VCE Biology Question Thread

[wingdings2791]

Hey everyone,
I just got a trial exam back from school (did it in our own time, marked by teachers) and for this question I only got 1/2:

b. Explain how the sections of the diagram labelled 6, 7 and 8 play an essential role in regulating the expression of the lac operon.
Repressor proteins (6) bind to allolactose ( in the presence of lactose, causing a conformational change to the repressor protein. This causes the repressor to be no longer complementary to the operator region (3), so it cannot bind to it and block RNA polymerase from transcription. This leads to the expression of the lac operon. In the absence of lactose, the repressor proteins are complementary to the operator and block transcription by blocking RNA polymerase from binding to the promoter.

I don't have access to the marking scheme, so it would be great if someone could read over and tell me where I went wrong. Thanks guys!
Btw this is the Insight 2020 trial if that's helpful

[darkz]

Hey everyone,
I just got a trial exam back from school (did it in our own time, marked by teachers) and for this question I only got 1/2:

b. Explain how the sections of the diagram labelled 6, 7 and 8 play an essential role in regulating the expression of the lac operon.
Repressor proteins (6) bind to allolactose ( in the presence of lactose, causing a conformational change to the repressor protein. This causes the repressor to be no longer complementary to the operator region (3), so it cannot bind to it and block RNA polymerase from transcription. This leads to the expression of the lac operon. In the absence of lactose, the repressor proteins are complementary to the operator and block transcription by blocking RNA polymerase from binding to the promoter.

I don't have access to the marking scheme, so it would be great if someone could read over and tell me where I went wrong. Thanks guys!
Btw this is the Insight 2020 trial if that's helpful

Well, personally, your answer does seem solid, but insight generally has a really narrow marking scheme - in this case, you may have simply lost the mark because you didn't specifically reference structure '7' in your answer.

[wingdings2791]

Well, personally, your answer does seem solid, but insight generally has a really narrow marking scheme - in this case, you may have simply lost the mark because you didn't specifically reference structure '7' in your answer.

Thank you!! Also, since it's pretty specific, would you recommend going into that level of detail on the actual exam?

[darkz]

Thank you!! Also, since it's pretty specific, would you recommend going into that level of detail on the actual exam?

Yeh, so if the question asks you about certain structures, you should always try to identify what they are first and then explain their purpose.

[Moonblossom]

Does anyone know if there are vcaa sample exam answers?

[PhoenixxFire]

Does anyone know if there are vcaa sample exam answers?

There isn't any written by VCAA but there's some answers compiled by AN members here

[Coolgalbornin03Lo]

I have no idea why I can’t understand the extremley difficult immunity  on exams. I’m not sure what it is but SPOILER FOR 2019 EXAM

Spoiler

I didn’t understand the “can you make this vaccine” in the thunder dust part of the exam I mean I actually didn’t understand

Also if they asked us allergen vs inflammation response I’d be screwed


I was also wondering since genetic screening was removed should we only know social, bio and ethical implications for gene cloning and gene therapy?

[Coolgalbornin03Lo]

I have no idea why I can’t understand the extremley difficult immunity  on exams. I’m not sure what it is but SPOILER FOR 2019 VCAA EXAM proceed with care!

Spoiler

I didn’t understand the “can you make this vaccine” in the thunder dust part of the exam I mean I actually didn’t understand

Also if they asked us allergen vs inflammation response I’d be screwed


I was also wondering since genetic screening was removed should we only know social, bio and ethical implications for gene cloning and gene therapy?

I have no idea why I can’t understand the extremley difficult immunity  on exams. I’m not sure what it is but SPOILER FOR 2019 EXAM

Spoiler

I didn’t understand the “can you make this vaccine” in the thunder dust part of the exam I mean I actually didn’t understand

Also if they asked us allergen vs inflammation response I’d be screwed


I was also wondering since genetic screening was removed should we only know social, bio and ethical implications for gene cloning and gene therapy?

[miyukiaura]

Hey guys,

In the 2018 nht exam I was unsure about the sample answers:
Q: How can the absolute age of the ancient mollusc fossils be used to estimate the age of the
P. portelli fossil?
A: The age of the fossil molluscs would have been worked out using radiometric potassium–argon or
uranium–lead dating in which percentages of the parent isotope and its breakdown product are
measured. The radiometric dating is done on igneous rock layers associated with the sedimentary
layers in which the fossil molluscs have been found elsewhere in the world.

Is it necessary to specify what kind of rock layer is dated (igneous or sedimentary)? And isn't it easier just to say that the rock layer in which the fossil mollusc is found is analysed (instead of mentioning comparisons with layers in other parts of the world)?

[Bri MT]

You can't do it based on sedimentary rock dating because it's like if you buried something in sand at the beach - different bits of sand will have different ages and they won't match the age of the thing you buried.

[miyukiaura]

So absolute dating is always on igneous rock (or the fossil itself)?

[Coolgalbornin03Lo]

So absolute dating is always on igneous rock (or the fossil itself)?

Carbon dating is specifically on organic matter of fossil.

But Argon-Potassium or rubidium blah blah is on the ROCK which the fossil is in.

Hope that clears it up 

[wingdings2791]

I have no idea why I can’t understand the extremley difficult immunity  on exams. I’m not sure what it is but SPOILER FOR 2019 EXAM

Spoiler

I didn’t understand the “can you make this vaccine” in the thunder dust part of the exam I mean I actually didn’t understand

Also if they asked us allergen vs inflammation response I’d be screwed


I was also wondering since genetic screening was removed should we only know social, bio and ethical implications for gene cloning and gene therapy?

Hey Coolgalbornin03Lo,
I think this question was asking for an understanding that vaccines:
a) Intentionally trigger an immune response that leads to production of memory cells
b) Do this by exposure to specific antigens
So to answer this question, you would need to identify that because allergic responses = unwanted immune responses, vaccines would not work against them because vaccines promote stronger, faster immune responses against antigens instead of reducing them. Also, that since vaccines promote responses against specific antigens, that this wouldn't work for pollen because pollen comes from many different plants (there are a lot of different pollen antigens)
Hope this helps!

[makram]

With question 4c from the 2019 exam, why would the fact that many allergens contribute to an allergic response be relevant here? I say this since flu vaccines incorporate many antigens from different influenza strains, so wouldn't it be possible to make a vaccine that uses many pollen fragments?

Could someone also please explain the exam report's answer to question 10B:
'Scientists could have extracted mitochondrial DNA from the young girl’s finger bone sample but, instead, extracted and sequenced nuclear DNA.
Explain why the scientists chose to sequence the nuclear DNA for this sample.'

 (I know it is off the study design, but it would still be nice to know  )

Spoiler

Mitochondrial DNA is only inherited from the mother (and would therefore provide very similar DNA
samples to other female ancestors); however, nuclear DNA contains the whole genome.

Thank you

[wingdings2791]

With question 4c from the 2019 exam, why would the fact that many allergens contribute to an allergic response be relevant here? I say this since flu vaccines incorporate many antigens from different influenza strains, so wouldn't it be possible to make a vaccine that uses many pollen fragments?

Could someone also please explain the exam report's answer to question 10B:
'Scientists could have extracted mitochondrial DNA from the young girl’s finger bone sample but, instead, extracted and sequenced nuclear DNA.
Explain why the scientists chose to sequence the nuclear DNA for this sample.'

 (I know it is off the study design, but it would still be nice to know  )

Spoiler

Mitochondrial DNA is only inherited from the mother (and would therefore provide very similar DNA
samples to other female ancestors); however, nuclear DNA contains the whole genome.

Thank you

For 4c, the main thing is that the allergic response is unwanted; it doesn't defend the body against damage as the allergen isn't a pathogen (the allergen is wrongly identified as potentially harmful when it's really innocuous). The goal in treating allergic responses is to just get rid of them since they don't do anything for the body apart from produce unnecessary symptoms. Vaccines promote/increase immune responses. So making a vaccine against the pollen would just make the allergic response even greater instead of reducing it.

As for 10b, I think it might be because mtDNA is highly conserved, as stated in the marking scheme (very similar DNA samples to other female ancestors), so there won't be enough differences in mtDNA to make any meaningful inferences about the girl's evolutionary history. Nuclear DNA provides a lot more DNA to work with and also has a much higher degree of variation than mtDNA because of recombination.

Not sure if I've explained it well enough but that's just my take on it