IB question past paper

Hey guys! Hope everyone is doing well! Can someone please explain these two to me ?

In the first question, I didn’t choose A as NADPH won’t be synthesized from cyclic phosphorylation. I don’t understand how the accumulation of NADP can cause cyclic phosphorylation to occur :disappointed_relieved:

Also in the second question, why isn’t AaBb correct answer ? I thought as they are further apart independent assortment will be just like Mendel’s characteristics

Thanks you so much in advance :ok_woman:t2:🫶🏻


Hi this was a tough one!! I believe the first one is actually not in our syllabus.

However I found that regulation of cyclic photophosphorylation can occur at the level of ferredoxin and is governed by the NADPH/NADP ratio. So higher ratio would cause it to occur.

And I’m not completely sure about Q34 either. It should be possible as when genes are far apart, crossing over happens often enough that all types of gametes are produced with 25% frequency so hmmmm, interesting


Hey Raya! Thank you very much for kindly explaining :heart_eyes_cat::heart:. I thought the same with you for question no 2, may be it’s an error or smth :((.

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Yea probably! Sorry it took so long I just wanted to wait to see if someone else had a better explanation since mine is pretty brief :))

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Oh no, It’s okay! I am really glad that you and other classmates always helped me out whenever I didn’t know something​:ok_woman:t2::two_hearts:. I really appreciate your help every time​:two_hearts:! You are very kind :smiling_face_with_three_hearts:

I think something is wrong with emoji system :joy:


These are really good questions, but I also think Q12 is a little out of the scope for the IMAT. Thanks Raya for explaining it though!

I think I have figured out the answer to Q34. Esentially, the trick is in rotating the sister chromatids (those lines next to each other) vertically instead of horizontally. This makes it clearer that if recombination will 100% occur, as stated by the question (“genes far enough for recombination to occur”), then they very likely mean that NEW genotypes will be created.

Here is my illustration which shows the recombination happening at the green spot. Of course, recombination can also occur between red chromatid “ab” and black chromatid “ab”, which would allow AaBb genotype to remain, so the question is a little weird.


Hey Darius! Thank you so much for the thorough explanation, rotating the diagram helps me visualize the question better ! Thanks a lot :heart:

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Thank you so much Darius, yeah this is a way better technique:))