VCE Biology Question Thread

[1729]

MHC (Major histocompatibility complex) restriction refers to the fact that cytotoxic t-cells (aka killer t cells) can only activate aganist an antigen that is imbedded in an mhc complex. A cytotoxic T cell cannot respond to an antigen that is not imbedded in an MHC complex.The cell-mediated response is the technical term for the action the cytotoxic-t cells have in the immune response.
Regarding plasmids, plasmids replicate independently of the bacterial chromosome, so they could either be present in their clones in high numbers or not at all depending on whether or not the plasmid was replicated.

Also, MHC restriction is the characteristic of T lymphocytes that they recognize a foreign antigen only when it is bound to a particular allelic form of an MHC molecule (e.g., CD8+ T lymphocyte recognizing the MHC class I HLA-A02:101:01:02N allele but not the MHC class I HLA-A2.2Y0205 allele)

[Chocolatepistachio]

For this question would my answer be right
Explain how each of the following contributes to the movement of water from roots to leaves a) tension in the xylem
B) evaporation of water from the leaf
C) forces of attraction between cellulose fibres and water

A) the tension in the xylem pushes the water up the stem and allows the water to move upwards from the roots to the xylem.- causes water molecules to be attracted to one another
B)  the evaporation of water from the leaf creates a negative pressure in the surrounding cells of the leaf and causes more water to be pulled in to the xylem
C) the forces of attraction between the cellulose fibres and water allows for the adhesion of water to the cell walls of the xylem vessels and allows the water to be held in the stem and leaf when transpiration stops.

[Coolgalbornin03Lo]

MHC (Major histocompatibility complex) restriction refers to the fact that cytotoxic t-cells (aka killer t cells) can only activate aganist an antigen that is imbedded in an mhc complex. A cytotoxic T cell cannot respond to an antigen that is not imbedded in an MHC complex.

[cut rest of quote]

Ohhh so is that why for clinal stimulation of Naive T cells it is the APC presenting that antigen on MHC I marker instead of the free floating antigens which make naive B cells under VO clonal selection.

[1729]

Ohhh so is that why for clinal stimulation of Naive T cells it is the APC presenting that antigen on MHC I marker instead of the free floating antigens which make naive B cells under VO clonal selection.

Yes, pretty much. MHC restriction has been hypothesized to be involved in positive selection of T lymphocytes when considering clonal expansion because the requirement for MHC-associated antigen presentation for T cell activation accounts for the MHC restriction of T cell–B cell interactions. Note that both class I and II MHCs are involved in that model (you only referenced class I MHC above). CD8 and CD4 interact with class I and class II MHC molecules, respectively, and are responsible for the class I or class II MHC restriction of these classes of T cells.

[-Lilac-]

(Note: Some of this is well beyond VCE knowledge)

To add on, MHC restriction really refers to the concept that in the thymus, T cells are positively selected so they can interact with at least one of the MHC alleles expressed by that individual as T cells recognize both parts of the antigenic peptide and the MHC molecule itself. All the other T cells that cannot interact with MHC die.

MHC restriction has some important implications in transplants. 

CD8 and CD4 interact with class I and class II MHC molecules, respectively, and are responsible for the class I or class II MHC restriction of these classes of T cells.

At a stage of development, the thymocytes are what we call 'double-positive' as they will express both CD8 and CD4. During, positive selection they will interact with either self MHC I or MHC II and downregulate either CD4 or CD8 respectively.

Ohhh so is that why for clinal stimulation of Naive T cells it is the APC presenting that antigen on MHC I marker instead of the free floating antigens which make naive B cells under VO clonal selection.

B cells can recognize 'native' antigen. It can be free-floating but sometimes it is bound on the surface of some special cells in the B cell follicle.

T cells on the other hand recognize a combination of self MHC and a processed peptide fragment. In short, T cells can only 'see' antigen when it has been presented to them on MHC. Thus, if you were just to expose the T cells to 'free antigen' they would not clonally expand.

Yes, pretty much. MHC restriction has been hypothesized to be involved in positive selection of T lymphocytes when considering clonal expansion because the requirement for MHC-associated antigen presentation for T cell activation accounts for the MHC restriction of T cell–B cell interactions.

I am not quite sure what you mean by this (I am a little tired so forgive me!) But yes, any B and T cell interaction is MHC restricted as the B cell acts as an APC and presents antigen on MHC to T cells to 'get help.'

[ErnieTheBirdi]

What are good ways to remember all the different hominins and the different homo genus species? What would be some things to look out for in Unit 4?

[Chocolatepistachio]

For this question would this be a sufficient answer
Briefly describe how the kidney regulates salt and water balance
- The kidney maintains a correct balance of salts in the blood by excreting excess salts, this helps to maintain the PH of the blood. The kidney excretes toxic nitrogenous waste such as urea and creatine which forms as a waste product of muscle activity. The osmotic pressure of the blood is also regulated maintaining the optimum balance between water and dissolved salts. The kidneys can conserve water by producing concentrated urine or they get rid of excess water by producing dilute urine.

[1729]

For this question would this be a sufficient answer
Briefly describe how the kidney regulates salt and water balance
- The kidney maintains a correct balance of salts in the blood by excreting excess salts, this helps to maintain the PH of the blood. The kidney excretes toxic nitrogenous waste such as urea and creatine which forms as a waste product of muscle activity. The osmotic pressure of the blood is also regulated maintaining the optimum balance between water and dissolved salts. The kidneys can conserve water by producing concentrated urine or they get rid of excess water by producing dilute urine.

Looks good to me. However, excreting salts doesn't particularly manatin pH, excreting H+ does. Also, remember, it's not accurate to refer to h+ as a salt, because it is an ion. I think you should make that clear. You might also include the RAAS system, which helps maintain optimal blood pressure.

[homeworkisapotato]

What are good ways to remember all the different hominins and the different homo genus species? What would be some things to look out for in Unit 4?

Hey! You definitely don't need to remember every single one. The ones you NEED to know are:
Australopithecus Afarensis
Homo Neanderthalensis (neanderthals)
Denisovans
Homo sapiens (lol)
Handy ones to know are:
Homo Habilis (the ones who started to use tools)
Homo ergaster and erectus (lots of debate who left Africa)

[Chocolatepistachio]

If an organism like Cyanobacteria does not contain chloroplasts how does it perform photosynthesis

[1729]

If an organism like Cyanobacteria does not contain chloroplasts how does it perform photosynthesis

So interestingly, Cyanobacteria has chlorophyll in their cytoplasm, which allows for the light reactions to occur in photosynthesis. Typically in plants, the chloroplasts contain the chlorophyll, but in cyanobacteria (and other what are called blue green algae for that matter) can perform photosynthesis simply from it being present in the cytoplasm.

[homeworkisapotato]

If an organism like Cyanobacteria does not contain chloroplasts how does it perform photosynthesis

They carried out oxygenic photosynthesis, and had chlorophyll stored in their cytoplasm. They used water as an electron donor and produced oxygen, instead of carbon dioxide

Edit: 1729 bet me ahahahaha

[Chocolatepistachio]

Thanks
Also I was having trouble with this question
Explain why the contents of the food vacuole do not digest the body of the paramecium cell

[homeworkisapotato]

It might just be my brain combusting but can you please reword it as I don't understand what the question is asking?

[Owlbird83]

Thanks
Also I was having trouble with this question
Explain why the contents of the food vacuole do not digest the body of the paramecium cell

I think it's looking for an answer about how the contents of the vacuole is separated and from the rest of the cell because it's enclosed by a plasma membrane, preventing digestive enzymes from leaking out into the cytoplasm of the cell.