10-2: Gas Exchange

Question 1

Gas exchange

Answer 1

-ventilation, gas exchange, circulation, cellular respiration
•Occurs by diffusion
• Partial pressure = the pressure of a particular gas in a
mixture of gasses
•Higher partial pressure to lower partial pressure
-Respiratory surface is the
part of animal body where
gasses are exchanged with
the environment (gills, skin,
lungs).

Question 2

exchange in gills

Answer 2

• Water = moist enough, but with not much oxygen
• Ventilation is the movement of water through fish’s mouth
and over its gills.
• Countercurrent exchange is the movement of blood in the
opposite direction of water movement in the gills.

Question 3

ventilation in gills

Answer 3

• movement of
  water through fish’s mouth and
  over its gills.

Question 4

Countercurrent exchange in gills

Answer 4

-Key principle:
• A concentration gradient over
the entire length of a capillary
maintains the partial pressure of oxygen in the water at any time slightly higher than in the
capillary.
-Key consequence:
• The oxygen diffuses into the
capillary with ease.

Question 5

Hemoglobin and the cooperative binding

Answer 5

• Respiratory pigments are proteins that transport oxygen, greatly increasing the
amount of oxygen that blood can carry.
• Hemoglobin -> protein that consists of 4 polypeptide chains -> heme -> iron ion -> oxygen molecule
• Hence, each hemoglobin molecule can bind up
to 4 oxygen molecules.
-Once one molecule of oxygen binds to one of its subunits, a
conformational change occurs in the protein, which causes the
remaining subunits much more likely to bind oxygen too.
This is termed cooperative binding

Question 6

Dissociation of oxygen from the hemoglobin

Answer 6

Different partial pressures of oxygen (PO2) are in different tissues
• This creates a diffusion gradient that unloads (dissociates) oxygen
from hemoglobin to the tissues.
• Lungs: PO2 is ~ 100 mm Hg; muscles at exercise: PO2 is ~ 30 mm Hg
• Oxygen-hemoglobin equilibrium curve -> pattern of O2 dissociating
from the hemoglobin

Question 7

oxygen-hemoglobin equilibrium curve

Answer 7

• Hemoglobin is a protein, and as such it is affected by a variety of factors, such as hydrogen ions.
• A drop in pH lowers the affinity of hemoglobin for O2 and this effect is called the Bohr shift: a drop in pH then shifts the oxygen dissociation
curve toward the right.
-Importance: hemoglobin is more likely to
release O2 during exercise to O2-deprived tissues.
• Another situation that reflects the affinity of hemoglobin for oxygen is
due to its different structure.
• A shift to the left is seen in the fetal hemoglobin structure.
Importance: fetal hemoglobin has higher affinity to oxygen,
compared to the mother’s hemoglobin.