Humoral immunity help A-level biology AQA

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medrejectlol
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#1
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#1
Please could anyone help me understand what I need to know about humoral immunity for AQA A level biology? I've done a past paper and the markscheme doesn't match my understanding and what I've seen on youtube videos.

My understanding (from my notes):
1. Specific B cell binds to the antigen of the pathogen (on pathogen / antigen presenting cell / free antigen)

2. B cell processes the antigens and presents them on its cell-surface membrane

3. B cell is stimulated to divide by helper T cells which release cytokines

4. B cell is activated to divide by mitosis to produce clones of plasma cells, which produce and secrete the specific antibody complementary to the specific antigen (clonal expansion)

5. Some become B plasma cells which secrete large amounts of monoclonal antibody into the blood, (primary immune response)

6. Some become B memory cells which can respond to future infections by the same pathogen by dividing rapidly and developing into plasma cells that produce the specific antibodies, (secondary response)

Mark scheme:
1. Helper T cell/TH cell binds to the antigen (on
the antigen-presenting cell/phagocyte);
2. This helper T/TH cell stimulates a specific B
cell;
3. B cell clones
OR
B cell divides by mitosis;
4. (Forms) plasma cells that release antibodies;

Basically I thought it was B cells that bind to the antigen on the pathogen but the mark scheme says the T helper cell does this.

Any help could be really appreciated thank you!
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Jpw1097
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#2
Report 1 month ago
#2
(Original post by medrejectlol)
Please could anyone help me understand what I need to know about humoral immunity for AQA A level biology? I've done a past paper and the markscheme doesn't match my understanding and what I've seen on youtube videos.

My understanding (from my notes):
1. Specific B cell binds to the antigen of the pathogen (on pathogen / antigen presenting cell / free antigen)

2. B cell processes the antigens and presents them on its cell-surface membrane

3. B cell is stimulated to divide by helper T cells which release cytokines

4. B cell is activated to divide by mitosis to produce clones of plasma cells, which produce and secrete the specific antibody complementary to the specific antigen (clonal expansion)

5. Some become B plasma cells which secrete large amounts of monoclonal antibody into the blood, (primary immune response)

6. Some become B memory cells which can respond to future infections by the same pathogen by dividing rapidly and developing into plasma cells that produce the specific antibodies, (secondary response)

Mark scheme:
1. Helper T cell/TH cell binds to the antigen (on
the antigen-presenting cell/phagocyte);
2. This helper T/TH cell stimulates a specific B
cell;
3. B cell clones
OR
B cell divides by mitosis;
4. (Forms) plasma cells that release antibodies;

Basically I thought it was B cells that bind to the antigen on the pathogen but the mark scheme says the T helper cell does this.

Any help could be really appreciated thank you!
B cells do not bind to antigen that is presented on antigen presenting cells, B cells are actually antigen presenting cells themselves. B cells bind antigen, internalise it and present it on their surface.

T-helper cells bind to this antigen which has been presented on the surface of the B cell. This interaction activates the B cell via both the physical interaction and through cytokines which the T-helper cell secretes.

Your answer is more correct than the MS - that's A level for you!
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medrejectlol
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#3
Report Thread starter 1 month ago
#3
(Original post by Jpw1097)
B cells do not bind to antigen that is presented on antigen presenting cells, B cells are actually antigen presenting cells themselves. B cells bind antigen, internalise it and present it on their surface.

T-helper cells bind to this antigen which has been presented on the surface of the B cell. This interaction activates the B cell via both the physical interaction and through cytokines which the T-helper cell secretes.

Your answer is more correct than the MS - that's A level for you!
That makes much more sense thank you!
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