Draw a labelled diagram of Escherichia coli as an example of a prokaryote.

Explain the process of transcription in prokaryotes.

Some prokaryotes cause infectious diseases which stimulate the body’s immune system. Outline the principles that form the basis of immunity.

Award [1] for each structure clearly drawn and correctly labeled.
cell wall; (with some thickness)
plasma membrane; (shown as single line or very thin)
cytoplasm;
pilus/pili; (shown as single lines coming from the cell wall)
flagellum/flagella; (thicker and longer than pili and embedded in cell wall)
70S ribosomes; (shown as small dots)
nucleoid / naked DNA;
approximate width 0.5 μm / approximate length 2.0 μm;              
Award [3 max] if the bacterium drawn does not have the shape of a bacillus (rounded-corner rectangle with length approximately twice its width).
Award [3 max] if any eukaryotic structures included.

transcription, synthesis of RNA identical to one strand/coding strand of DNA;
antisense stand acts as template/is transcribed;
RNA polymerase attaches to sequence of DNA known as promoter (region);
RNA polymerase separates the two strands of DNA;
(unwinding) exposes (10–20) DNA bases for pairing with RNA nucleotides;
RNA nucleotides matched to complementary bases;
adenine with uracil and cytosine with guanine / uracil replaces thymine;
H bonds between RNA nucleotide and complementary base on DNA strand;
(RNA) nucleoside triphosphates used;
hydrolysis of (two) phosphate molecules provides energy for reaction;
adds nucleotides to the 3′ end of RNA molecule/in 5′ → 3′ direction;
terminator is sequence of DNA signaling end of transcription;
RNA molecule separates completely from DNA;
Award any of the above points for a clearly drawn correctly annotated diagram.

skin and mucous membranes form barriers to pathogens as first line of defence;
macrophage recognizes antigens and ingests pathogen (in blood/body tissues);
presents antigen/MHC on cell surface;
macrophage activates helper T-cells that are complementary to antigen;
complementary B-cell becomes activated/stimulated by T-helper cells;
activated B-cell increases in size and divides by mitosis / creates clone of B-cells;
B-cells differentiate into plasma cells and memory cells; (both needed) plasma cells secrete specific antibodies;
memory cells remain/form basis of long-term immunity;
polyclonal response / multiple B-cells activated by different molecules of antigen;
Award any of the above points for a clearly drawn correctly annotated diagram.
(Plus up to [2] for quality)

Although the general level of diagrams has been improving, there were still a few poorly labelled ones, especially not distinguishing clearly between the cell wall and the plasma membrane. There were many pili and flagella seemingly floating in space, and many with eukaryotic structures. Most correctly drew the bacillus shape correctly.

Well prepared candidates gave a very clear and precise account of transcription. However some still remain confused between transcription, translation and replication, so described the wrong process. One common error was to say that helicase instead of RNA polymerase separated the strands. At the end, many forgot that they were explaining the process in prokaryotes and described the mRNA leaving the nucleus.

Most knew that the stimulation of the immune system involved macrophages, and T and B cells, but only the better candidates could explain the process clearly.