Outline reasons for the therapeutic use of stem cells.

Describe how monoclonal antibodies are produced.

Explain the role of the electron transport chain in the generation of ATP by cell respiration.

1. unspecialized/undifferentiated stem cells can divide/differentiate along different pathways;
2. (stem cells are accessible as they) come from embryos/bone marrow/umbilical cord blood/adult tissue;
3. (stem cells) can regenerate/repair/regrow diseased/damaged tissues in people;
4. valid specific example;
5. drugs can be tested on stem cells (in laboratories to see if they are harmful);

1. mice/rabbit/small mammal injected with one type of antigen;
2. cells from the spleen/antibody-producing cells are removed;
3. plasma cells that produce antibodies (are used);
4. myeloma/tumor cells that divide endlessly (are used);
5. fusion of plasma cells with tumor/myeloma cells / fusion produces hybridoma cells;
6. selection of hybridoma cells / medium used that only allows growth of hybridoma cells;
7. fused cells/hybridoma cells are cultured/grown in tissue culture/grown in a fermenter;
8. (hybridoma) cells divide endlessly and produce the desired antibodies;

1. electron transport chain performs chemiosmosis / chemiosmosis generates ATP;
2. receives energy/electrons from oxidation reactions/from Krebs cycle/glycolysis;
3. receives electrons from reduced NAD/NADH/reduced FAD/FADH;
4. energy released as electrons pass from carrier to carrier (in the chain);
5. release of energy (from electron flow) coupled to proton pumping;
6. protons pumped into intermembrane space;
7. creates proton gradient;
8. protons diffuse back/move down the concentration gradient (across membrane);
9. protons pass through ATP synthase;
10. protons return to the matrix;
11. flow of protons provides energy for generating ATP;
12. electrons transferred to oxygen at end of electron transport chain;

Most candidates knew something of the therapeutic uses of stem cells, including differentiation for specific roles. There was a tendency for over-optimism over what can be fixed using stem cells. For example, stem cells are not a treatment for most cancers. The best answers stuck to well-established procedures such as the treatments for leukaemia using stem cells from bone marrow.

Production of monoclonal antibodies was not widely understood and the mean mark was below 1 (out of 5). Many answers described the normal immune response by the body that results in production of antibodies, rather than the production of hybridoma cells that allow large-scale antibody manufacture.

For well-prepared candidates this question posed no difficulty and there were some excellent detailed accounts of chemiosmosis. The discrimination index was the highest for any question on the paper, indicating that there was no room for lucky guesses about the biology here!