Any biology help..please need it right now!!!

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Asphyxiating
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Can someone look at Q9 on page 8 of this page:

http://www.iob.org/downloads/Part%20Awebsite.pdf

The answer is D but I can't understand why, can someone explain what is going on?? Thanks! I really appreciate it..
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madmazda86
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8. Which hypothesis seeks to explain why a plant auxin produces different effects
on the growth of a root and of a shoot?
A. Gravity affects the action of the auxin.
B. The growth rates of roots and shoots differ.
C. The auxin travels faster downwards towards the root.
D. The root and shoot respond differently to similar auxin
concentrations.
E. Light affects the action of the auxin.

You can explain this by ruling the others out. As you're trying to explain why plant auxin produces different effects on root/shoot growth, it can't be down to growth rate as auxin doesn't affect this (it affects direction, not growth itself as growth is caused by dividing cells.). So that rules out B.

Gravity does affect the action of auxin but if that were totally the case then the shoot would grow downwards like the root (geotropism). But it doesn't so therefore other factors must be involved, thus ruling out A.

For the same reason you can also rule out C - if C were true then the shoots would grow downwards again.

Plant shoots grow towards light because auxin concentrations increase on the light-exposed side (phototropism) but plant roots don't do this because there's little light below the soil. So it explains shoot growth but not root growth, and you're after one that explains both. So that rules out E, leaving D!

Hope that helped
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Asphyxiating
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Sorry, it's the one below it, could you help me with it? Q9
Thanks so much!!
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madmazda86
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D'oh! Sorry - it's late

D. species II has a higher respiration rate than species I

This would be because only at the highest light intensity did the indicator start changing colour to purple for Species II. As respiration absorbs oxygen, this would have kept the indicator red as long as the rate of O2 absorption by respiration exceeded the amount of O2 production by photosynthesis. At the higher light intensity the rate of photosynthesis increased to the point where it exceeded the rate of respiration. Thus more O2 is being released in photosynthesis than is being absorbed in respiration, and thus the indicator colour changed to purple/red.

For Species I, however, the colour change purple/red occurred at the lowest light intensity and stayed purple as the light intensity increased. This would indicate a lower respiration rate as it was easier for the rate of photosynthesis to exceed the respiration rate enough to release more O2 than was being absorbed, even at the lower light intensity.

I think that's how it goes, though it could be applied to the CO2 absorption in photosynthesis and the CO2 release in respiration too - either one would work in theory, though it's probably one or the other with a bicarb indicator (I don't really know how they work.) Does that make sense? I tend to be a bit long-winded with my explanations
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Asphyxiating
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Ok that makes sense! But I thought Bicarbonate indicator solution was a measure of carbon dioxide? So would that make it the opposite of your oxygen conclusion..but then there would be less CO2 produced in light in species I, but the solutions are purple..so this has made me confused again! Sorry! What does the purple indicate? That carbon dioxide is present? Or have I got this all muddled up?! Thanks so much for your help!!
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madmazda86
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Zzzzzz.... sorry, I really do know sodall about how bicarb indicators work. Those are the general principles anyway - though I'd say it's an oxygen indicator as it wouldn't work the other way around... I think. I neeeed sleep!
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Asphyxiating
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It's ok, i'm getting pretty tired now too, I need sleep! I think I shall give up soon Thanks so much for your help anyway, I wish I knew half as much as you know!
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