You need to provide enough information for your reader (and you) to understand your project and its importance. You can assume your reader has a general scientific background in the discipline (so may assume they already understand everything that would be covered in a college introductory level course). For example, if you did a project on whether homemade sunscreens can protect against UV light induced DNA damage, you might want to include background information on how sunscreen is thought to protect against UV light (what components in sunscreens protect against damage and how) but would not need to explain why damage to DNA is detrimental to cells. The background information needed various for every research question and project but below are some questions to help guide you towards the background information you may need to include when presenting your work.

What is your big research question and why is it important? If your project relates to cancer you might want to include some information on how many people get certain types of cancer each year, death rates, detection, etc. If your project relates to obesity you may want to include statistics on obesity rates, how they vary by diet or geographical regions, detrimental effects of obesity, etc. If your project relates to global warming you may want to include information on temperature predictions, main causes of global warming, etc. In general, use background information to help your reader understand the prevalence, implications, and challenges of your big question to back up the importance of your research.

What materials are you using in your experiments? If you are using mutant strains of anything you will usually want to explain the mutations in terms of what genes and pathways are affected and what phenotypes the mutations cause. If you are using an unusual chemical or substance in your experiment you may want to include information on the relevant properties of those materials (i.e. why you are using it). For example, if you are using a chemical to induce mutations you should make sure your reader knows that the chemical will mutate DNA. If you are using a particular type of bacteria that is pathogenic to your model organism you should include that information.

Is your experimental or model system unusual? If you are using a common model organism in your experiments you do not need to provide background on the system (you can assume your reader would already be familiar with common model organisms such as mice, S. cerevisiae, E. coli, fruit flies, C. elegans, zebrafish and Xenopus laevis). However, if your model system is not standard (perhaps a particular human cell culture line or bean beetle) you should include basic information on the system.

What related work has previously been done? Before doing an experiment scientists scour the published literature to find previous work that has been done in the research area. When you find related work you should describe to your reader what has already been done and what is the current understanding in the field. Has someone done a similar experiment but in a different model organism? Has someone studied the same mutant before but using a different assay or phenotype? Have people studied other materials but not the one you will use? Has your experiment been done before? Do people have predictions for how the mechanism you are studying work? You cannot report on all the related work that has been done (remember you need to be concise in science presentations) so you will want to find the most related or most relevant to your work and include that as background in your presentation. Be sure to include any work that would impact how you interpret your findings.