Draw a labelled diagram to show the ultrastructure of Escherichia coli.

Distinguish between active and passive movements of materials across plasma membranes, using named examples.

Explain how chemiosmosis assists in ATP production during oxidative phosphorylation.

Award [1] for each structure clearly drawn and correctly labelled.

cell wall – with some thickness;

plasma membrane – shown as single line or very thin;

cytoplasm; pilus/pili – shown as single lines;

flagellum/flagella – shown as thicker and longer structures than pili and embedded in cell wall;

70S ribosomes; nucleoid / naked DNA;

approximate width 0.5 μm / approximate length 2.0 μm;

Award [4 max] if the bacterium drawn does not have the shape of a bacillum (rounded-corner rectangle with length approximately twice its width).

Award [4 max] if any eukaryotic structures included.

Both the passive and active movements must be contrasted to receive a mark. Award [3 max] if no examples are given. Responses do not need to be shown in a table format.

occurs during aerobic respiration;

oxidative phosphorylation occurs during the electron transport chain;

hydrogen/electrons are passed between carriers;

releasing energy;

finally join with oxygen (to produce water);

occurs in cristae of mitochondria;

chemiosmosis is the movement of protons/hydrogen ions;

protons move/are moved against their concentration gradient;

into the space between the two membranes;

protons flow back to the matrix;

through the ATP synthase/synthetase (enzyme);

energy is released which produces more ATP/combines ADP and Pi;

Most of the diagrams were of a pleasing standard. Marks were lost by drawing an oblong rather than a bacillus shape, including eukaryotic organelles and showing the flagellum as an extension of the cell wall, rather than embedded within it.

In a “distinguish” question, points should be contrasted, rather than writing about passive movement and then active movement.

There were a few comments from the G2 forms about the difficulty of gaining nine marking points. Better candidates obtained these with ease. Many of the better candidates' answers incorporated clear, annotated diagrams. Weaker candidates tried to use half-remembered diagrams without any explanation and failed to gain many marks.