VCE Biology Question Thread

[Shenz0r]

And can you please give me a VCE explanation of how certain phagocytes, such as neutrophils or macrophages actually detect pathogens? I mean, im pretty sure our billions of phagocytes encounter many other cells, but how exactly do they recognise a foreign molecule?

Cheers.

Phagocytes recognise foreign molecules as they will have receptors that recognise structures that are common to foreign things (like the proteins and stuff in a bacterial cell wall, or a virus' nucleic acid etc). It's important to note that they can't specifically recognise what the foreign thing is, just that it's foreign, so they won't be able to say differentiate between different bacteria. They're the PRRs that Travis mentioned earlier but I don't think that detail is required in VCE

Also, how and I emphasise how, how are antigens recognised by phagocytes and other white blood cells involved in the non-specific second line of defence? I have a little understanding but unsure if this is correct. I think that certain receptors on these phagocytes bind with the MHC Class I molecules of the foreign particles and don't recognise them, hence engulfing the whole particle?

Quote wikipedia: The phagocytes move by a method called chemotaxis. When phagocytes come into contact with bacteria, the receptors on the phagocyte's surface will bind to them.

I got told earlier that we should just refer to the phagocytotic receptors as 'receptors', but do these receptors bind to the antigens of the pathogen? Is it simply what was said earlier that these receptors bind with MHC Class I markers of pathogens which display non-self antigens and hence the complex will lead to the engulfing of the pathogen?

I think you're confused about what MHC is. MHC is only recognised by T-cells. They are pretty much a protein that presents peptides from inside the cell to T-cells. Kinda like a rubbish bin of sorts. The crap you see in someone's bin is probably going to tell you about what they're like, whether they seem like the dodgy guy or not, and it's the T-cells that sift through these people's bins and then get activated if they see weird stuff.

VCE Bio is a bit vague, but there are specific receptors. They're not the ones that bind MHC. Basically, some antibodies might cover the pathogen and then the phagocytes will have receptors that bind to the antibody and they use that to help engulf the pathogen. Or the complement system produces a protein that covers them and that also binds to another receptor on the phagocyte, working in a similar way to the antibodies.

[paper-back]

Can a teacher deduct marks for "waffling" even though you've gotten the points across? My teachers keep referring to how examiners will not bother to read your answer if you write too much

[grannysmith]

Can a teacher deduct marks for "waffling" even though you've gotten the points across? My teachers keep referring to how examiners will not bother to read your answer if you write too much

Technically, they shouldn't be taking off marks. If you've expressed your answers clearly, and they're correct, you should be paid the marks regardless of how much writing there is. It only becomes an issue when waffling makes your points incoherent to the examiner.

Either way, they give you a certain number of lines for the answer and you're most certainly entitled to filling it all up

[nhienhien852]

Do we need to know about blood clotting/resolvins this year?

[vox nihili]

Can a teacher deduct marks for "waffling" even though you've gotten the points across? My teachers keep referring to how examiners will not bother to read your answer if you write too much

They can, as ultimately it's up to them how they mark your SACs, but they shouldn't. In some ways it's not a bad idea to use SACs to teach you how to write exams properly, so I daresay you'll make up the marks you've lost by actually doing what they've asked.

Do we need to know about blood clotting/resolvins this year?

Nope.

[chemzy]

Guys do we need to know about spermatogenesis and oocytes etc this year?

[vox nihili]

Guys do we need to know about spermatogenesis and oocytes etc this year?

no.

[cosine]

So a specific question asks: "How would the immune system distinguish self from non-self material". What could you say? If you mention MHC markers, this only talks about the T-cells, but then what about B-cells recognising the foreign specific antigens ?

I know I asked this question before, but I am still unclear because I just found out that only T-Cells interract with MHC Markers, but I also know that B cells have antibodies on their membranes to detect specific antigens. So, how would you answer this question if it were in the exam, because I have a feeling it will be on this year's.

[Reus]

So a specific question asks: "How would the immune system distinguish self from non-self material". What could you say? If you mention MHC markers, this only talks about the T-cells, but then what about B-cells recognising the foreign specific antigens ?

I know I asked this question before, but I am still unclear because I just found out that only T-Cells interract with MHC Markers, but I also know that B cells have antibodies on their membranes to detect specific antigens. So, how would you answer this question if it were in the exam, because I have a feeling it will be on this year's.

All cells with nuclei have MHC 1 markers (so only erythrocytes don't). Additionally B Cells have MHC 2 markers as they are APCs.

That might help to answer your question

[KingDrogba]

Doing past papers and making an exam error book, what ways can i make the most out of this study resource to ensure i dont make the same mistakes? Simply reading over it everyday? Writing out common errors?

Thank you!

[cosine]

Thanks Reus,

So if immune cells detect foreign pathogens through binding with specific non-self antigens presented on their MHC I markers, what is the case with viruses? Do viruses also present their self (non self to us) antigens on MHC I markers? If so, this may be too deep but does this occur during the invasion of the host cell, when they are assembling, the Mhc I are embedded within their membranes?

Also, what about allergens and pollen? Surely they don't have MHC I markers, or do they? Are pollen cells or?

Thank you

[Biology24123]

Thanks Reus,

So if immune cells detect foreign pathogens through binding with specific non-self antigens presented on their MHC I markers, what is the case with viruses? Do viruses also present their self (non self to us) antigens on MHC I markers? If so, this may be too deep but does this occur during the invasion of the host cell, when they are assembling, the Mhc I are embedded within their membranes?

Also, what about allergens and pollen? Surely they don't have MHC I markers, or do they? Are pollen cells or?

Thank you

When a cell is infected, it will show virus antigens on it's MHC I. Bacteria usually do not enter cells, so bacteria antigens would usually not be presented on MHC I. The cell displays antigens on it's own MHC 1, NOT the viruses. Proteins and other molecules are constantly updated on the membrane of the cell. This is how antigens end up on the MHC I

[Biology24123]

Thanks Reus,

So if immune cells detect foreign pathogens through binding with specific non-self antigens presented on their MHC I markers, what is the case with viruses? Do viruses also present their self (non self to us) antigens on MHC I markers? If so, this may be too deep but does this occur during the invasion of the host cell, when they are assembling, the Mhc I are embedded within their membranes?

Also, what about allergens and pollen? Surely they don't have MHC I markers, or do they? Are pollen cells or?

Thank you

Allergens don't enter the cell, they bind to receptors on B cells

[cosine]

When a cell is infected, it will show virus antigens on it's MHC I. Bacteria usually do not enter cells, so bacteria antigens would usually not be presented on MHC I. The cell displays antigens on it's own MHC 1, NOT the viruses. Proteins and other molecules are constantly updated on the membrane of the cell. This is how antigens end up on the MHC I

Don't bacteria produce antigens on their own MHC I markers?

Also, so you are saying that viruses dont actually possess MHC markers, but when they infect the host cell, they present their antigens on that host cell's own MHC I markers?

[Biology24123]

Don't bacteria produce antigens on their own MHC I markers?

Also, so you are saying that viruses dont actually possess MHC markers, but when they infect the host cell, they present their antigens on that host cell's own MHC I markers?

Yes, it's the same for both viruses and bacteria. But bacteria mostly don't infect cells so they are engulfed by APC's and are displayed on MHC II