Essays are structured around an introduction, body and conclusion, and the text itself is separated into paragraphs. See examples of the more formalised components of the essay, the introduction and the conclusion, in What does a good introduction look like? and What does a good conclusion look like?. The structure of an essay is not as formalised as that of a report. In some ways, you have more discretion about how you put your essay together, although you need to adhere to disciplinary expectations. Like reports, however, you must still provide an argument or position that is clearly sustained; that is, your reader must be able to follow what you have written. Refer to 'The reader – the writer' in How can I improve my argument? for more on this.
Studying for a biology exam? Stuck in bed with the flu and curious to find out what sort of microorganisms have made you so sick? While bacteria and viruses can both make you sick in similar ways, they are actually very different organisms with a wide range of differing qualities. Learning these differences can help you stay informed about any medical treatments you're undergoing and give you a better understanding of the complex biology that's going on inside you all the time. You can learn how to tell the difference between bacteria and viruses not only by learning the basics about them but also by examining them through a microscope and discovering more about their makeup and functions.