VCE Biology Question Thread

[katiesaliba]

Which class of MHC markers are b cells activated by?

[sparked]

In the secondary antibody response, why does the antibody level remain high for a long period of time after the infection has cleared , in contrast with the primary antibody response in which the antibody level decreases after the infection has cleared?

This is simply a result of having more B memory cells, meaning that it takes longer for them all to deplete.

I mean, it might also be a product of the body's capacity to recognise that subsequent infections reflect the antigen is present in the environment as a consistent threat... But I don't know if that's the case.

You would very rarely be asked to justify this in an exam though. Just know the graph that indicates heightened response and longer term immunity.

[grannysmith]

Which class of MHC markers are b cells activated by?

extracellular antigens i think

[RazzMeTazz]

Also, are mast cells classified as granulocytes?

[Reus]

Soon to have the SAC -written- (Chromosomes stained blue using orcein ethanoic stain) and almost ALWAYS hypothesis, independent and dependent variable questions are asked haha.
So I know the temperature is a control. However I'm having trouble with a suitable hypothesis.

How's this?
It is hypothesised that if 10mm fragments of garlic roots are incubated, stained and observed then stages of mitosis (interphase, prophase, metaphase, anaphase, telophase) will be evident. 

No idea what the independent and dependent variables include. Any of you guys know?

Thanks. 

[grannysmith]

What effect does interleukin-2 (released by T helper cells) have on cytotoxic T cells? Does it stimulate naive killer T cells to recognise antigens that are specific to their T cell receptors? Then these killer T cells are activated upon binding to specific antigen-MHC complexes of infected/cancerous cells, facilitated by CD8 receptors. They release perforin which punctures and lyses the infected cell.

[RazzMeTazz]

Do B lymphocytes also play a role in organ transplant rejection?

And also how are cytotoxic T cells destroy these transplanted cells, if they usually become activated by binding with MHC marker-antigen complexes on the surface of infected cells.

Wouldn't these transplanted cells only have MHC markers on their surface, not antigens (as they have not been infected with any pathogen themself) ?

[nhmn0301]

What effect does interleukin-2 (released by T helper cells) have on cytotoxic T cells? Does it stimulate naive killer T cells to recognise antigens that are specific to their T cell receptors? Then these killer T cells are activated upon binding to specific antigen-MHC complexes of infected/cancerous cells, facilitated by CD8 receptors. They release perforin which punctures and lyses the infected cell.

Sounds right to me ! Although if you look through exam questions, information about CD4 or CD8 is not highly examinable (but it's kind of fun to know).

Do B lymphocytes also play a role in organ transplant rejection?

And also how are cytotoxic T cells destroy these transplanted cells, if they usually become activated by binding with MHC marker-antigen complexes on the surface of infected cells.

Wouldn't these transplanted cells only have MHC markers on their surface, not antigens (as they have not been infected with any pathogen themself) ?

Correct me if I'm wrong here:
If cytotoxic T cell is activated by the whole process of cell-mediated immunity, then B cell is activated as well, since when helper T cell is stimulated (as mention above by grannysmith), it releases interleukin-2, which plays a vital role in both humoral + cell mediated immunity, then yes, B cell will be activated. (You can see the example of Rhesus incompatibility)
All cells have MHC markers in the surface (except Red blood cells). MHC (major histocompatiblity  complex) alone themselves are not markers, but are GENES that code for marker. Since these genes contain the genetic information of a person, everybody MHC is unique. Hence, when the body see the different coding genes on the transplant tissues, it will recognize them as non-self.
Antigen doesn't always mean non-self molecules, it helps you to differentiate between self and non-self molecules. Hence, in the body, we can have self antigen and non-self antigen, where self can be the glycoprotein producing from the person own cell surface or non-self as the membrane structures, viral protein coats or foreign particles.

[grannysmith]

How does HIV lead to AIDS?
So the HIV infects certain immune cells such as helper T cells and macrophages, which are crucial to a properly functioning immune system. Without helper T cells, humoral and cell mediated responses would not function effectively, as naive B cells and cytotoxic T cells require activation by interleukin-2, which is released by helper T cells. Without macrophages, less pathogens would be destroyed via phagocytosis. Hence, this eventually leads to immunodeficiency.
Is this sufficient?

[RazzMeTazz]

Why are antibiotics ineffective against viruses?

[grannysmith]

Why are antibiotics ineffective against viruses?

Antibiotics generally damage cell membranes, interfere with metabolism or affect cell walls, all of which are not found in viruses.

[grannysmith]

Are epitopes and antigen fragments the same thing?

Also, how do I explain the delay in the adaptive immune response and why it is slower than the innate response?

My answer: the adaptive response is antigen-specific, and thus specific lymphocytes must bind to an antigen in order to elicit a response. It takes time for a lymphocyte to find and bind to its specific antigen, leading to a delay. The innate response is faster as it is non specific and hence a specific leukocyte isn't required.

This seems verbose and not accurate enough. Can anyone help?

[RazzMeTazz]

Can disinfectants and antiseptics kill viruses?


Or is it only antiviral drugs which can kill viruses?

[RazzMeTazz]

Can phagocytes detect non-self antigens on the surface of pathogens and foreign substances?

Is this what causes them to engulf foreign pathogens in the innate immune response?

[grannysmith]

Can phagocytes detect non-self antigens on the surface of pathogens and foreign substances?

Is this what causes them to engulf foreign pathogens in the innate immune response?

Yep, things like macrophages and neutrophils.