Edexcel A2 Biology Unit 4(6BIO4) 13/06/11 - OFFICIAL THREAD !

What sort of 'synoptic' topics or material are you guys looking at for this unit? If any at all? At the moment i've looked at everything on the spec but nothing else, as in specifics from AS. Any ideas or recommendations for the synoptic topics they might throw in? .

Anything is fair game.

hi, can some one link me to the specimen?

Macrophages engulf the pathogens and then display the foreign (or non-self) antigens on their surface. When any cell in the human body displays foreign antigens in this way it is known as an antigen-presenting cell (APC).

Macrophages are part of the non-specific and specific immune response. They are non-specific in that when they come across any foreign antigen pathogen they try and engulf and digest them off. They don't know what type of organism they are digesting (i.e. they can't say ooo this is Virus 'X', bad!! - kill it!). They say.. hey.. I don't know if you are Virus X or Y but I do know you're not meant to be part of the body let me kill you.

Then once they present the antigens, this activates the specific immune response (T-cells and B-cells etc. etc.), which have complementary receptors that are specific to that antigen and bind to the antigens via these receptors.

I've put my notes on the immune system response in the spoiler



NOTE: Phagocyte ^ is a general term for any WBC which engulfs and digests stuff. A macrophage is a type of phagocyte.

Antibodies kill a pathogen in many ways:

1) reduce the pathogens' ability to infect cells (don't ask me how coz book doesn't say so and I doubt we need to know)

2) bind to the foreign antigens to make an antigen-antibody complex - which is readily digested by macrophages

3) antigen-antibody complex causes pathogens to clump together preventing them spreading to other parts of the body (don't ask me how again )

When electrons get excited by light in PSII, they leave the chlorophyll but where do they go?

Some places say they are used to form reduced NADP but other places say they go to PSI.
And then electrons excited in PSI go and reduce NADP.

Thank you so much InIt..... : )

One question:
So, does this mean that in the NON-SPECIFIC / INNATE Immune response, B cells produce antibodies which bind to antigens as labels, for enhanced binding to receptors on macrophages? In that case, are the receptors on macrophages specific?

In the Edexcel Unit 4 Biology June 2010 paper, Q4, it states that antibodies and B-cells are involved in the NON-SPECIFIC response. I thought antibodies and B-cells are only part of the SPECIFIC immune response.

Could you please shed some light on this matter? THANK YOU SO MUCH! : )

The electron goes into PS1 TO replace the ones that keep leaving to make reduced NADP

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That's what I thought, but some sources such as Khan academy and the specimen paper (Q1b i), state that the electrons lost from PSII go and reduce NADP.

Please any1 have the past paper and mark schem for the JAN 2011? AND ALSO MARK SCHEME FOR JUNE10 AND JAN10

wELL i THINK THEY ARE PREPARED TO FAIL, if they keep getting mixed up, it states clearly on the diagram and in words thats the electron that leave ps2 is picked ur by the electron transport chain and makes ATP in the process and they electron goes into PS1. I think the must have gotten it wrong somewherre, you are right dont let some sources make you fail.

attached every paper for unit 4. Sorry don't have a pdf version of june 10 ms but you can dload/view it from the link below.

june 10 ms: http://www.scribd.com/doc/46124422/biology-jun-2010-mark-scheme-unit-4



ok thanks. I'm just going to stick with my notes.

E- from psii --> psi
e- from psi --> nadp + (h+) --> nadph
e- from photolysis --> psii

thanks man much appreciated