VCE Biology Question Thread

[Nomi16]

Can you please tell us which specific ones to know? I have no idea what to memorise for this.

Know the major extinctions they are given in the book. One of them is about the dinosaurs.
Probably have an idea about the background extinction because that section has examples of major extinctions. 

[PhoenixxFire]

When you say naive T cell do you mean cytotoxic T cell or helper T cell?

[zenith101]

When you say naive T cell do you mean cytotoxic T cell or helper T cell?

I believe naive refers to both cytotoxic and helper T cells- just before they have been activated by cytokines/ bound to antigens.

[zenith101]

Are we required to know details about fever and blood clotting?

[PhoenixxFire]

I believe naive refers to both cytotoxic and helper T cells- just before they have been activated by cytokines/ bound to antigens.

Yes I know, I meant which type of cell he was talking about in his answer.

Are we required to know details about fever and blood clotting?

No, this is not on the study design so it cannot be assessed.

[smamsmo22]

When you say naive T cell do you mean cytotoxic T cell or helper T cell?

I mean naive cell in terms of an undifferentiated T cell that could potentially become a Tc or Th cell - that is activated to do so? Is that what you're asking? May have interpreted your question wrong..

[PhoenixxFire]

I mean naive cell in terms of an undifferentiated T cell that could potentially become a Tc or Th cell - that is activated to do so? Is that what you're asking? May have interpreted your question wrong..

Naive T cells have already differentiated into Th cells and Tc cells (this happens during maturation in the thymus). Naive Th cells stay in lymph nodes waiting to bind their antigen and naive Tc cells travel throughout the body attempting to bind to antigens presented on MHC1.

[smamsmo22]

Naive T cells have already differentiated into Th cells and Tc cells (this happens during maturation in the thymus). Naive Th cells stay in lymph nodes waiting to bind their antigen and naive Tc cells travel throughout the body attempting to bind to antigens presented on MHC1.

I think that's where I got myself confused. So naive Tc cells can be activated by binding to specific MCH1 markers of cells infected by a particular pathogen, regardless of the activity of Th cells corresponding to the particular pathogen/antigen (i.e., Tc cells don't have to be stimulated by Th cells to act on an infected cell). Do activated/effector Tc cells proliferate as Tc cells only, and activated Th cells proliferate as Th cells and also differentiate into memory T cells? Or are memory T cells produced from the clonal expansion of both naive Tc and Th cells?

[simrat99]

Hi, can someone please answer the following questions I was having trouble with,
1. When our body receives a pathogenic antigen from a vaccine, is it ingested by a phagocyte and then presented to Th and B cells, or are these cells just activated by recognizing the antigen, without APCs?
2.With an allergic immune response, how are B cells activated? Do they require APCs or Th cells at all?
Thank you

[PhoenixxFire]

I think that's where I got myself confused. So naive Tc cells can be activated by binding to specific MCH1 markers of cells infected by a particular pathogen, regardless of the activity of Th cells corresponding to the particular pathogen/antigen (i.e., Tc cells don't have to be stimulated by Th cells to act on an infected cell). Do activated/effector Tc cells proliferate as Tc cells only, and activated Th cells proliferate as Th cells and also differentiate into memory T cells? Or are memory T cells produced from the clonal expansion of both naive Tc and Th cells?

When a virus infects a cell, both Th and Tc cells are activated. (viral fragments will inevitably end up throughout the body, where APC's find them and present them to Th cells) Tc cells can be activated without a Th cell secreting cytokines (they just have to bind their antigen) but they will not divide and differentiate without the cytokines being release from an activated Th cell.

Th cells will differentiate into activated Th cells and memory Th cells
Tc cells will differentiate into activated Tc cells and memory Tc cells

[PhoenixxFire]

1. When our body receives a pathogenic antigen from a vaccine, is it ingested by a phagocyte and then presented to Th and B cells, or are these cells just activated by recognizing the antigen, without APCs?

Th cells are activated by an pathogen being engulfed and its antigens presented on a MHC 2 molecule by an Antigen Presenting Cell (APC) ie. a macrophage or dendritic cell.
B cells are activated by free antigens - those just floating throughout the body, not presented on MHC2

Th cells cannot recognise antigens that are not presented on MHC2 and B cells cannot recognise antigens presented on MHC2.

2.With an allergic immune response, how are B cells activated? Do they require APCs or Th cells at all?

Initially it is like a normal immune response. This is called sensitisation. As a result of this IgE antibodies against the allergen are produced. These IgE antibodies bind to mast cells, when the allergen enters the body again it binds to these antibodies, causing the mast cells to degranulate (release histamine). This is the allergic response.

[grannysmith]

2.With an allergic immune response, how are B cells activated? Do they require APCs or Th cells at all?

IgE production by B cells requires a Th interaction, and Th proliferation depends on an APC interaction.

[ezferns]

Also Ezferns i'm figuring that out myself (lots of scribbling on paper its hard to find all the information I want in one source) Once i've got it all organised i'll upload it for everyone (probably tomorrow).

Thankyou!!

When talking about organ rejection, is it incorrect to talk about both the action of Tc cells and B plasma cells? I did q5b VCAA 2008 E1 and it only mentioned the cell mediated response in the answer.

[PhoenixxFire]

Thankyou!!

When talking about organ rejection, is it incorrect to talk about both the action of Tc cells and B plasma cells? I did q5b VCAA 2008 E1 and it only mentioned the cell mediated response in the answer.

Generally I wouldn't talk about him humoral immunity when talking about cells unless they mention it. (You can talk about cytokines release by Th cells though).

[LifeisaConstantStruggle]

Thankyou!!

When talking about organ rejection, is it incorrect to talk about both the action of Tc cells and B plasma cells? I did q5b VCAA 2008 E1 and it only mentioned the cell mediated response in the answer.

Just a tiny addition to what has been mentioned above, and a bit of a dig in Wikipedia to confirm my statement (sorry), the humoral response does occur during organ/transplant rejection. So it is technically not incorrect if you talk about the cell-mediated immune response alongside the humoral response. However, the real detrimental effects of organ rejection typically lies on the fact that the cells undergo apoptosis, so I guess, the more important part (involving cell death) of organ rejection is the activity of Tc cells.