z4_
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Hi everybody,
I was just doing an aqa a level biology specimen paper, and I came across a question which shows a graph with the uptake of chloride ions in barley plants. It asks you to work out the ratio of the mean rate of uptake of chloride ions in the first hour to the rate of uptake of chloride ions in the second hour for group b plants. The answer box already has :1 in it.

My (wrong) working
1) The graph shows that 360 chloride ions are taken in the first hour. I divide this by 60 to get 60 as the rate of uptake
2) The graph shows 470 ions taken in overall over two hours. I do 470-360=110 to get uptake in second hour
3) Divide 110 by 60= 1.833

I don't really know what to do next, and I think I may have done it wrong so far. The mark scheme gives the answer as 3:3:1, giving no further idea as to how to work it out . If anybody can help it would be greatly appreciated. Thanks in advance .
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RMNDK
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(Original post by z4_)
Hi everybody,
I was just doing an aqa a level biology specimen paper, and I came across a question which shows a graph with the uptake of chloride ions in barley plants. It asks you to work out the ratio of the mean rate of uptake of chloride ions in the first hour to the rate of uptake of chloride ions in the second hour for group b plants. The answer box already has :1 in it.

My (wrong) working
1) The graph shows that 360 chloride ions are taken in the first hour. I divide this by 60 to get 60 as the rate of uptake
2) The graph shows 470 ions taken in overall over two hours. I do 470-360=110 to get uptake in second hour
3) Divide 110 by 60= 1.833

I don't really know what to do next, and I think I may have done it wrong so far. The mark scheme gives the answer as 3:3:1, giving no further idea as to how to work it out . If anybody can help it would be greatly appreciated. Thanks in advance .
"The graph shows that 360 chloride ions are taken in the first hour. I divide this by 60 to get 60 as the rate of uptake"

\dfrac{360}{60} \not= 60

Now you've got ___: 1.8333...

Divide by 1.83333....

And there's your answer!
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z4_
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(Original post by RMNDK)
"The graph shows that 360 chloride ions are taken in the first hour. I divide this by 60 to get 60 as the rate of uptake"

\dfrac{360}{60} \not= 60

Now you've got ___: 1.8333...

Divide by 1.83333....

And there's your answer!
Oops! I wasn't thinking straight with the 60 there. Anyway, if I now have 6:1.8333, and I divide this by 1.83333, then I get 3.27:1. I'm still confused - maths is my weak point as you can tell .
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RMNDK
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(Original post by z4_)
Oops! I wasn't thinking straight with the 60 there. Anyway, if I now have 6:1.8333, and I divide this by 1.83333, then I get 3.27:1. I'm still confused - maths is my weak point as you can tell .
Isn't that the answer?

I thought you said the answer given was 3:1

So you can just round 3.27 to 3?

Or does it say something else like (to 1 d.p)?
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z4_
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(Original post by RMNDK)
Isn't that the answer?

I thought you said the answer given was 3:1

So you can just round 3.27 to 3?

Or does it say something else like (to 1 d.p)?
The answer given is 3: 3: 1 and the question doesn't mention to how many decimal points the answer should be given to
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RMNDK
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(Original post by z4_)
The answer given is 3: 3: 1 and the question doesn't mention to how many decimal points the answer should be given to
Now I'm confused..

Why is it 3 to 3 to 1? You're only finding the ratio between two things, mean rate in first hour against mean rate in second hour. Where's this third variable?

I really can't help you much further then because I don't know what the mark scheme is on about...

Could you link the mark scheme (and paper with the question), that might be of use?
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z4_
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(Original post by RMNDK)
Now I'm confused..

Why is it 3 to 3 to 1? You're only finding the ratio between two things, mean rate in first hour against mean rate in second hour. Where's this third variable?

I really can't help you much further then because I don't know what the mark scheme is on about...

Could you link the mark scheme (and paper with the question), that might be of use?
Its a specimen paper for the new spec, here's the link:
http://filestore.aqa.org.uk/resource...-74021-SQP.PDF
http://filestore.aqa.org.uk/resource...-74021-SMS.PDF

The question number is 5.2

Thanks again for taking the time to help me
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RMNDK
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(Original post by z4_)
Its a specimen paper for the new spec, here's the link:
http://filestore.aqa.org.uk/resource...-74021-SQP.PDF
http://filestore.aqa.org.uk/resource...-74021-SMS.PDF

The question number is 5.2

Thanks again for taking the time to help me
Wait, the mark scheme says the answer is indeed 3.3 : 1 and not 3 : 3 : 1.
That's what we should be getting.


Are you sure this is the mark scheme, or did you just misread it??
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sofia.aa
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At first hour (60 minute) the uptake is 360At second hour (120) it increase to 470 but that doesn't tell us the exact uptake for the second hour so we do 470-360= 110Now we know that at second hour the uptake of chloride ions was 110so, then we do 360/110= 3.27now we need to round it so that it become 3.3overall: 3.3:1
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Aswathy Nishad
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in the first hour mean chlorine uptake is 360 /60= 6in the second hour (470-360)/ 60= 110 / 60=1.833now the ratio we get is 6: 1.833On dividing both the numbers by 1.833 , we get the new ratio as, 3.27 : 1 which can be rounded to 3.3 : 1
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