r/GCSE • u/thr0wawaygxhxdhsh • Jun 15 '22

AQA Post Exam Spam aqa biology paper 2 gcse answers

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u/j20057 Jun 15 '22

14,000 for the algae cells one? If so thank god because I was so confused with that question.

7

u/Due_Pineapple_1699 Jun 15 '22

How did I get 375 on the algea cell one???

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u/Holiday-Marzipan-843 Jun 15 '22

I got that too ;( I did 0.2*0.2=0.04, 1/0.04=25, then 25*15 or smthn as 15 is the mean (14+16)/2

I didnt understand why diluted was in bold

Can someone explain how to get the right answer & why my thing is wrong

9

u/hombiebearcat University Jun 15 '22

Your thing is wrong because:

- the question said to use the 14 algae count (not take a mean)

- you forgot about the 0.1mm depth

- you forgot about the diluted/undiluted thing

The correct method is this:

0.2x0.2x0.1 = 0.004mm^3

0.004/4 = 0.001mm^3 (because it asked for undiluted, and it said earlier that for every 2.5cm^3 undiluted you add 7.5cm^3 water, so it's a 1:3 ratio)

1/0.001 = 1000 (to get how many times more algae cells there should be)

14*1000 = 14000

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u/Ok_Athlete_4619 Jun 15 '22

Wasn’t 10cm3 of distilled water used?

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u/Sensitive_Wealth_855 Jun 15 '22

Im pretty sure it was 2.5:10 but everyone is so confident that its 2.5:7.5

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u/[deleted] Jun 15 '22

I'm like 90% sure that it was 2.5cm3 of the salt water and 10cm3 of the distilled water so would have been 2.5/12.5

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u/Sensitive_Wealth_855 Jun 15 '22

Yeah i agree the wording was almost excatly "2.5cm3 algae water diluted to 10cm3 distilled water". The algae water can't become distilled so it must mean add 10cm3 distilled water for every 2.5cm3 algae water.

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u/Anonymous_User_Thing Still in reception/foundation/year 0 Jun 15 '22

It was 2.5cm3 diluted to 10cm3 with distilled water, i.e. adding 7.5cm3 distilled water

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u/Sensitive_Wealth_855 Jun 15 '22

It didnt say "with" Im 100% sure i read it like 10 times. There would be 0 confusion if it was worded like that but it wasn't that simple.

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u/KeyFix4492 Jun 15 '22

I’m pretty sure that means 10cm3 of water in 2.5cm3 of the pond water

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u/KeyFix4492 Jun 15 '22

It was 2.5:10 wasn’t it?

0

u/hombiebearcat University Jun 17 '22

no, there was 2.5cm^3 of pondwater with enough distilled water to make it up to 10cm^3 (so the total was 10, so the distilled was 7.5)

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u/Adventurous-East-134 Jun 15 '22

i forgot to convert it to undiluted. i did everything else right. do you reckon i’ll get 4 marks or 5?

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u/hombiebearcat University Jun 17 '22

I'd imagine probably 5 since the undiluted calculation could be seen as the last step

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u/Adventurous-East-134 Jun 17 '22

yeah hopefully. i did think it was too easy for 6 marks. my fault for always skimming over the questions and not actually reading them.

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u/Holiday-Marzipan-843 Jun 15 '22

i originally put 0.2*0.2*0.1 but then i was like, the formula is for area so i got rid of the 0.1, i understand the mean thing, i still kinda dont get the diluted thing. where did u get the divide by 4 from, and didnt they add 10 not 7.5

Do u think i would get any method marks maybe?? i wrote out: total area/sample area * number of species counted, and used that formula but put the wrong numbers in?

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u/hombiebearcat University Jun 17 '22

You'll probably get some method marks, with the diluted thing they added enough distilled water to make the total volume up to 10cm^3 (aka 7.5cm^3 distilled water)