Blood clotting involves a cascade of reactions. Which statement describes the blood-clotting process?

A. Red blood cells release clotting factors that result in the production of fibrin.

B. Clotting factors trigger the conversion of the inactive thrombin to prothrombin.

C. Insoluble fibrinogen is converted into soluble fibrin.

D. Fibrin forms a mesh that traps platelets and blood cells.

D

About half of candidates answered this question correctly, but the discrimination index was rather low. Answer D was clearly correct, but many candidates chose A or B instead. A was incorrect because red blood cells do not release clotting factors. B was incorrect because thrombin is not converted to prothrombin. As ever, candidates are advised to read all the possible choices.

What is produced by type II pneumocytes?

A. Epinephrine

B. Elastase

C. Pulmonary surfactant

D. Alpha 1-antitrypsin

C

Which structural feature enables saltatory conduction?

A. Nodes of Ranvier between Schwann cells

B. Na⁺ channels under Schwann cells

C. K⁺ channels under Schwann cells

D. Sodium–potassium pumps under Schwann cells

A

Some strains of the pathogenic bacterium Staphylococcus aureus have developed mechanisms that protect them against foreign DNA. What effect does this have on the evolution of antibiotic resistance in these strains of S. aureus?

A. Slower evolution, as bacteria with the antibiotic resistance gene will not reproduce

B. Slower evolution, as the antibiotic resistance gene from other species will not be accepted

C. Faster evolution, as mutations within a population are less likely to occur

D. Faster evolution, as antibiotic resistance genes can only be passed to individuals of the same species

B

Answered correctly by 50 % of the candidates that understood that by not accepting the antibiotic resistance gene, Staphylococcus aureus will be slow to develop resistance to the antibiotic.

The graph shows the changing membrane potential during a nerve impulse. Which letter indicates when the potassium channels open?

C