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GCSE biology triple science help (AQA)

Hi, i have my exam next week as you may know. i was doing some past paper questions and i was doing fine until i stumbled across one question about pregnancy tests and monoclonal antibodies.

i know how monoclonal antibodies work in a pregnancy question however this question is weird and i think it was a 6 mark question in a biology aqa paper a few years ago.

https://www.elevise.co.uk/g-a-b-h-p1-s1-q11-a.html

^ that is the link with the question on it. the question specifically i don't understand is 11.3, stating:

The pregnancy test strip will show a positive test result when a woman is pregnant.
Explain how the pregnancy test strip works to show a positive result. [6 marks]

the mark scheme is underneath as well.
it's not very clear on the stages in the mark scheme, so i am quite confused which hormone goes to where.

i'd appreciate it if you could perhaps explain the mark scheme answer in a more easier and approachable format? (dumb it down for all i care, i'm just trying to understand!)

thank you :smile:
basically...
monoclonal antibodies are just a large amount of lymphocytes for a certain pathogen. the antibodies are put on the stick. (tell me if you don't know how those antibodies are created)
when someone is pregnant, their pee has a hormone in it (you don't need to know why for gcse but just that it has a hormone) which is related to the pregnancy. the hormone is like a (good) pathogen (in terms of lymphocytes/pathogen relationship). when a pregnant person pees on the stick, the hormones will eventually come in contact with the monoclonal antibodies, releasing a dye (the lymphocytes see the 'pathogen' and bind to it).
obviously, a control is needed for the test to make sure that the test is working

i learnt this topic a while ago but i hope i wrote everything correctly and it made sense haha
here are some videos as well that you should probably watch
https://www.youtube.com/watch?v=umRe7GBJ5GE
https://www.youtube.com/watch?v=aOfWTscU8YM
Original post by harlz_chalamet
Hi, i have my exam next week as you may know. i was doing some past paper questions and i was doing fine until i stumbled across one question about pregnancy tests and monoclonal antibodies.

i know how monoclonal antibodies work in a pregnancy question however this question is weird and i think it was a 6 mark question in a biology aqa paper a few years ago.

https://www.elevise.co.uk/g-a-b-h-p1-s1-q11-a.html

^ that is the link with the question on it. the question specifically i don't understand is 11.3, stating:

The pregnancy test strip will show a positive test result when a woman is pregnant.
Explain how the pregnancy test strip works to show a positive result. [6 marks]

the mark scheme is underneath as well.
it's not very clear on the stages in the mark scheme, so i am quite confused which hormone goes to where.

i'd appreciate it if you could perhaps explain the mark scheme answer in a more easier and approachable format? (dumb it down for all i care, i'm just trying to understand!)

thank you :smile:

gods, ive had this question in a mock before and jesus christ is it a *****. not sure if im going to be much clearer but ill try!

so the first thing is that bc of the blue dye on the antibodies, when there's lots of them they'll form a blue line.
1. so the urine of a pragnant woman contains a hormone called HCG -- only pregnant women
2. so when a pregnant woman pees on the test and the urine moves up the stick (absorption/diffusion -- you dont really need to know) the HCG hormone moves up too
3. in the 'reaction zone' there are antibodies specific to HCG that can move, so when the urine reaches it, the HCG binds so the antibodies and they move too
4. HOWEVER there are more antibodies than molecules of HCG, so some of the antibodies moving up are 'empty'
5. then in the 'results window' the HCG also binds to the antibodies that cant move, while still being attached to the others, so a blue line forms
6. but the empty antibodies keep going and attach to Another set of antibodies (which cant move) specific to the original ones, which creates another blue line

the language on the markscheme is more concise for exams, but hopefully this will make it easier to understand :smile:
Original post by Amicia3
gods, ive had this question in a mock before and jesus christ is it a *****. not sure if im going to be much clearer but ill try!

so the first thing is that bc of the blue dye on the antibodies, when there's lots of them they'll form a blue line.
1. so the urine of a pragnant woman contains a hormone called HCG -- only pregnant women
2. so when a pregnant woman pees on the test and the urine moves up the stick (absorption/diffusion -- you dont really need to know) the HCG hormone moves up too
3. in the 'reaction zone' there are antibodies specific to HCG that can move, so when the urine reaches it, the HCG binds so the antibodies and they move too
4. HOWEVER there are more antibodies than molecules of HCG, so some of the antibodies moving up are 'empty'
5. then in the 'results window' the HCG also binds to the antibodies that cant move, while still being attached to the others, so a blue line forms
6. but the empty antibodies keep going and attach to Another set of antibodies (which cant move) specific to the original ones, which creates another blue line

the language on the markscheme is more concise for exams, but hopefully this will make it easier to understand :smile:

ahh thank you! this is a lot better to understand! i appreciate it so much :smile:
Original post by harlz_chalamet
ahh thank you! this is a lot better to understand! i appreciate it so much :smile:

no problem and good luck!!

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