I just wished to check this- is there a difference between how you write a text response for a Unit 3 SAC compared to a Unit 4 SAC?
'Cos the performance descriptor for the Unit 3 text response says 'Analyse, either orally or in writing, how a selected text constructs meaning, conveys ideas and values, and is open to a range of interpretations'
...whereas the performance descriptor for the Unit 4 text response says 'Develop and justify a detailed interpretation of a selected text'
And if there is a difference between the responses required for each unit, would you write in the Unit 3 or the Unit 4 style for the exam's section 1?
Thanks! 
Short answer: No, the Semester 1 and 2 Text Responses are the same, just on different texts.
Long answer: No, because the Study Design is stupidly written and offers schools a bunch of choices none of them take. Technically speaking, any one of the tasks you do in Semester 1 can be in oral form, as the Design requires 1/4 (that is, a L.A. T.R. Context piece, and persuasive/POV) except every single school I know choses to make the persuasive piece the oral task.
You're also technically allowed to bring in more resources for the Unit 3 text, though most teachers discourage this because they're trying to make the SACs throughout the year as similar as possible to the exam task
unlike some other subjects *coughLiteraturecough*This is kind of bridging into knightrider's question:
When mentioned in criteria or questions what "social, cultural and historical values are evident".
What does this actually mean.
what do they want us to state or expect us to include in our writing.
Every T.R. text is chosen for, amongst other things, its ability to relate to a social or historical context. This might be in the time the text is set (eg.
This Boy's Life, Stasiland) or the time the author is writing (eg.
Cloudstreet, Brooklyn) or both (eg.
Henry IV, White Tiger.) Most texts still support both discussions, so what the assessors are looking for is an awareness of how certain values can be seen or presented in the text. You can look at this from either the author or audience's perspective. Not every argument lends itself to this kind of discussion, and you shouldn't base your entire contention on a wider message, but the socio-historical stuff makes for good 'zoomed out' discussion. It's usually pretty hard to form a proper interpretation of the text without an understanding of what the author is trying to say overall; just don't rely too heavily on it in your essays.
Pro tip: If you're integrating some background information, weave it into a sentence with textual discussion
Rather than: 'The idea of body image is something that has plagued young people throughout modern age.
The Very Hungry Caterpillar critiques the idea that self-worth should be derived solely from one's external appearance.'
Transition more fluidly: '
The Very Hungry Caterpillar critiques the idea that self-worth should be derived solely from one's external appearance, thereby forming part of Carle's commentary on the wealth of body dysmorphic problems in the modern age.'
In that first example, you risk not getting credit for the first sentence because it doesn't relate to the text; you're just commenting on the context. In the second, however; you can almost trick the assessor into seeing the connection just by combining the sentences.
So in terms of the actual
range of interpretations part:
The words
whilst, although, despite, and
whereas are your greatest allies. You're not expected to spend a great deal of time on alternate interpretations, but an easy way of doing it is to say something like:
'Whilst the caterpillar's journey could be viewed as one of blissful ignorance, there is an underlying sense of self-realisation and enlightenment in the text.'
I've just drawn a distinction between my contention (self-realisation is important to the caterpillar's journey) and an alternate interpretation (the caterpillar is blissfully ignorant.)
Words like 'although,' 'whilst' etc. force you to add that extra clause as a way of challenging interpretations, so include them every so often and you should be fine for this category.
Of course, there's every possibility that your teacher will have a totally different 'interpretation' of the criteria

so check with them in case there are any bizarre requirements they want you to fulfill.