The purpose of an introduction in scientific literature is to identify something scientists haven’t yet figured out, and offer a hypothetical explanation or answer to what is unknown. This hypothesis is what the whole paper is organized around. In your paper, think of the Introduction as posing a research question and a potential answer to that question. This answer is developed using logic and prior research related to the topic at hand. Introductions are NOT just random ‘background’; they are arguments. Use what you learned about making an argument and justifying your argument in the Composition class that you had to take.
Make sure that you reference (cite) prior work to support your argument. Any time you make a claim, a citation is needed. It is more important to cite claims than generic definitions. For example, a claim could be, “Protein structure is influenced by changes in pH”. This is different than a definition like: “Proteins are complex three-dimensional structures made of amino acids.