horiphin
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I'm having a bit of trouble understanding the answers for this question:

Invertase breaks down sucrose into glucose.
In modified plants where invertase is inserted into the potato tubers, the unloading of sucrose is increased in the tubers compared with those that were not modified.
The transport of sucrose to the tubers was also increased in the modified plants.
Deduce a possible mechanism for the increased unloading and transport of sucrose in the modified plants. (4 marks)

I got the first two marks by saying that there is less sucrose at the sink due to it being broken down into glucose, which increases the sucrose concentration between the source and sink, but the answers also say that the solute gradient is increased and water removal from the phloem increases pressure gradient between source and sink. Surely that shouldn't be contributing to more unloading, since there will be more solute at the sink, which means less water will diffuse out instead of more water being removed from the phloem, which would decrease the pressure gradient?
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AbiCEyre
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Would co-transport get you a mark as that's how glucose is transported into and out of cells?
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Inister
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There will be less solute at the sink. The sucrose will be broken down into glucose, which will exit the phloem and will be taken up by cells. Water follows the glucose out of the phloem by osmosis. Therefore, the phloem at the sinks will have a lower pressure than the sources, so the gradient is increased, so mass flow of sucrose increases
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horiphin
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(Original post by Inister)
There will be less solute at the sink. The sucrose will be broken down into glucose, which will exit the phloem and will be taken up by cells. Water follows the glucose out of the phloem by osmosis. Therefore, the phloem at the sinks will have a lower pressure than the sources, so the gradient is increased, so mass flow of sucrose increases
Thank you so much!!
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horiphin
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(Original post by AbiCEyre)
Would co-transport get you a mark as that's how glucose is transported into and out of cells?
Ah, there was nothing in the mark scheme about co transport specifically
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