Why would Edexcel ask a question that's NOT in the textbook/ revision guide/ spec?

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Adorable98
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Like what I don't understand is why would they do that?!!! :mad::mad:

This question came up in June 2014 (R).
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In the markscheme it says:
1. idea that the rate increases when the concentration increases / eq ;
2. this increases the concentration gradient / eq ;
3. idea that {plateau / levelling off} of curve due to channel proteins being saturated with molecules (of the substance) / eq ;
4. idea that no more can be carried (per unit time) / max rate of entry reached /eq ;


What I wrote was that
the rate increases because it's going from a high concentration to a low concentration.
It increases to the point where there's a net movement. The rate on both sides of the membrane is constant.


But the things mentioned in the mark scheme is NOT found or explained in neither of my revision guides nor my textbook!
I even checked the spec and all it says
1.4.4. Explain what is meant by passive transport (diffusion,facilitated diffusion), active transport (including the roleof ATP), endocytosis and exocytosis and describe theinvolvement of carrier and channel proteins in membranetransport.
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RMNDK
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(Original post by Adorable98)

What I wrote was that
the rate increases because it's going from a high concentration to a low concentration.
It increases to the point where there's a net movement. The rate on both sides of the membrane is constant.
The thing is, this is not a graph of how the concentration gradient changes over time.
This is a graph showing the effect of different starting concentration gradients and the rate of uptake.

Say you had 100 carrier proteins and the external concentration of the substrate is 50 (arbitrary unit). You'd have a high rate of uptake.
If you had 100 substrate, you'd have an even higher rate.
If you had 150 substrate, it's not going to go any higher. There's only so many carrier proteins. You can think of the carrier proteins as a limiting factor at this point.

As for the information not being available in your textbook, perhaps its outdated? It's just one of them things you need to learn I guess.
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Adorable98
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(Original post by RMNDK)
The thing is, this is not a graph of how the concentration gradient changes over time.
This is a graph showing the effect of different starting concentration gradients and the rate of uptake.

Say you had 100 carrier proteins and the external concentration of the substrate is 50 (arbitrary unit). You'd have a high rate of uptake.
If you had 100 substrate, you'd have an even higher rate.
If you had 150 substrate, it's not going to go any higher. There's only so many carrier proteins. You can think of the carrier proteins as a limiting factor at this point.

As for the information not being available in your textbook, perhaps its outdated? It's just one of them things you need to learn I guess.
Thanx
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Romanoff
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Are you self-teaching this?

This is a typical data response question (as you have in Edexcel Biology), you have to look at the information presented and describe the data: i.e. saying the rate increases when concentration increases and eventually plateaus because ... now you present some common sense and try explaining/backing up your answer as to why it may happen i.e. you know what facilitated diffusion is (because it is on the spec) - when molecules are transported into the cell through channel/carrier proteins and if it is plateauing then this must obviously mean that the channel protein has reached it's maximum capacity.

Easy 2 marks, make sure you spend a little bit reading the question, understanding which part of the specication it fits in with and then thinking what it might involve.
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