They are not wrong but I feel like they rarely are enough for full marks. Sometimes I know what they want and I understand the sample answer is just a guide but for example the fruit flies question I myself wasn't sure at all what they want from me so I was looking forward to looking at the sample answer.. but then I see that.. which I'm extremely confident will not get 3 marks.. Probably 1 mark..
Well if they
are right then they may just be very specific. Remember the marker is only looking for the answer to the question and if you can do that in a word, then they have to give you the mark.
So in the second example, if they are looking for TWO things then they only want TWO things, not three, not four. If you properly EXPLAIN (key words are important to answering the question) the TWO things then I don't think they can downgrade you marks for that.
With your fruitfly example it is an OUTLINE which actually doesn't require much writing. The sample answer TBH seems more appropriate for that question than the second question IMO. They've outlined what he did and observed. So I think that would be 2-3 marks..
But again, I don't do bio, so tbh I'm not sure if the answers are actually right in terms of fully answering the question. E.g. I see "sex linkage" in the question and don't explicitly see those words in the answer, so I'm not sure if they actually addressed the full question or not.. But I'll let you decide that. But the second one, I feel is a bit brief for a four mark question... You may want to delve deeper into explaining cause and effect - especially if you know more content from your bio course for that. But remember, keep it related always to TWO examples, not three or four... I'm not saying provide more examples cuz I don't think that would help you at all. Rather, if you know more about those TWO examples, include more analysis (I would probably go for at least four points, two for each example) on EXPLAINING of those two. E.g. Keep synthesising on HOW "Curling the leaves reduces water loss from the stomates." and it's EFFECT, (e.g. cause and EFFECT). Now this may be just me rambling on cuz I don't know much about HSC bio...
Hope it helps though!