Q23 a) Use an example to explain why hybridisation within a species is carried out.Hybridisation, the deliberate cross breeding within a species is performed to benefit society. The use of a pedigree to ensure that the favourable characteristics of a species are produced in the offspring, such as heightened muscle growth in horses is a clear advantage to the use of hybridisation. B) Use an example of a named transgenic species to discuss the social and environmental impact of this technology.Transgenic species, the deliberate cross between two foreign species provides benefits and disadvantages to society. For example, the injection of a specific growth hormone into the red salmon assists the production of the species, allowing for a greater population source. This consequentially provides an economical benefit in the reduction of red salmon prices, being of immense benefit to society. Contrastingly, the introduction of the growth hormone into the red salmon severely reduces the genetic diversity within the species. Furthermore, the ecosystem may be disrupted by the increased spread of genetically enhanced red salmon, removing the natural food chain of a balanced environment. As a result, transgenic species introduce a variety of social and environmental impacts on societyQ28) a) Marker B Cellsb) The model is extremely effective in explaining the cause of organ rejection in a transplant recipient, depicting the differences in marker cells between the host and donor T-cells. By using different shapes to clearly portray the T-cells, it is evident that the immune system of the recipient is able to easily identify the foreign cell, which effectively becomes an antigen that sparks the immune response and subsequent organ rejection. c) The helper-T cell and cytotoxic T-cell are the fundamental T lymphocytes which control the recipients immune response to organ rejection. The helper T-cells initially recognise the foreign donor cells, stimulating the production of cytotoxic T-cells asnd attaching onto the marker cells. Furthermore, the cytotoxic T-cells attack the foreign donor cells identified by the helper T-cells, resulting in organ rejection.