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A-Level OCR A Biology: Biollogical Membranes Question.

I was doing some questions from physicsandmathstutor in preparation for my mocks and came across this question:
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mark scheme:
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I don't really understand where in the question it hinted to the yeast cells using active transport. Why would the yeast cells use ATP just to allow an indicator to move into the cell? I've only started doing practice questions for AS Level Biology, and it's really disheartening opening up the mark scheme and seeing it says 'IGNORE' many things in my answer.

Thanks!

(I've only started AS Level Biology 2 months ago and the wording of the questions really throws me off. The questions are often misleading, and its sometimes very hard to realise what its asking for. If anyone has tips to getting better at exam technique and writing better answers, except for practice questions as I've already started doing those, please drop them below :smile:

)

(edited 3 years ago)

Reply 1

HarisMalik98

Bit of a whacky question, but here goes...

So first of all, the solution is stated as alkaline; so with only the indicator present it should be yellow.

When the cells become separated from the alkaline solution by centrifugation, they are observed as red/pink (acidic) and the solution is observed as colourless. This indicates that all of the indicator has been transported into the cells, since the solution would be yellow (or pale yellow) if there was residual indicator present, since it's alkaline.

If the process wasn't active, the indicator would only diffuse into the cell until the concentrations inside and out the cell (across the membrane) are equal - i.e. there would still be indicator present in the solution as well as in the cells. This would mean that the cells would be red/pink and the solution would be yellow after centrifuging.

Since no indicator is present in the solution (colourless), that indicates the cells have transported all of the indicator in against the concentration gradient - hence, active transport.

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As for developing better exam technique, you could watch all the youtube videos you want. But really the best way to get better is by doing past papers then marking them. It doesn't matter if you aren't getting 100% straight away, you've just started the course. It's a good thing to learn from your mistakes early on, so you don't make them in the final exams. As you do more papers, you train yourself to understand what certain questions are asking for and the key pieces of information examiners are looking for.

(edited 3 years ago)

A-Level OCR A Biology: Biollogical Membranes Question.

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