VCE Biology Question Thread

[juntyhee]

1. Protein based hormones have longer amino acid chains than peptide-based hormones. You don't need to distinguish between them for VCE though, you just need to know that some hormones are amino-acid based (amine, peptide, protein) and some are steroid based.

2. Not really sure on this. I think it just means that after blebs have been phagocytosed the individual components are reused in the body. Not sure whether they would be broken down into base components or entire organelles reused or what though.

3.
According to VCAA 2016So I'd take this to mean that VCAA believes 'signal for macrophages' is the last step.

4. Haven't got a clue. Definitely not something you need to know for VCE though.

5. Prominent heelbones refers to your heel sticking out. Like if you point your toes you have a bump where your heel is. The selection advantage is that they make bipedalism more efficient and does a better job of supporting the increased weight associated with bipedalism & evolution.

6. Clonal selection is when a B or T cell is activated. Clonal expansion is when it multiplies producing lots and lots of identical daughter cells.

7. Vasodilation does decrease blood pressure but there'll be more blood in the area at any one time because the capillaries are bigger (also it makes it more permeable, which allows white blood cells to cross the membrane as peter.g15 said)


Purely speculation, but given the importance of enzymes I'd imagine that a mutation that resulted in an enzyme functioning less efficiently would probably result in the death of that individual. So in a way yes it would be natural selection. Probably not something you'll ever have to talk about for VCE though haha

Thanks so much!!

[PhoenixxFire]

Would the following be a valid answer for this question?
-Different receptors/second messengers in the two cells leading to different signal transduction pathways
-therefore different genes are activated, producing two distinct proteins

Given the additional information given at the beginning of question 7 and given that part C. refers to the genetic sequence being identical, I would say no.
If the question was more generically referring to how one hormone can cause different responses in different cells then yes your answer would be correct, but in this case it's specifically referring to how one gene can produce more than one protein.

[PopcornTime]

why would it be important to have positive and negative regulators in signalling pathways?
- prevent overreaction by the cell and thus, conserve energy

Thoughts?

[PopcornTime]

Is the following correct?

Physical barriers:
- intact skin
- ear wax

Chemical barriers:
- stomach acid
- lysozyme in tears
- fatty acids on skin

Microbiological barriers:
- natural flora
- expulsion reflexes (sneezing, etc.)
- ciliated lining

[Qwerty1234qwerty]

Can someone please explain to me why not finishing a course of antibiotics contributes to antibiotic resistance?

[peachxmh]

Still a little confused about MHC markers so I wanted to clear something up - are MHC markers only present on human cells or do other pathogens (e.g. virus, bacteria) have MHC markers? Also to summarise the recognition of self-antigens, would it be correct to say that B and T cells, and also APCs recognise the markers (would this only be MHC-I markers?) on cells as self if they have the same markers as themselves? Thank youuuu!

[vox nihili]

Can someone please explain to me why not finishing a course of antibiotics contributes to antibiotic resistance?

Bacteria can be partially resistant to antibiotics, meaning that the antibiotics aren't quite as effective as they would normally be. So if you only use half the course, you only half kill the bacteria, and then the partially resistant bacteria grow back and then constitute the bacteria that get passed around, then they can evolve to become fully resistant.

[darkz]

Is the following correct?

Physical barriers:
- intact skin
- ear wax

Chemical barriers:
- stomach acid
- lysozyme in tears
- fatty acids on skin

Microbiological barriers:
- natural flora
- expulsion reflexes (sneezing, etc.)
- ciliated lining

Yeh looks good 

Still a little confused about MHC markers so I wanted to clear something up - are MHC markers only present on human cells or do other pathogens (e.g. virus, bacteria) have MHC markers? Also to summarise the recognition of self-antigens, would it be correct to say that B and T cells, and also APCs recognise the markers (would this only be MHC-I markers?) on cells as self if they have the same markers as themselves? Thank youuuu!

MHC markers are only present in vertebrates, so no, they would not be present in pathogens. As for the recognition of self markers, I'm pretty sure that most of the immune cells can do this, e.g. if a macrophage comes across a cell with self markers, then its not going to eat it. The same logic here also applies to APCs, T and B cells. As for the MHC markers, MHC Class I markers are used to distinguish between self and non-self, while the MHC Class II markers are for the professional APCs to present the antigen on

[EllingtonFeint]

Could somebody please help me!!
This is my first time ever posting on here and I am so confused about this noe bio question.
So for the 2017 VCAA Bio exam, multiple choice questions 38 and 39 have got me so utterly baffled.
Could somebody please explain them to me. I have no idea what’s happening with these two questions and UGH so confused. Any help would be greatly appreciated

I’ve attached the questions too BTW

Thank youuuuu

[PhoenixxFire]

Could somebody please help me!!
This is my first time ever posting on here and I am so confused about this noe bio question.
So for the 2017 VCAA Bio exam, multiple choice questions 38 and 39 have got me so utterly baffled.
Could somebody please explain them to me. I have no idea what’s happening with these two questions and UGH so confused. Any help would be greatly appreciated

I’ve attached the questions too BTW

Thank youuuuu

Hey, welcome to AN

38. So this question is testing that you know how restriction enzymes and gel electrophoresis works.

So to start with, use row T. Row T only has two DNA fragments. In the answers table we can see that HaeIII, SaII, and BamI are the possible restriction enzymes that could have cut that fragment. Of those 3 restriction enzymes, HaeIII is the only one that has a single cut site drawn on the DNA strand above. This means that it is the only one that could have resulted in two DNA fragments (the rest would have resulted in 3). So now we know that the answer must be A or B

So then we use row U. Only options A or B on the table could have cut the DNA fragment. So it must be either BamH1 or Sall. Looking at the DNA fragment above, we can we that Sall would result in 1 short piece and 2 longer pieces, as seen on the gel electrophoresis in row U whereas Sall would result in two short pieces and one longer piece. Therefore it must have been Sall that cut this DNA fragment (option B). Therefore we now know that the answer is option B (you can also double check that option B also works for rows R and S).

39. I've attached this. Let me know if it doesn't make sense.

Still a little confused about MHC markers so I wanted to clear something up - are MHC markers only present on human cells or do other pathogens (e.g. virus, bacteria) have MHC markers? Also to summarise the recognition of self-antigens, would it be correct to say that B and T cells, and also APCs recognise the markers (would this only be MHC-I markers?) on cells as self if they have the same markers as themselves? Thank youuuu!

MHC markers are only present in vertebrates, so no, they would not be present in pathogens. As for the recognition of self markers, I'm pretty sure that most of the immune cells can do this, e.g. if a macrophage comes across a cell with self markers, then its not going to eat it. The same logic here also applies to APCs, T and B cells. As for the MHC markers, MHC Class I markers are used to distinguish between self and non-self, while the MHC Class II markers are for the professional APCs to present the antigen on

Just wanted to add to this, immune cells don't really detect 'self', self is the absence of non-self (at least for VCE). Also I'm not sure if it's just the way you worded the question or not - It's not MHC that determines if a cell is infected by a pathogen - it's the peptide fragments presented on the MHC. (Although variations in MHC can indicate cancer and can cause tissue rejection in the case of transplants).

Peptide fragments produced within a cell are presented on MHC 1 - if the cell is infected with a virus then the cell will be making foreign peptides. If a Tc cell can bind to this fragment, it means that the fragment is non-self and therefore that the cell is infected.

From discussions on here in the past I'm pretty sure that immune cells can recognise some self markers, but for the purpose of VCE, an immune cell recognises something as self by being unable to bind to the antigen presented (e.g. on MHC1, i.e. the absence of non-self particles)

[galaxy21]

Hi just wondering, with plant hormones, which ones do we need to know about? Do we need to know if they bind to intracellular or extracellular receptors in cells?

[Scribe]

Hi! I have a couple of questions regarding transcription factors.

1) What are transcription factors?
2) Are transcription factors coded for by regulatory genes?
3) Are repressors transcription factors? If not, where do repressors/transcription factors come from?
4) Where do transcription factors bind? Do they bind to the promoter, operator, repressor etc. ?

Thanks!

[galaxy21]

Hi!
Can somebody please explain the difference between gram negative and gram positive bacteria? Do we need to know this for the study design?
Thanks

[darkz]

Hi! I have a couple of questions regarding transcription factors.

1) What are transcription factors?
2) Are transcription factors coded for by regulatory genes?
3) Are repressors transcription factors? If not, where do repressors/transcription factors come from?
4) Where do transcription factors bind? Do they bind to the promoter, operator, repressor etc. ?

Thanks!

Transcription factors are basically regulatory proteins - so the regulation of gene expression e.g. enhancers, silencers, activators, repressors. Therefore yes, they are coded for by regulatory genes. General transcription factors help RNA polymerase to bind to the promoter, hence promoting gene expression, or repressors block RNA polymerase etc. Here's a pretty good article on this from Khan academy https://www.khanacademy.org/science/biology/gene-regulation/gene-regulation-in-eukaryotes/a/eukaryotic-transcription-factors

Hi!
Can somebody please explain the difference between gram negative and gram positive bacteria? Do we need to know this for the study design?
Thanks

Gram staining is to classify whether bacteria have peptidoglycan present in their cell wall or not. Gram positive means that they do have peptidoglycan present, and gram negative means that it is not present. This is useful to know, as bacteria with a certain cell wall composition can be more susceptible to certain antibiotics. And yes, I believe this falls under " the use of scientific knowledge to identify the pathogen" on the study design

[darkz]

Does anyone have some stats or knowledge on the 2017 bio exam? That is, assuming SAC scores are maximised, what exam scores were required for 45/47/50?