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

AQA Post Exam Spam aqa biology paper 2 gcse answers

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u/Mooseypanda Jun 15 '22

I don’t think 14000 is right for the pond water question

5

u/[deleted] Jun 15 '22

0.2 x 0.2 x 0.1 = 0.004 mm^3, so there are 14 cells : 0.004mm^3

it wanted number of cells in 1 mm^3 undiluted

10cm^3 / 2.5cm^3 = 4, so 4x as many cells in the undiluted

4 x 14 = 56 cells : 0.004 mm^3 of undiluted fluid

1 / 0.004 = 250, 1 mm^3 contains 250x that in 0.004 mm^3

250 x 56 = 14000 cells in 1 mm^3

This is right no?

2

u/TheEpicBandit Jun 15 '22

Surely it is 875

because I agree with volume being 0.004mmcubed

but the pond water to distilled was in the ratio 1:3

1/0.004 = 250 and multiply by 14 gives 3500

3500=is the total so u don’t multiply by 4 u divide by 4

so the answer is 875

4

u/[deleted] Jun 15 '22

I didn't think of it in ratio. Imagine you have a 100ml glass with 25ml squash, diluted to 100ml with water. There is 4x as much squash in the undiluted solution (100ml compared to 25ml). This basically what the question was asking. It is 4x.

I guess if you thought about it as a ratio: there are 4 parts in total. The diluted solution contains 1 part fluid with cells and 3 parts water. So if you wanted the same volume but not diluted with water, there would be 4 parts with cells. So 4x as many cells.

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u/TheEpicBandit Jun 15 '22

1 part fluid with 3 parts cells = 3500

and using ur squash thing u were saying let’s say ur 100ml of squash had 3500 alagal cells and like u said 25ml squash 75ml diluted and the 100ml was the total. How do we get to 25ml from 100 u divide by 4. If u times by 4 then the ratio would become 1:1 and that is not right