2008 VCAA Sample Exam 1 Solutions

[stonecold]

The two three mark questions on UV-Vis and TLC on VCAA09 were difficult, but you just needed the three main points to get the marks. 

[m@tty]

They were the most weird questions on the paper, I thought. Didn't understand what qualitatively determine purity even meant... I thought it was already assumed impure... Anyway, all you needed was three basic points about what to undertake to run the analysis and then interpret the results.

[physics]

87% D:

[chansthename]

Q20 multiple choice.

Question 20
A piece of double stranded DNA, which is 100 base pairs in length, contains 30 guanine bases.
The number of thymine bases in the piece of DNA will be
A. 20
B. 30
C. 50
D. 70

The answers states that it is D (their reasoning provided in the image attached)

Now my reasoning is as follows:

100 base pairs - 2 strands. 30 G bases, that means that there are another 30 C bases for the G to bond to. therefore we have 60 out of 100 in C-G bonds. the remainder is 40. now there has to be an equal number of A and T. therefore the answer is 20 T bases.

Where have I gone wrong? (or is the 'answers' wrong?) (keeping in mind the answers are 3rd party not VCAA)

[stonecold]

Base PAIRS = 100 x 2 = 200 in total.  You'll get where you went wrong from there.

It is one of the biggest tricks they play.  Interchanging the words double stranded, single stranded, bases and base pairs is a ploy to stuff up many students.

My biggest rule in VCE.......RTFQ (read the f***ing question)...if only I could learn to follow it haha!

[chansthename]

Those b******s,

I see my error now, I never really read the pairs, just skipped in in my mind or something (ready for it now though)

[Slumdawg]

Yer I remember when I first did that base pairs one I was like How on earth am I gonna spot tricks like that all the time. Then I saw that exact same question pop up in like 3 different practice exams.

[Stroodle]

man, I hate having to read questions

[Martoman]

 :2funny: