Control in plants-hormones GCSE AQA Biology Unit 1

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tkrv
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Can someone please tell me what the auxin does in phototropism and gravitropism please?
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JoeZei
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Photo tropism means a part of the plant grows towards the light, and gravitropism means part of the plant (the root) grows with gravity. if thats what your asking....
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Federerr
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(Original post by tkrv)
Can someone please tell me what the auxin does in phototropism and gravitropism please?
I did this last year not really fresh in my head..

I believe the cells on the tip of shoot detects light stimulus and causes auxin to be produced. The auxin moves to the shaded region of the stem causing that side of the stem to elongate faster compared to the non-shaded side. This is the reason the shoot bends towards the light. (Phototropism)

For gravitropism, all I know is that the root bends towards water and minerals/ions. I don't really know why.

Correct me if im wrong
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MersennePrime
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Phototropism
This means that the shoots in a plant towards the light. In shoots, auxin stimulates growth. Auxin accumulates on the side with the least light. This means that the side with the auxin on grows faster compared to the side with more light. As there's an unequal rate of growth in the sides, it causes the shoot to bend towards the light.

Gravitropism
This means that the roots grow towards gravity. In the roots, auxin inhibits growth. Due to the natural nature of gravity, auxin accumulates on the lower side of the root. This means that there, again, is an unequal rate of growth on both sides of the root. The top (side with no auxin) grows faster, while the side with auxin in grows slower. This means that the root bends downwards, towards the gravity and in the opposite direction of the shoots.

If you need any more help, feel free to ask
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tkrv
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(Original post by MersennePrime)
Phototropism
This means that the shoots in a plant towards the light. In shoots, auxin stimulates growth. Auxin accumulates on the side with the least light. This means that the side with the auxin on grows faster compared to the side with more light. As there's an unequal rate of growth in the sides, it causes the shoot to bend towards the light.

Gravitropism
This means that the roots grow towards gravity. In the roots, auxin inhibits growth. Due to the natural nature of gravity, auxin accumulates on the lower side of the root. This means that there, again, is an unequal rate of growth on both sides of the root. The top (side with no auxin) grows faster, while the side with auxin in grows slower. This means that the root bends downwards, towards the gravity and in the opposite direction of the shoots.

If you need any more help, feel free to ask
thanks so much!! really helps!!
but can you explain gravitropism as negative and positive please. i'm quite confused with gravitropism ://
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Sarahtoninx
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(Original post by tkrv)
thanks so much!! really helps!!
but can you explain gravitropism as negative and positive please. i'm quite confused with gravitropism ://
Positive tropism is where part of the plant grows TOWARDS the stimulus.

Negative tropism is where part of the plant grows AWAY FROM the stimulus.

So in terms of gravitropism, the roots show POSITIVE GRAVITROPISM because the roots of a plant grow towards (in the direction of) gravity, and the shoots show NEGATIVE GRAVITROPISM because they grow away from (against) gravity.

Hope this helps
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