State one mechanism the ileum uses to absorb digested food into the bloodstream.

State the role of the hepatic portal vein.

Label the line that represents the ventricle.

Estimate the total time the atrioventricular valves are open.

Although some CO₂ entering the blood simply dissolves in the plasma, most enters the erythrocytes (red blood cells).

Outline how CO₂ interacts with hemoglobin once it enters erythrocytes.

Describe the formation of HCO₃^– in erythrocytes.

active transport/facilitated diffusion/endocytosis

transports blood from (capillaries of) small intestine to (capillaries/sinusoids of) liver

label should connect to solid line on graph.
Candidates should not use region with overlap of dotted and solid lines.

0.4 (s) (allow 0.38 to 0.43)

CO₂ attaches to protein portion (not Fe) in heme/carbaminohemoglobin formed;

a. CO₂ diffuses into erythrocytes;
b. joins water to form carbonic acid/H₂CO₃;
c. catalyzed by carbonic anhydrase (inside erythrocytes);
d. H₂CO₃ dissociates into H⁺ and HCO₃^–;

Many were able to state one mechanism for absorption used by the ileum with facilitated diffusion and active transport being most common. The most common incorrect response was microvilli.

Surprisingly the role of the hepatic portal vein was poorly understood by many.

Most could correctly identify the line on the graph representing ventricular pressure.

Even the better candidates struggled to use the graph correctly to find the total time the atrioventricular valves are open.

Very few answered this section correctly; instead many repeated what was required in section (ii). Few mentioned carbaminohemoglobin.

Many were able to get the 2 marks for describing the formation of hydrogencarbonate ions in erythrocytes, usually giving the correct equations.