VCE Biology Question Thread

[cosine]

No. Remember that self antigens are not recognised at all. The immune system has no capacity to identify self, it can only identify non-self.

This is not correct. Primase only synthesises RNA primers for DNA replication. RNA polymerases do not need primers.

As an aside: the reason RNA primers are used is because RNA sticks to DNA better than DNA sticks to DNA. Therefore, they don't have a tendency to fall off DNA, as DNA primers would.

Would you say then that the antigens on the tumour cells are not recognised as non-self, as they contain antigens that are similar to that of the devil's cells?

[vox nihili]

So RNA primase synthesises an RNA Primer in which this attaches to its complementary DNA base. And when this happens, only then is DNA polymerase able to synthesise the new DNA strand?

When we state the steps in DNA replication, do we have to state that RNA primase synthesises RNA primers which bind to the 3' end of the single stranded DNA molecules? Or can we just start by saying that primers are attached to the 3' end and .. ?

It'd probably be enough to say that primers attach to 3' end of the template strand. I've never read a question that requires an understanding of primase or mention of primase.

The Bacterium U is recognised as non-self as, on its surface, it has:
A. self antigens
B. MHC Class I markers
C. MHC Class II markers
D. glycopeptidase chains

From what I have learnt about the immune system for the past few days, is that only multicellular organisms possess MHC I markers. MHC II markers would be present on APCs and not bacteriums, so B and C are out. I don't know what D even is, so is the answer A? Assuming they are talking about self antigens, that is, self to the bacterium and nonself to the organism that is infected, right?

Absolutely shit house question. I'd just ignore it if I were you.

The answer is D though.

Would you say then that the antigens on the tumour cells are not recognised as non-self, as they contain antigens that are similar to that of the devil's cells?

The tumour cells are not recognised as foreign because of their similarity to self cells of the devil.

Something along those lines. You could also get away with saying they have self antigens and therefore are not recognised as foreign. For the VCE course, indeed, this second answer would be the better one.

[bananabreadbelle]

General question: To what extent do we have to know/be able to explain action potential in neurons?
 

[vox nihili]

General question: To what extent do we have to know/be able to explain action potential in neurons?
 

You just have to know that it's mediated by sodium and potassium and that the Sodium-potassium pump maintains a concentration gradient.

They've taken a lot of the detail about action potentials off the course, so what you need to know is really, really vague

[StupidProdigy]

'anaerobic conditions are required for successful fossilisation'..why is this? I tried thinking about why oxygen is needed but I couldn't make a connection... thankyou

[vox nihili]

'anaerobic conditions are required for successful fossilisation'..why is this? I tried thinking about why oxygen is needed but I couldn't make a connection... thankyou

Oxygen is quite a strong oxidant, so it degrades biological material. If there's less oxygen around, the rate of decomposition of biological material is much slower.

[cosine]

'anaerobic conditions are required for successful fossilisation'..why is this? I tried thinking about why oxygen is needed but I couldn't make a connection... thankyou

For VCE, its as simple as the presence of oxygen will prevent fossilisation, because the organism remains will be subject to decay, so if the remains decay before they fossilise, then how can they fossilise?


Same goes with water, but I read somewhere that lack of oxygen, but presence of water will still allow fossilisation, can someone confirm this?

EDIT: Beaten by the great

[StupidProdigy]

Thanks guys, always helpful!
I've got another question...(attached)
I didn't find this question that bad but it was the wording "small populations." I thought that genetic drift is best observed in small populations instead of defined by it..thankyou again

[cosine]

Thanks guys, always helpful!
I've got another question...(attached)
I didn't find this question that bad but it was the wording "small populations." I thought that genetic drift is best observed in small populations instead of defined by it..thankyou again

You forgot to attach it

Help with the following please:

14. I got 1/2 chance, is this correct? Answer says that its 2/3 :/

For the second one, I just don't even know where to start. Where can I learn about Primates i struggle a lot ..

[Biology24123]

You forgot to attach it

Help with the following please:

14. I got 1/2 chance, is this correct? Answer says that its 2/3 :/

For the second one, I just don't even know where to start. Where can I learn about Primates i struggle a lot ..

It's 2/3 because you are only counting individuals who have the trait. pp is not included.

As for hominid traits, it's pretty much rote learning. I'd say A but's probably wrong

[cosine]

It's 2/3 because you are only counting individuals who have the trait. pp is not included.

As for hominid traits, it's pretty much rote learning. I'd say A but's probably wrong

Aren't we counting the Pp genotype? o.O

[cosine]

Thanks guys, always helpful!
I've got another question...(attached)
I didn't find this question that bad but it was the wording "small populations." I thought that genetic drift is best observed in small populations instead of defined by it..thankyou again

Observed, defined, same thing xD

You can easily cancel out the rest:
D. Movement of continents is not genetic drift
C. Genetic drift is a result of non-selective pressures, so it cannot be C
B. Genetic drift does not really lead to speciation, in the case of the founder effect, I guess it could because if a population colonises another habitat, then it could speciate, but genetic drift also accounts for bottleneck effect. Bit unsure on this one..

It says 'best described as' so, in A, it says that genetic drift is best described as small changes in allele frequencies within small populations, be it founder or bottleneck effect.

[cosine]

For the attached question, can the answer be divergent evolution? Isn't divergent evolution a process? Ah I suck at evolution..

[Biology24123]

Aren't we counting the Pp genotype? o.O

Ok. So we know that III-3 is unaffected so his genotype can't be pp. Therefore we don't count it.
There are 3 genotypes left and two of them are Pp, therefore 2/3 chance

[Biology24123]

For the attached question, can the answer be divergent evolution? Isn't divergent evolution a process? Ah I suck at evolution..

Seems a bit ambiguous. Allopatric speciation or natural selection?