IntroductionThe background section must provide the reader some context for understanding why you did the experiment. If it is on respiratory mechanisms, for example, tell why it is necessary for animals to develop respiratory structures. If the organism used is a goldfish, provide some relevant information on the biology of goldfish. Do not give away your findings yet. Include the genus and species names (the binomen) of the animals used (italicized always) at first mention, if they are known. Other taxonomic categories (Family, Order, etc.) are not necessary, but if mentioned, should be capitalized, but not underlined or italicized.
Hypothesis, objectives, or purpose all mean about the same thing. You must tell the reader what was intended with the study you are describing. This statement must be as clear as possible, which generally implies a single, well-constructed sentence. It is not a statement of methods--that comes next. Try to state your purpose elegantly. If you write, "The purpose of this study is to...", it will work, but it sounds very clunky.