Transport of Oxygen The liquid part of the blood, the blood plasma, carries some O 2 in solution, but is limited (only 0.3mL of O 2 per 100mL plasma) This is not enough, so most animals contain molecules that can bind reversibly to O 2 In vertebrates O 2 transport molecule is hemoglobin contained in red blood cells Hemoglobin increases the capacity of blood to transport O 2 by about 60 fold

Hemoglobin A protein consisting of 4 polypetide subunits, each surrounding a heme group Heme group is an iron-containing ring structure that can bind a molecule of O 2

The availability of hemoglobin to pick up or release O 2 depends on the concentration of O 2, when it is high (such as in the lung capillaries) each molecule of hemoglobin can bind an O 2 molecule Carbon Monoxide binds to hemoglobin much easier (240 times!) So carbon monoxide prevents hemoglobin from transporting and releasing O 2 to tissues of the body The victim loses consciousness and can die because the brain lacks oxygen

Hemoglobin forms a loose chemical bond with O 2 which is easily given off whenever the concentration of O 2 around is low (at the tissue) Red blood cell → capillary cells → ECF → tissue cells

Transport of CO2 Ways of transporting CO 2 1. Dissolved in the water of blood plasma (small amount, about 7%) 2. Bound to hemoglobin (small amount, about 23%) 3. In form of bicarbonate ions (HCO 3 - ) in the blood plasma (most 70%)

When CO 2 dissolves in water, some of it reacts with water molecules to form carbonic acid (H 2 CO 3 ) Carbonic anhydrase in the red blood cells speeds up this reaction, which would normally occur at a slow rate Carbonic acid then breaks down into bicarbonate ion (HCO 3 - ) an hydrogen ion (H + )

When the concentration of H + in a solution increases, the pH is lowered Blood that is high in CO 2 has a pH lower than the norm of 7.4 The drop in pH causes the medulla oblongata to relay messages to the muscles (intercostals and diaphragm) to stimulate breathing Breathing helps to expel excess CO 2 and so restores the pH of the blood to normal See flowchart pg 296