List two functions of membrane proteins.

Explain why digestion of large food molecules is essential.

Outline why antibiotics are effective against bacteria but not against viruses.

Outline the use of polymerase chain reaction (PCR) to copy and amplify minute quantities of DNA.

a. hormone binding sites / receptors;

b. (immobilized) enzymes;

c. cell adhesion;

d. cell (to cell) communication;

e. passive transport/channels;

f. active transport/pumps;

g. facilitate diffusion;

h. carry electrons;

a. many molecules are too large to be absorbed (by the villi) / small molecules are soluble and can be absorbed;

b. large food molecules are broken down so they can be reorganized/rearranged;

a. antibiotics block/inhibit specific metabolic pathways/cell functions found in bacteria;

Accept specific examples of inhibition such as cell protein synthesis, cell wall formation

b. viruses must use host/eukaryotic cell metabolism / viruses do not have their own metabolic pathways;

c. host/eukaryotic cell metabolism/pathways not blocked/inhibited by antibiotics;

a. strands of DNA (fragments) split/denatured with heat;

b. complementary nucleotides added to split stands (when cooling);

c. with the use of (DNA) polymerase (and primers);

d. process/heating and cooling cycle is repeated (until enough DNA is obtained);

Accept example of PCR application e.g. paternity cases or forensic investigations.

Functions were asked for, not named structures. “Channels” and “pumps” by themselves were too vague to gain marks.

The idea of food breakdown to a small enough size for absorption was the easier mark achieved by many. Some candidates wrote that food had to be “digested” but “digestion” was written in the stem of the question and too vague for credit.

The idea of food breakdown for eventual reorganization/rearrangement rarely appeared in any answer, perhaps indicating a conceptual gap in candidate understanding of digestion.

There was a complete misunderstanding of this question. Almost no candidate seemed to realize that the question was asking for how the PCR can copy and amplify minute quantities of DNA. Thus, the process was either unknown or ignored so marking points were immediately lost. In contrast, almost every candidate knew forensic science as a use of PCR, thereby salvaging one mark.