the Bohr shift on the oxygen dissociation curve.

AHL B3.1.13- Oxygen dissociation curves as a means of representing the affinity of hemoglobin for oxygen at different oxygen concentrations.

• Define partial pressure.
• State the relative partial pressures of oxygen  in the atmosphere at sea level, in the alveoli, in alveoli blood capillaries, and in respiring tissue.
• Draw the oxygen dissociation curve to show affinity of hemoglobin for oxygen at different partial pressures of oxygen.
• Explain difference in the oxygen dissociation curves of adult and fetal hemoglobin.