Draw a labelled diagram of a prokaryotic cell.

Outline transcription in prokaryotes.

Some prokaryotes cause infectious disease in humans. Explain the principles of vaccination.

Award [1] for each structure clearly drawn and correctly labelled, up to [4 max].
a. cell wall – a uniformly thick wall;
b. pili – hair-like structures connected to cell wall / flagellum – at least length of the cell;
c. plasma/cell membrane – represented by a continuous single line; (may be labelled as the innermost wall line)
d. ribosomes (70S) – drawn as small discrete dots;
e. naked DNA/nucleoid – region with DNA not enclosed in membrane;
f. plasmid – circular ring of DNA;
g. cytoplasm – the non-structural material within the cell;
Award [2 max] if any eukaryotic structure is shown.

a. transcription is the copying of a strand of DNA into RNA/RNA formation;
b. RNA polymerase binds to promoter region of DNA;
c. anti-sense strand as template / only one strand copied;
d. RNA polymerase unwinds DNA/separates the strands;
e. RNA nucleotides/nucleoside triphosphates pair with complementary bases on DNA;
f. Adenine to Thymine, Cytosine to Guanine, and Uracil to Adenine; (do not accept letters alone)
g. added at 3' end / strand grows 5' to 3' ;
h. RNA nucleotides joined with covalent/sugar-phosphate bonds;
i. RNA polymerase separates from DNA when reaches terminator/termination sequence;
j. no introns/post-transcriptional modification/RNA splicing (as occurs in eukaryotes);

a. vaccines contain a dead/weakened form of the pathogen/bacteria/virus;
b. vaccine introduced to the body by injection/on surface of skin/orally;
c. antigens in the vaccine cause antibody production;
d. antigen/pathogen engulfed by macrophage/phagocyte;
e. each type of lymphocyte recognizes specific antigen;
f. macrophages activate helper T-cells;
g. which activate B-cells;
h. B-cells divide to form clones/memory cells;
i. B-cells divide to form plasma cells/antibody producing cells;
j. result is (specific) immunity;
k. vaccination/first exposure causes slow production of antibodies and lower level of antibodies; (this idea can be illustrated on a diagram or graph)
l. contact with the disease leads to rapid production and higher level of antibodies; (this idea can be illustrated on a diagram or graph)
m. second/booster shot to stimulate memory cells/more production of antibodies;

Overall, candidates performed very well on this question.  

The diagram in 5a was well drawn by most. A number of students included eukaryotic structures in their drawings. Flagella were often drawn too short in relation to the overall length of the cell. Pilli were often poorly drawn being shown not connected to the cell. The diameter of ribosomes was often too large in relation to the rest of cell structures.

Overall, candidates performed very well on this question.  

Many were able to outline transcription successfully. Some confused transcription with replication. A number referred to helicase as the enzyme responsible for separating and unwinding the helix.

Overall, candidates performed very well on this question.  

Most scored well on part c of the question. An area of misunderstanding surrounds what happens upon second exposure to the antigen.  It should be noted that antibodies are produced more rapidly and to a higher level.