@I just finished my bio EE a few weeks ago finding the topic and scientific explanation is the hardest. If these two are good the rest of the EE is going to be quite easier. For the topic you need to think something that can be varied as you will need to have 5 different variables for example you are seeing effect of iron. on plants, you will need to have 5 different concentrations of iron. What I did was out down 10 topics and highlighted the ones I was interested in and gave my biology teacher to choose which is the most suitable. Ofc didn't happen at once we went through almost 50 topics from which most of them were rejected and some were not ethical. Somethign else you have to look into the IB has ethical guidelines due to which I had to abandon an EE topic I actually loved. Try something with vision tests and different background colors when taking the vision tests or how does being on the computer affect vision by taking a visual acuity test. Something in that direction if you are interested.