I despair when I'm asked questions like this as it shows the flaws in the teaching of biology in Scottish schools and FE colleges.
Your teachers/lecturers should have sat you down and given you some guidance on how to choose a topic for the investigation that is of interest to you. It's part of the responsibility of the teacher/lecturer to discourage students from being over-ambitious.
I really think that selecting sleep-deprivation as a topic is fraught with difficulties and I wouldn't recommend it. You would have to organise at least one control group and have a good, basic knowledge of statistics to interpret the data properly. Adhering to the investigation methods you'd decided upon would also be problematical. Most importantly there is a risk of harm involved. Sleep deprivation studies in the UK have to be licensed by the government and carried out in specially equipped facilities.
I know I haven't really answered your question but I think you need to sit down and think about biology topics that interest you. Start at the top by deciding whether botany, zoology or microbiology interest you most and work from there. Alternatively, you may have a greater interest in such things as biochemistry or ecology.
I'd suggest you run your ideas past your teachers or lecturers during term time to see what they suggest, but it may not be essential. When you have a better idea of the topic you'd like to investigate, post here again and I'll see if I can help.