VCE Biology Question Thread

[Sine]

Thank you so much! 

1. do we need stabilising, directional and disruptive selection?
2. do we need monoclonal and polyclonal antibodies in depth?
3. do we need to know fungi and parasite lifecycles etc?

thanks

1. yup but I've never seen a question on it XD
All this is for continuous variation
 stabilising: favours middle phenotype
 directional: favours a single extreme phenotype
 distributive: both extreme phenotypical values are favoured
2. No
3. yup just know the terminology as per Biology24123

[vox nihili]

Alright I'm a tad confused. I heard that once an mhc class 2 marker attaches to a helper T cell it releases interlukin 2 which stimulates specific B cells. However I also heard that the helper T cell brings the antigen to B cells and they attach to antibodies on the B cells surface and that's what stimulates them. Can any one explain this to me!?

The 2nd explanation is correct

Other way around. The first one is kind of correct, but too narrow, the second is correct.

T-helper cells are stimulated by antigen presented in MHC class II molecules. They are then able to bind to B-cells and stimulate them. T-hellper cells help B-cells do their thang and also help them proliferate, although don't forget that B-cells also need to bind an antigen separately to be activated too.

Your thing about interleukin-2 (IL-2) is kind of correct. In reality, when a T-helper cells binds a T-cell, it can produce any number of cytokines that stimulate the B-cell. One such cytokine is indeed IL-2, though there are many others.

[cosine]

Other way around. The first one is kind of correct, but too narrow, the second is correct.

T-helper cells are stimulated by antigen presented in MHC class II molecules. They are then able to bind to B-cells and stimulate them. T-hellper cells help B-cells do their thang and also help them proliferate, although don't forget that B-cells also need to bind an antigen separately to be activated too.

Your thing about interleukin-2 (IL-2) is kind of correct. In reality, when a T-helper cells binds a T-cell, it can produce any number of cytokines that stimulate the B-cell. One such cytokine is indeed IL-2, though there are many others.

When all this MHC II - Antibody - TCR complex occurs, do we need to know what chemicals are released and cause the proliferation and activation?

[vox nihili]

When all this MHC II - Antibody - TCR complex occurs, do we need to know what chemicals are released and cause the proliferation and activation?

Nope. That special torture is reserved for university.

[TerryCruze]

Hey guys I have one more SAC this year for Bio, and there was this question in one of the in class practice sacs about why babies were a particular weight in terms of ethics? I had no idea what to write can anyone help me?

[Acid]

How important is it to have a very close understanding of the geological time scale? Is knowing the different eras' general knowledge sufficient or should I be aware of each period and its specifics?

Thanks!

[grindr]

Could someone please help me with this signal transduction question.

The answer is C, I thought the better answer would be D.
Why not? 

[cosine]

Could someone please help me with this signal transduction question.

The answer is C, I thought the better answer would be D.
Why not? 

It's not D because when the gibberelin binds to it's specific transmembrane protein receptor, this is known as detection, and signal transduction only occurs after the detection of the stimulus/signal.

[cosine]

Need some help on this one, I know the semi-conservative theory of DNA replication, but I dont get what the question is asking?

[grannysmith]

Need some help on this one, I know the semi-conservative theory of DNA replication, but I dont get what the question is asking?

So first cycle, DNA unwinds and is replicated using the radioactive nucleotides. This produces two DNA molecules, both of which are composed of an original strand and one new strand. Subsequent cycle, 4 DNA molecules: 2 contain original + new; the other 2 contain new+ new.

[cosine]

So first cycle, DNA unwinds and is replicated using the radioactive nucleotides. This produces two DNA molecules, both of which are composed of an original strand and one new strand. Subsequent cycle, 4 DNA molecules: 2 contain original + new; the other 2 contain new+ new.

Thanks, I did not even read the 'nucleotides' part, thought the DNA strand was originally radioactive.. xD

Define genetic drift:
"Genetic drift refers to the loss of alleles in the gene pool of a population due to non-selective events"
The answer from the assessors report is attached. They say change in allele frequency, but is not genetic drift actually the loss of alleles due to random events? For example, is the founder effect occurs, the original population has indeed experienced a change in allele frequency, but more specifically a loss of alleles? Same with bottleneck effect, this results in the loss of alleles. So would my answer (above) attain full marks? (its out of 1 mark) But does Bio get half marks on the exam?

Thanks in advance

[grannysmith]

Thanks, I did not even read the 'nucleotides' part, thought the DNA strand was originally radioactive.. xD

Define genetic drift:
"Genetic drift refers to the loss of alleles in the gene pool of a population due to non-selective events"
The answer from the assessors report is attached. They say change in allele frequency, but is not genetic drift actually the loss of alleles due to random events? For example, is the founder effect occurs, the original population has indeed experienced a change in allele frequency, but more specifically a loss of alleles? Same with bottleneck effect, this results in the loss of alleles. So would my answer (above) attain full marks? (its out of 1 mark) But does Bio get half marks on the exam?

Thanks in advance

Sorry, no half marks in Bio! Unless of course, one examiner gives you 1 and the other 0, then you'd get 0.5.

Anyway, with any type of genetic drift, we're generally concerned with allele frequency as this can imply a loss of alleles. This is because genetic drift does not necessarily mean a loss of alleles, although this can be the case. Founder/bottleneck effect are special cases of genetic drift which usually involve the loss of alleles.

I always defined genetic drift as: a change in the allele frequency of a population due to random events.

[Sine]

Thanks, I did not even read the 'nucleotides' part, thought the DNA strand was originally radioactive.. xD

Define genetic drift:
"Genetic drift refers to the loss of alleles in the gene pool of a population due to non-selective events"
The answer from the assessors report is attached. They say change in allele frequency, but is not genetic drift actually the loss of alleles due to random events? For example, is the founder effect occurs, the original population has indeed experienced a change in allele frequency, but more specifically a loss of alleles? Same with bottleneck effect, this results in the loss of alleles. So would my answer (above) attain full marks? (its out of 1 mark) But does Bio get half marks on the exam?

Thanks in advance

No half marks in biology but you can obtain them if one exam gives you 1/1 and the other 0/1.

I would give you 0/1marks for that response, genetic drift doesn't actually have to be the loss of alleles its just the change of allele frequencies. Your probably confused as the two examples of genetic drift we explore in VCE Biology are the bottleneck effect and the founder effect which both don't necessarily result in the lost of alleles but usually do.

For instance the founder effect isn't specifically a loss of alleles, although this may occur, its when a group is isolated from a population and they are not representative of the original population. So the actual allele frequencies are changed but alleles don't have to be lost.
Look at the picture on the right.

https://en.wikipedia.org/wiki/File:Founder_effect.svg

EDIT: Beaten by grannysmith

[cosine]

Sorry, no half marks in Bio! Unless of course, one examiner gives you 1 and the other 0, then you'd get 0.5.

Anyway, with any type of genetic drift, we're generally concerned with allele frequency as this can imply a loss of alleles. This is because genetic drift does not necessarily mean a loss of alleles, although this can be the case. Founder/bottleneck effect are special cases of genetic drift which usually involve the loss of alleles.

I always defined genetic drift as: a change in the allele frequency of a population due to random events.

So genetic drift is the change in the allele frequency due to random events, then what is gene flow? Is that change in allele frequency due to migration?

Also can you give me an example of genetic drift where the allele frequency is changed, but is not decreased?

So would my original answer have gotten 1 mark for the explanation?

Thanks

[grannysmith]

So genetic drift is the change in the allele frequency due to random events, then what is gene flow? Is that change in allele frequency due to migration?

Yes

Also can you give me an example of genetic drift where the allele frequency is changed, but is not decreased?

Not sure what you mean by this. Allele frequency is, overall, out of 1. A certain allele may increase/decrease in its frequency.

So would my original answer have gotten 1 mark for the explanation?

It's not entirely incorrect, but examiners may take a mark off.