hello, I just wanted to know how do you write an aim? what's included in it?
For the aim just keep it simple:
'To investigate the effects of (input IV here) on (input DV here)'. This may be different depending on the type of study done but one sentence should usually suffice.
how come studies on animals cannot be generalised onto humans? I understand the concept of this but not quite sure how i would answer it
I wouldn't worry too much about that. I don't think you will ever need to answer it in an exam, but I guess because animals have different functioning and structures so there's no evidence to prove it will have the same effects on humans.
Also, the sample can only be generalised to the population, which wouldn't be humans in this case.