Use alveolar and capillary evidence to explain how surface features and blood flow support efficient gas exchange in IB Biology HL B3.1.2.
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 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