Edexcel IAL Biology Unit 4 June 2016

My main problem with Unit 4 is the timing. I am fine with the content and all but does anybody have any tips for time management? I mean both Unit 6 and 4 have the same time but one is for 50 marks and the other is for 90 marks. I really don't know how to finish the paper in time. Please help!

I have issues with time aswell! I take atleast 20 minutes extra!

Me too! How are you planning on keeping within the time limit? Is there any tricks for that?

I don't really know but I guess I'll divide time as 10 minutes per question at the begining!

Oh. I guess i'll give that a go. Which topic do you find the most frustrating to answer questions about? Coz Unit 4 theory is simple but its the questions that give you a headache.

Just a bit of trouble with cyclic and non-cyclic phosphorylation, as it isn't in the spec and it's confusing, rest is fine.
eeerrrr except immunity (T-cell and B-cell ****)
Hby?

All of the ecology ****. I understand the theory but answering questions is always confusing. I never get the full marks for that question. i.e if it is a 3 marks question, i get 1 or 2. I just don't know where I am going wrong. How do you feel about Ecology?

Just a bit of trouble with cyclic and non-cyclic phosphorylation, as it isn't in the spec and it's confusing, rest is fine.
eeerrrr except immunity (T-cell and B-cell ****)
Hby?

I am also really struggling with ecology , the questions just seem unfamiliar but I guess with practice, we will get there

All of the ecology ****. I understand the theory but answering questions is always confusing. I never get the full marks for that question. i.e if it is a 3 marks question, i get 1 or 2. I just don't know where I am going wrong. How do you feel about Ecology?

Hey, can you specify what exactly you don't understand in cyclic and non-cyclic phosphorylation, I think I might be able to help somehow!

I kinda get cyclic thing but I don't understand the electron flow in non-cyclic. It'd be sooooo great of you if you could explain me x)

Yeah sure, I am glad to explain but would you mind If I do it tomorrow morning because I am little tired and need to finish the paper I am solving!

Sure, I'd be counting on you x)

Okay, to understand it thouroughly, you have to imagine like a it is happening in front of you, use your imagination....

In non-cyclic phophorylation, both PSI and PSII are involved. It is called non cyclic, because it doesn't involve any cycle, it's just reactions involving PSI and PSII.
1) Dissociation of water occur spontaneously, producing H+ and OH- , When light shines, the electrons in both PSI and PSII get excited. Let's begin with PSI, the electron gains energy and rise to a higher energy level, it is picked by the electron acceptor NADP, at the same time NADP accepts an H+ ion that was produced from the dissociation of water to become reduced NADP and that will be used in the Calvin Cycle late on.

2) The electron excited from PSII, rise as well to higher energy level, it is picked by another electron acceptor (NOT NADP) and then it is passed along the electron transport chain where it loses energy, this energy is used to form ATP from ADP and Pi group. then this electron proceeds to PSI, so PSI has gained the lost electron, however, PSII become unstable due to being in shortage of one electron so what happens is, OH- ions that are produced from the dissociation of water lose 4e to PSII to form O2 and 2H2O, 4OH- + 4e = O2 + 2H2O, this process is know as photolysis. So PSII has gained the lost electron, it is stable once again and the process repeats from there

Hope you have understood!!

Yesssss, thankyou! That was awesome!:bban:

That thing involving cd4, with the binding on the receptors and b cells and t cells and basically the whole of immunity ffs If anyone has any notes for immunity I'd be so grateful! x