Lecture #3

Question 1

Why is extracting O2 from water much more difficult than from air?

Answer 1

• relatively low O2 content to begin with in water compared to high O2 content in air
• highly variable in densely populated areas

Question 2

What factors affect O2 solubility in water?

Answer 2

• decreases with temperature and salinity

- saltier or hotter water holds less O2

Question 3

What are three strategies used by organisms to maximize O2 uptake, transport and delivery for aerobic metabolism? Relate it to Fick’s Law

Answer 3

1. thin respiratory epithelium
   - decrease X
2. large surface area of gills/lungs
   - increase SA
3. circulatory system adaptations (counter-current, blood pigments, takes O2 to tissues)
   - counter-current increases P1-P2

J = K * SA * (P1-P2) / X

Question 4

How does surface area scale compared to volume? What are the implications for gas exchange?

Answer 4

• does not scale linearly

- larger SA of larger organisms may not be able to take in enough oxygen

Question 5

How does a fish increase its respiratory surface area as it grows larger?

Answer 5

• invaginations (lungs) or evaginations (gills) increase surface area of respiratory organ
• gill arch divides into filaments then into lamella
• greater surface area of respiratory organ provides enough oxygen for the larger organism by keeping the SA/V ratio large enough

Question 6

What are Convection and Diffusion?

Answer 6

• convection: blood moving within the organism and transporting whatever is dissolved in it
• diffusion: gas moves following a partial pressure difference

Question 7

What are three characteristics of circulatory systems that maximize O2 delivery to tissues?

Answer 7

• Transfer O2 from the respiratory medium to blood
• Bring O2 to tissues
• Respiratory pigments that increase blood O2 carrying capacity

Question 8

Briefly describe “open”, “counter-current” and “tidal” gas exchange mechanisms.

Answer 8

Open: blood vessels are not organized, gradual equilibration between blood and water leading to ~50% in each
Tidal Gas Exchange: blood flows along respiratory surface in same direction as water, not exposed to whole ocean, just to the water inside the “pouch” of the respiratory organ, gives slightly more oxygen than open with blood containing ~55%
Counter-Current: blood and water flow in opposite directions so blood is always adjacent to water with greater amount of oxygen, causes it to diffuse into blood (maximizes partial pressure difference), gives highest O2 concentration of the three methods, ~75%

Question 9

Provide examples of animals that use “open”, “counter-current” and “tidal” gas exchange mechanisms.

Answer 9

Open: smaller organisms (larvae, small worms, zooplankton)
Tidal Gas Exchange: good for air-breathers, still used by sea cucumbers and the Fitzroy turtle (cloacal respiration)
Counter-Current: sharks, bony fish, very active fish, squids, crustaceans

Question 10

Be familiar with the following terms and their physiological significances: O2 affinity / dissociation curve (% saturation, P50 and its relationship with O2 affinity, right and left shifts, cooperativity.

Answer 10

• P50: the partial pressure of O2 required for 50% saturation of hemoglobin, low P50 means high affinity
• cooperativity: hemoglobin can bind 4 O2, binding the first one changes the shape and makes it more favorable to bind another one, causes non-linear relationship between pO2 and % Saturation
• right/left shifts: changing environmental factors can impact ease of binding to O2 and shift the affinity curve, changing P50
• left shift: higher affinity, lower temp, [H+], pCO2, P50
• right shift: lower affinity, higher temp, [H+], pCO2, P50