VCE Biology Question Thread

[cosine]

Uhh, isn't the diploid number 14? The answer says its 7

Note: It doesn't let me attach the screenshot of the question - it says "Your attachment has failed security checks and cannot be uploaded. Please consult the forum administrator." Basically, its question 4c of the 2011 VCAA exam 2

The male has only three chromosomes, but with their homologous pair it is six. So before meiosis, the sister chromatids will form on each chromosome. During meiosis I, the homologues are separated into differing cells. Then again in Meiosis II, the sister chromatids will again separate, hence each gamete of the male will contain 3 chromosomes.

The female has four chromosomes, with homologues it is 8 in total. So again during Meiosis I, the homologues line up and are separated into differing cells, then during meiosis II, the sister chromatids will separate again and so each egg cell has four chromosomes.

Upon fertilisation and formation of the zygote, the sperm, with three chromosomes, fuses with the egg cell, with four chromosomes, thus the zygote will end up with a diploid number of seven chromosomes, but is probably infertile as the chromosomes are not present in homologous pairs.

[BakedDwarf]

The male has only three chromosomes, but with their homologous pair it is six. So before meiosis, the sister chromatids will form on each chromosome. During meiosis I, the homologues are separated into differing cells. Then again in Meiosis II, the sister chromatids will again separate, hence each gamete of the male will contain 3 chromosomes.

The female has four chromosomes, with homologues it is 8 in total. So again during Meiosis I, the homologues line up and are separated into differing cells, then during meiosis II, the sister chromatids will separate again and so each egg cell has four chromosomes.

Upon fertilisation and formation of the zygote, the sperm, with three chromosomes, fuses with the egg cell, with four chromosomes, thus the zygote will end up with a diploid number of seven chromosomes, but is probably infertile as the chromosomes are not present in homologous pairs.

omg i just realised how stupid i am. I somehow thought that DNA replication also doubles the amount of chromosomes, when i KNOW that it doesn't.

Anyways, thanks for the clear and thorough explanation

[vox nihili]

Do you suggest just going over specific topics that are re-occurring problems by reviewing material notes? I have flash cards per topic made throughout the year so perhaps going over those would help me? Cheers for the response, appreciate it!

It depends on whether those problems have to do with content. To me it seems more or less that you've got a pretty good grip on the content, you're just struggling with details. When revising content, make sure you take down a list of the tiny details you're forgetting and immediately get clarification on stuff that you're not sure about.

Alright so here is my understanding:

RNA polymerase binds to the promoter regions of the template DNA strand. (Still unclear here, so the promoter regions on the DNA are not within the gene, so the promoter region is outside the parameter of the start codon? If so, when the pre-mRNA is spliced, does this promoter region get spliced off? Or if what I said is false, would that mean the promoter region just promotes the RNA polymerase but does not actually get transcripted onto the mRNA?) Once this has occurred, the RNA polymerase moves along the DNA template strand in the 3'-5' direction, simultaneously synthesising the single stranded pre-mRNA molecule, as ribonucleotides are added by the ongoing polymerase to the progressing mRNA strand. As this happens, the mRNA strand peels off and is extending as it is being synthesised. The DNA helix is also being winded back together as the mRNA is being synthesised.

Your second point about promoters is correct. A promoter is a sequence to which RNA polymerase binds that is upstream of the gene (fancy way of saying before the gene). The promoter itself is typically not transcribed. Transcription starts at an initiation sequence upstream (i.e. before) the start codon. Start and stop codons are entirely irrelevant in transcription, they only come into play in translation. Obviously, your point about splicing is irrelevant—the promoter isn't part of the pre-mRNA.



The rest of your explanation about transcription, however, is an absolute work of art.

[Gromekk]

Quick question

a question on a practice exam i got from the teacher asked what is a genome?

I wrote down The genome is the complete set of DNA found in an organism, but the answers say it is only the dna in one chromosome, what is right? It is a qats 2014 one btw

[vox nihili]

Quick question

a question on a practice exam i got from the teacher asked what is a genome?

I wrote down The genome is the complete set of DNA found in an organism, but the answers say it is only the dna in one chromosome, what is right? It is a qats 2014 one btw

Complete set of DNA.

The answer they gave makes me sad inside.

[grindr]

I don't understand these answers, could someone please help?

16) The answer is A. I thought it was D, how do you know that an alternative pathway would always be used, are we to assume this?

SA) I don't get how maternal antibodies would interfere with the foal's immune system.

[heids]

I don't understand these answers, could someone please help?

16) The answer is A. I thought it was D, how do you know that an alternative pathway would always be used, are we to assume this?

SA) I don't get how maternal antibodies would interfere with the foal's immune system.

1.  If this is a commercial exam, it's probably a dodgy answer.  Having written some myself, you often get this cool idea (e.g. let's check if people can think of alternative pathways! yay that'll be great ), but the question finally ends up a bit ridiculous because you have to either 9/10 tell the answer in the stem, or require something that the stem doesn't say.  Ignore this, therefore.

2.  Well, the point of the vaccination was to stimulate the foal to produce their own antibodies (and thus memory cells), right?  But if the foal already has antibodies (from the mother) that react with the attenuated virus, then the foal won't need to make their own antibodies and thus memory cells.  So, no memory cells produced --> poor response in future.

[grindr]

1.  If this is a commercial exam, it's probably a dodgy answer.  Having written some myself, you often get this cool idea (e.g. let's check if people can think of alternative pathways! yay that'll be great ), but the question finally ends up a bit ridiculous because you have to either 9/10 tell the answer in the stem, or require something that the stem doesn't say.  Ignore this, therefore.

2.  Well, the point of the vaccination was to stimulate the foal to produce their own antibodies (and thus memory cells), right?  But if the foal already has antibodies (from the mother) that react with the attenuated virus, then the foal won't need to make their own antibodies and thus memory cells.  So, no memory cells produced --> poor response in future.

Right! That makes sense, thank you!!! 

[vox nihili]

I don't understand these answers, could someone please help?

16) The answer is A. I thought it was D, how do you know that an alternative pathway would always be used, are we to assume this?

SA) I don't get how maternal antibodies would interfere with the foal's immune system.

Yeah it's making some silly assumptions really. But normally if there is an essential molecule a couple of pathways will converge on it, but not always.

[cosine]

This question has been on my mind since I did immunity in term 2.. When we receive a vaccine, the virus is attenuated, so the viral genome is removed right? And because the antigens are still present, an immune response will be conducted but no infection will occur. Then do our normal macrophages and other lymphocytes actually work to kill these viruses when they are detected? For example the virus has lead to B cell proliferation into plasma cells and memory B cells, so it has been effective. But do the plasma B cells now produce antibodies to neutralise/agglutinate the virus?

If the person has never encountered this virus before, does it make a difference if the virus stays in their body for 1 hour or 10 hours? Will the immune response still be the same? Like for example, if the virus stays in the body for longer, would the proliferated memory B cells act upon the antigens when they are detected?

[vox nihili]

This question has been on my mind since I did immunity in term 2.. When we receive a vaccine, the virus is attenuated, so the viral genome is removed right? And because the antigens are still present, an immune response will be conducted but no infection will occur. Then do our normal macrophages and other lymphocytes actually work to kill these viruses when they are detected? For example the virus has lead to B cell proliferation into plasma cells and memory B cells, so it has been effective. But do the plasma B cells now produce antibodies to neutralise/agglutinate the virus?

If the person has never encountered this virus before, does it make a difference if the virus stays in their body for 1 hour or 10 hours? Will the immune response still be the same? Like for example, if the virus stays in the body for longer, would the proliferated memory B cells act upon the antigens when they are detected?

That's the basic idea of it. It mirrors an infection and gives the B-cells an opportunity to expand up and kill off that infection. It's not dangerous though, because the virus has lost the capacity to replicate.

An attenuated virus isn't necessarily one that has lost its genome though. Indeed, the genome quite often stays. You attenuate the virus by removing its capacity to cause serious infections.

In the case of the polio vaccine, the virus is actually alive and able to reproduce. It just can't get into the nervous system and sticks around in the GIT instead. The virus is still infectious too (i.e. it can be passed on) so even if people haven't been vaccinated directly they can pick it up from others.

[cosine]

That's the basic idea of it. It mirrors an infection and gives the B-cells an opportunity to expand up and kill off that infection. It's not dangerous though, because the virus has lost the capacity to replicate.

An attenuated virus isn't necessarily one that has lost its genome though. Indeed, the genome quite often stays. You attenuate the virus by removing its capacity to cause serious infections.

In the case of the polio vaccine, the virus is actually alive and able to reproduce. It just can't get into the nervous system and sticks around in the GIT instead. The virus is still infectious too (i.e. it can be passed on) so even if people haven't been vaccinated directly they can pick it up from others.

If a question asks a way to make an effective vaccine, would saying the removal of the viral genome be correct?
So attenuated and removing genome are different things? Never knew this, though attenuated meant that the genome was removed.

Attenuated =weakened = hard time entering cells as they require host cells to reproduce?

[vox nihili]

If a question asks a way to make an effective vaccine, would saying the removal of the viral genome be correct?
So attenuated and removing genome are different things? Never knew this, though attenuated meant that the genome was removed.

Attenuated =weakened = hard time entering cells as they require host cells to reproduce?

Hmmmmm removing the genome would probably do it, certainly for VCE.
Attenuated just means that the virus has lost its ability to be a pain in the arse essentially. Generally they've been mutated so that they can't get into cells and cause issues.

[Biology24123]

Do we need to know fibrous and globular proteins

[Bruzzix]

Do we need to know fibrous and globular proteins

I don't think it's specifically listed in the study design but it doesn't hurt to know.