It's clear you're familiar with the content; I think something for you to work on will be writing concisely to the marking scheme as (especially for the first part of your answer for 6) you sometimes waste time writing uneccessary information.
For 2, you've only given 2 points: that voluntary participation was breached (1) and that this is because the students did not have a choice (1). If you can't think of an additional point for voluntary participation maybe consider a different ethical principle and see if you have find 2 additional points related to that
For 3, you understand the idea but the wording in the 3rd sentence is a little off. Unstandardised procedure is a good starting point, but "discrepancies" is too general (we would expect the two datasets to have some differences even if using a standardised procedure) and might not lead the examiner to give you the 3rd mark - what type of variable would be introduced?
For 6, the original design was repeated measures (not independent groups) so participant variables were already minimised; if you want to swap to repeated measures you'll need to find a different advantage.
Your second part of the explanation uses phrases likely to be in the examiners report and connects them well - very easy to give marks too
For any questions I haven't commented on, I'd give you full marks
It's also clear that you have the background knowledge for answering these questions. Something I would suggest for you to work on is "certainty" in some of your statements - as depending on the examiner/question this could lose you marks. Eg. using "would" when "could" might be more appropriate
Your answers tended to be similar to whys so much of the same feedback applies, especially in regards to q2 & q6
For q1, it would be great to refer to sympathetic nervous system dominance to explain why the threat induces this response
For question 7 you need a unit - eg. pupil diameter (mm)
Hope you've both found this useful - you've both showed a strong start & I hope you only build from here
Let me know if you have any questions, and definitely feel free to post again with fine-tuned answers