I love coffee and biology. That’s why I thought I could use my Matura project to investigate exactly how caffeine works in the human body. To do this, I could start by investigating the effect caffeine has on micro-organisms such as paramecia. Under what circumstances, with what intention, and with what respect for life itself, is it permissible to conduct research on micro-organisms? What do I need to bear in mind?
How exactly caffeine affects the human body is a good topic for a Matura thesis. I would recommend that you stick to this question and not switch to paramecia simply because they are easier to work with in the laboratory.
Of course, you will observe an effect of caffeine on the behaviour of paramecia. And there is also a lethal dose, which you can then calculate. But that tells you nothing about the human body. That is why the experiment with paramecia is of no use to your research question.
From an ethical point of view, research on these organisms becomes problematic if you assume that paramecia are sentient beings in any way. However, if, in addition to an in-depth literature review on the effects of caffeine in the human body, you also wanted to carry out some experimental work yourself, you could, for example, measure certain blood parameters in relation to coffee consumption. You could also carry out in vitro experiments with human cells, for example with HeLa cells. These are tumour cell cultures that are available for purchase. But first, you would need to define which parameters you wish to measure.