The third paragraph of the body should contain the weakest argument, weakest example, weakest illustration, or an obvious follow up to the second paragraph in the body. The first sentence of this paragraph should include the reverse hook which ties in with the transitional hook at the end of the second paragraph. The topic for this paragraph should be in the first or second sentence. This topic should relate to the thesis statement in the introductory paragraph. The last sentence in this paragraph should include a transitional concluding hook that signals the reader that this is the final major point being made in this paper. This hook also leads into the last, or concluding, paragraph.
Although the conclusion paragraph comes at the end of your essay it should not be seen as an afterthought. As the final paragraph is represents your last chance to make your case and, as such, should follow an extremely rigid format.
If you want to get better idea of what the peculiarities of writing in this subject field are, feel free to consult our Natural sciences section.