VCE Biology Question Thread

[Apricot]

NOTE: You may be required to talk about cell mediated immunity depending on the type of vaccine being talked about.

For this bit, if we were asked to outline the immune response to a vaccine but it was for a virus, should we discuss the humoral component only or cell mediated too? This is considering cell mediated will only be activated if the vaccine antigens somehow gain entry into a body cell, e.g attenuated virus.

[sharlenelai]

What is the official ATP yield for the electron transport chain?

[helpmepls112]

Other people have answered most of your questions. Just wanted to clarify that Th cells do not generate B cells. They secrete cytokines which cause already activated (have bound their antigen) B cells to divide and differentiate. Also the activated B cell and Th cell have to interact to cause the Th cell to release cytokines. See my post I quoted above for more on this.

im confused...
If i say antigens presented by APC's are presented to naive Th cells, which now become activated T cells release cytokines which divide and differentiate B cells into b plasma cells and b memory cells.

Is what i just said all wrong? And is it wrong if i don't mention the naive b cells already binding to a free antigen in the humoral response because that whole concept confuses me...help

[Domek]

Hi guys,
Can someone please explain to me the Out-Of-Africa theory, I don't understand. Is it that all homo Erectus left Africa to colonise the world, which then evolved into heidelbergensis which them evolved into Neanderthals and Homo sapiens, all of which died out except Homo sapiens and that the hominids in African eventually evolved into homosapiens too, which is why they have more genetic diversity and no neanderthal DNA??

Out of the Africa model basically says that Homo erectus migrated out of Africa and became distributed all over the world. Populations of Homo erectus became genetically isolated with no gene flow occurring between them and eventually independently evolved into different hominin species. However, Homo sapiens did NOT leave Africa when Homo erectus did. Homo sapiens evolved in Africa and migrated out of Africa a long time after Homo erectus. Homo sapiens then displaced the other hominin species living outside of Africa that were descended from Homo erectus. Evidence that supports this theory includes:
- overall, there is little genetic variation in Homo sapiens, as we evolved from a single common ancestor in Africa
- the highest level of variation in mtDNA in Homo sapiens is found in populations as they have had a longer time to accumulate genetic differences
- the oldest fossil evidence of Homo sapiens is found in Africa

I hope this helps

[PhoenixxFire]

For this bit, if we were asked to outline the immune response to a vaccine but it was for a virus, should we discuss the humoral component only or cell mediated too? This is considering cell mediated will only be activated if the vaccine antigens somehow gain entry into a body cell, e.g attenuated virus.

If the vaccine contains an attenuated virus then it is capable of entering body cells and producing peptide fragments that can be presented on MHC 1. Therefore Tc cells will be activated producing memory Tc cells. I would talk about both, but in less detail than you would with only a cell mediated immunity question. (due to marks allocated)

[PhoenixxFire]

im confused...
If i say antigens presented by APC's are presented to naive Th cells, which now become activated T cells secrete cytokines which proliferate B cells into b plasma cells and b memory cells.

Is what i just said all wrong? And is it wrong if i don't mention the naive b cells already binding to a free antigen in the humoral response because that whole concept confuses me...help

B cells do not proliferate into B plasma and B memory cells they differentiate. Proliferate means one cell dividing into copies of itself (which also happens). The rest of that is correct.
You should mention that a B cell will bind a free antigen, then find an activated Th cell. If they have bound the same antigen the Th cell will release cytokines causing proliferation (many copies being made) and differentiation (B plasma and B memory cells being made). That is all you need to say regarding that.

-A naive B cell will bind to a free antigen (ie. not presented by an APC).
-A Th cell will be presented with its antigen on a MHC2 molecule by an APC.
-The 'selected' B cell and Th cell will then find each other and if they have bound the same antigen, the Th cell will release cytokines.
-These cytokines cause the B cell to divide (proliferate) and differentiate into B memory cells and B plasma cells.
-These cytokines also cause the Th cell to divide (proliferate) and differentiate into Th memory cells and Th active cells.
-The memory cells remain in the body to fight subsequent infection by a pathogen with the same antigen specificity and the B plasma and Th active cells fight off the current infection.

[helpmepls112]

B cells do not proliferate into B plasma and B memory cells they differentiate. Proliferate means one cell dividing into copies of itself (which also happens). The rest of that is correct.
You should mention that a B cell will bind a free antigen, then find an activated Th cell. If they have bound the same antigen the Th cell will release cytokines causing proliferation (many copies being made) and differentiation (B plasma and B memory cells being made). That is all you need to say regarding that.

Okay, THANK YOU SO MUCH!!!

[Seno72]

Hello guys. Is it required if we know what apical dominance (and geotropism and phototropism) is or do we need to know just the basic function of each plant hormones (gibberellins, auxin, cytokinins, ethylene and abscissic acid)?

[PhoenixxFire]

Hello guys. Is it required if we know what apical dominance (and geotropism and phototropism) is or do we need to know just the basic function of each plant hormones (gibberellins, auxin, cytokinins, ethylene and abscissic acid)?

Just the basic function. The rest of it is no longer in this study design.

[TheBigC]

Hello guys. Is it required if we know what apical dominance (and geotropism and phototropism) is or do we need to know just the basic function of each plant hormones (gibberellins, auxin, cytokinins, ethylene and abscissic acid)?

Phototropism and geotropism is not part of the study design... just being aware of the basic plant hormones is enough

[Seno72]

Also, in the first exposure to an allergen, does the immune system release histamine to fight against the allergen or is just only in subsequent exposures?

[omxrk]

Just confused about one thing, after bacteria are transformed with, for example the insulin gene, how are the products (insulin proteins) delivered to patients? Are the recombinant plasmids directly injected into a human or do the bacteria first produce the protein and only the proteins are injected into the human?

[TheBigC]

Also, in the first exposure to an allergen, does the immune system release histamine to fight against the allergen or is just only in subsequent exposures?

Only after sensitisation (so subsequent exposures).

[PhoenixxFire]

Just confused about one thing, after bacteria are transformed with, for example the insulin gene, how are the products (insulin proteins) delivered to patients? Are the recombinant plasmids directly injected into a human or do the bacteria first produce the protein and only the proteins are injected into the human?

The proteins are extracted (we don't need to know how) and used for insulin injections.

[PhoenixxFire]

What is the official ATP yield for the electron transport chain?

32. (so 36 total for aerobic respiration)

You may be able to get away with writing slightly different amounts, however DO NOT write a range (eg 32-36) VCAA will not like it (they see it as taking multiple guesses to the answer - if you forget just pick one).