No, you can put it in there if you feel it adds something to your application. Most likely, it doesn't add anything. I don't think it's even unusual to leave the SAQ blank.
Same rules that apply to the personal statement apply to the SAQ and everything else: show; don't tell.
e.g. Don't say "I really like Chemistry" - because this is both meaningless and doesn't show it at all. (Anyone can write this). Instead write something that proves your passion/interest.
For the SAQ, I really don't see what spelling out your intended modules does. I suppose it means you read the website or some other information and thought for more than a minute about what modules you'd probably want to do. In reality this would probably be assumed by admissions tutors, particularly for a more unique course like NatSci. If the admissions tutors thought about the SAQ for more than a handful of seconds, they'd probably just reflect on that sentence as filler, rather than showing anything special about the applicant.
In my SAQ, I wrote just about parts of chemistry and Biology I found interesting (since my Personal statement was for physics) and about a small project I did in my free time related to them. But I'm pretty sure I never explicitly said "I want to do IA Chemistry".
Something good to put in the SAQ is basically something you have done which demonstrates your interest. e.g. building a home made rocket out of mints and diet coke (talk about the pressure and chemistry specifically though), optimising a paper airplane fold with a lot of iterations (talk about the Bernoulli effect, etc.), running a simple computing evolution simulation with (whatever easily downloadable library), doing the basic matrix math required for 3D models in games and graphics, or for proof of concept of a medical MRI machine. I remember a very stupid thing I did once with a tennis racket, some custard and a bike.
Non practical things are also completely fine, provided you actually know what you're talking about. So a few lines about your favourite chapter in a book, or (a bit more dangerous) talking about current research in a particular field of science (this is dangerous because there's a decent chance your future interviewer could be an expert, so I would heavily advise against giving the impression that you are an expert or even remotely competent in your understanding).