VCE Biology Question Thread

[shivaji]

In the allergic response, what actually causes the production of IgE antibodies? these are the steps i have, can somebody please check them??

• organism is exposed to the allergen for the first time
• results in the production of IgE antibodies which travel in the blood stream and bind to mast cell
• mast cells are primed
• second encounter with the allergen produces IgE antibodies which bind to mast cells
• results in the release of histamine, resulting in an allergic response

in the second encounter, IgE antibodies are already bound to mast cells - it is the allergen which binds to these specific IgE antibodies, forming cross-links and resulting in the degranulation of histamine by mast cells.

[Rishi97]

Does anyone have a simple definition for natural selection that can be used for exams?

[millie96]

can somebody please explain the process of macrophages and displaying MHC1 markers?

To get it clear, do MHC1 represent non-self? and MHC2 self with damage

[sandrag]

When describing the existence of variation within a specific population and the effects of natural selection within this population is it more accurate to state that phenotypic variation exists or that genetic variation exists? Any help would be greatly appreciated 

[Vicbelgaus]

When describing the existence of variation within a specific population and the effects of natural selection within this population is it more accurate to state that phenotypic variation exists or that genetic variation exists? Any help would be greatly appreciated 

Here is my two cents worth

I think its more important to state that their is Phenotypic variation. This is because natural selection acts on the phenotype of organisms, with some organisms being better adapted to deal with the selective agents.

Hope that helps, correct me if i'm wrong.

[grannysmith]

In the allergic response, what actually causes the production of IgE antibodies? these are the steps i have, can somebody please check them??

• organism is exposed to the allergen for the first time
• results in the production of IgE antibodies which travel in the blood stream and bind to mast cell
• mast cells are primed
• second encounter with the allergen produces IgE antibodies which bind to mast cells
• results in the release of histamine, resulting in an allergic response

So a B cell with specific antibodies binds to the allergen; clones into memory cells and plasma cells. These plasma cells produce antibodies specific to the allergen, some of which will be IgE. It is these IgE that attach to mast cells.

Does anyone have a simple definition for natural selection that can be used for exams?

Hmm.. The differential reproduction of certain phenotypes due to a selecting agent. Not too sure..

can somebody please explain the process of macrophages and displaying MHC1 markers?

To get it clear, do MHC1 represent non-self? and MHC2 self with damage

So MHC I is found on all nucleated cells, while MHC II is found on APCs.

Say a muscle cell is infected with a virus. It'll display the viral antigens on its MHC I marker. In that way, a cytotoxic T cell with specific receptors to the viral antigen can then bind to the MHC I of the muscle cell.

However, the Tc still needs to be activated by an appropriate T helper cell. Chances are, an APC (macrophage, dendritic cell, or B cell) has recognised a circulating virus with the same viral antigens and has engulfed it. It is broken down, and the viral antigens are then displayed on the MHC II marker of the APC.

Now, Th can only recognise foreign antigens on an MHC II marker. Using its specific receptor, it'll bind to the antigen-MHC II complex on the APC.    Now that an appropriate Th has been activated, it can release chemicals (interleukins) which stimulate that initial cytotoxic T cell into proliferating and differentiating into effector cells and memory cells.
These effector cells can then bind to any MHC I marker displaying that original viral antigen, and release perforins which lyse the virus-infected cell's membrane and induce it to undergo apoptosis.

Wow that was a mouthful.

When describing the existence of variation within a specific population and the effects of natural selection within this population is it more accurate to state that phenotypic variation exists or that genetic variation exists? Any help would be greatly appreciated 

Well, I guess natural selection acts of phenotypes. However, many of the practice exams I've come cross only mention "variation", in addition explaining what that variation is.

Not entirely sure though

[katiesaliba]

1) Do we need to know the differences of transcription and translation in eukaroytes and prokaryotes?
2) What are transcription factors? Do we need to know their function?
3) Do we need to know gene conservation? I've noticed its no longer on the study design anymore
4) To create transgenic organisms, does the inserted DNA have to come from a different species? Or can it just be any foreign DNA
5) Does the genome include ALL genetic material including RNA?

Thanks!

1) I'm fairly certain that we don't need to know about prokaryotic transcription and translation.
2) No. Google image search 'transcription factors' to see what they are if you're curious.
3) It's not in my textbook (N.O.B) or on the study design, so I'm going to assume not.
4) From a different species.
5) Genome is the full set of genes within an individual, so I don't think that includes RNA (unless we're talking about retroviruses, or RNA viruses).

In the allergic response, what actually causes the production of IgE antibodies? these are the steps i have, can somebody please check them??

• organism is exposed to the allergen for the first time
• results in the production of IgE antibodies which travel in the blood stream and bind to mast cell

• mast cells are primed
• second encounter with the allergen produces IgE antibodies which bind to mast cells
• results in the release of histamine, resulting in an allergic respons[/s]e

-organism is exposed to the allergen for the first time
-results in the production of IgE antibodies which travel in the blood stream and bind to mast cell
-Upon re-exposure, the allergenic fragments will cross-link between the IgE antibodies on the mast cells, resulting in the degranulation of the mast cells (histamine released)
-Symptoms of an allergic response thus ensue.
-The immune response increases in significance with each exposure to the allergen, as more antibodies will be produced (by plasma B-cells) against the antigen.

can somebody please explain the process of macrophages and displaying MHC1 markers?

To get it clear, do MHC1 represent non-self? and MHC2 self with damage

-Macrophage encounters a non-self antigen expressed on a pathogen/agent/substance, engulfing it. 
-The engulfed substance travels in a vesicle within the macrophage and fuses with a lysosome, where it is broken down into fragments.
-One of these peptide fragments then complexes with an MHC II and is expressed on the plasma membrane of the macrophage.
-Macrophages are APCs, therefore they possess MHC II molecules for the sole purpose of signalling the adaptive immune response upon foreign invasion.

Every nucleated cell (therefore not RBCs) expresses MHC I. Consequently, MHC I are 'self' detectors. As all MHC receptors have the capacity to express peptide fragments, infected cells will have foreign proteins complexed with their MHC I receptors. Normal cells will possess 'self' peptides complexed with their MHC I molecules. This establishes the differentiation between 'self' and 'non-self'

Therefore, MHC I does express 'self', HOWEVER upon infection (say by a virus) the molecules will express obscure peptide fragments which indicates to the immune system that the cell is not healthy. Then, NK cells (antigen non-specific) or Tc cells (antigen specific) will destroy the affected cells.

I hope that makes sense

When describing the existence of variation within a specific population and the effects of natural selection within this population is it more accurate to state that phenotypic variation exists or that genetic variation exists? Any help would be greatly appreciated 

Phenotypic variation, as natural selection works for/against phenotypes rather than discrete genotypes (because hetero/homo dom will express the same phenotype

[howlingwisdom]

When describing the existence of variation within a specific population and the effects of natural selection within this population is it more accurate to state that phenotypic variation exists or that genetic variation exists? Any help would be greatly appreciated 

Hmmm we were taught to say that there was pre-existing genetic variation in a population (when talking about natural selection or allopatric speciation)?

[katiesaliba]

Hmmm we were taught to say that there was pre-existing genetic variation in a population (when talking about natural selection or allopatric speciation)?

Perhaps something like 'pre-existing genetic variation-resulting in phenotypic variation-existed within the population' would suffice then? 





What's the difference between autoantibodies and antibodies? When explaining autoimmune disease, would I have to mention autoantibodies (from the 2013 assessment report)? I just don't feel comfortable referring to something I don't understand ahaha 

[grannysmith]

Perhaps something like 'pre-existing genetic variation-resulting in phenotypic variation-existed within the population' would suffice then? 





What's the difference between autoantibodies and antibodies? When explaining autoimmune disease, would I have to mention autoantibodies (from the 2013 assessment report)? I just don't feel comfortable referring to something I don't understand ahaha 

Autoantibodies act against self molecules. You probably wouldn't have to mention autoantibodies specifically (although it is better), but as long as you explain that the specific antibodies act against self material, then I'd say it's okay.

[shivaji]

Can antibodies attack cells? Because in autoimmune disorders and alike, autoantibodies are produced which attach self-cells such as myelin etc...
If they do, then what's the point of Tc cells?

[howlingwisdom]

Can antibodies attack cells? Because in autoimmune disorders and alike, autoantibodies are produced which attach self-cells such as myelin etc...
If they do, then what's the point of Tc cells?

Tc cells are more specific in their action; as they only act upon virus infected cells, cancerous cells, transplanted cells and fungi infected cells etc.

[katiesaliba]

For the attached question:
-would it be sufficient to define a phenotype as 'the observable characteristics which are coded for by genes and influenced by the environment'? Because one's biochemistry cannot really be observed per se :')

Would by answer for Bii be accurate:
The genes are still present within the somatic cells and are thus still transcribed and translated.

This is from the 2002 VCAA exam 2.

[grannysmith]

For the attached question:
-would it be sufficient to define a phenotype as 'the observable characteristics which are coded for by genes and influenced by the environment'? Because one's biochemistry cannot really be observed per se :')

Would by answer for Bii be accurate:
The genes are still present within the somatic cells and are thus still transcribed and translated.

This is from the 2002 VCAA exam 2.

I guess the phenotype isn't only what can be macroscopically(?) observable. We talk about different blood types as different phenotypes.

I'd probably mention that ALL the genes are still present and none are lost.

[katiesaliba]

I guess the phenotype isn't only what can be macroscopically(?) observable. We talk about different blood types as different phenotypes.

I'd probably mention that ALL the genes are still present and none are lost.

But would it be correct to state that transcription and translation can still occur as the genes are still present? I don't really understand why it wouldn't be, because the question says that the translocation did not result in abnormalities. And considering chromosomes have telomeres at their ends, gene 'overlapping' wouldn't occur??

For question dii in the attached image, why would the answer be 1/3 and not 2/3? I understand that a 9/18 and a 9 chromosome express a normal phenotype, but why wouldn't a sole 9/18 chromosome also express a normal phenotype-all the genes are still present? Thanks!