2012 VCAA Biology Unit 3 Suggested Answers

[LOLs99]

for the question about first line of defence, can you talk about skin acting as the first physical barrier against infection as well as mucous membranes?

I bet you can because I wrote those as well but make sure u said intact skin(instead of just "skin").

It will be fine as it specified AT LEAST 3. However, if you mislabelled something you may lose the mark.

Histamines granules and receptor site for igE acceptable for that question?

[InsaneMcFries]

Yeah that should be alright.

[LOLs99]

Yeah that should be alright.

Thank you

[spherelin]

hey guys, i know this has been asked many times, but what do you all think the estimated mark for A and A+ is?

[InsaneMcFries]

A+ 60-61
A 55-56

[missunknown]

A+ 85%
A 75%

[InsaneMcFries]

I really don't think A+ will be 85%. That's like 63 marks.

[Panicmode]

I really don't think A+ will be 85%. That's like 63 marks.

Sounds about right IMO. 62-64 will be A+.

[WhoTookMyUsername]

61-62 IMO

[Sassy12399]

For question 16 MCQ, isn't he answer A because O is a universl donor, however it can't accept other blood types? It can't be option D because blood group AB is known as a universal acceptor, hence agglutination should not occur.
Also, for the negative feedback question, depolarization is a positive feedback mechanism, and the question spoke about  hyperpolarization(opposite of depolarization) where the Na channels close as opposed to opening, preventing an influx of Na ions, hence it would be negative feedback??
It's either that or I'm just one confused kid who over studied.

[Scooby]

For question 16 MCQ, isn't he answer A because O is a universl donor, however it can't accept other blood types? It can't be option D because blood group AB is known as a universal acceptor, hence agglutination should not occur.

The question asked when agglutination would occur if antibodies were added to a sample of the blood. Type O blood has no antigens, so adding anti-A antibodies won't have an effect, so A can't be right. The same would happen with the other samples. Adding anti-B antibodies to type AB blood will cause agglutination, so it has to be D.

[andrewt]

Hey I'm just wondering for question 8(a)(ii) in the short answer section how could 'Y' be oxygen because oxygen isn't a compound.
Please explain

[Scooby]

Hey I'm just wondering for question 8(a)(ii) in the short answer section how could 'Y' be oxygen because oxygen isn't a compound.
Please explain

The answer is oxygen, but VCAA screwed up. They might give a mark to everyone for that question

[Sassy12399]

For question 16 MCQ, isn't he answer A because O is a universl donor, however it can't accept other blood types? It can't be option D because blood group AB is known as a universal acceptor, hence agglutination should not occur.

The question asked when agglutination would occur if antibodies were added to a sample of the blood. Type O blood has no antigens, so adding anti-A antibodies won't have an effect, so A can't be right. The same would happen with the other samples. Adding anti-B antibodies to type AB blood will cause agglutination, so it has to be D.

Ohh ok thank you, you are definitely correct, I should have read the question properly. Do you know the answer to my second question?

[Scooby]

Also, for the negative feedback question, depolarization is a positive feedback mechanism, and the question spoke about  hyperpolarization(opposite of depolarization) where the Na channels close as opposed to opening, preventing an influx of Na ions, hence it would be negative feedback??
It's either that or I'm just one confused kid who over studied.

It's important not to confuse the positive charge of a neuron and a positive feedback system. Depolarisation does result in an influx of Na+ into the neuron, making its membrane potential more positive, and it's what occurs before an action potential is produced. However, it's simply the way an action potential is generated - although the membrane potential is positive, this isn't a positive feedback system. For something to be a positive feedback system, the response to a particular change in a variable has to produce a change in the same direction.

Positive and negative feedback is referring to a response of a network of cells that alters a particular variable in some way. It doesn't refer to the membrane potential of a neuron.