The hypothesis accepted for the translocation of sugar from source to sink is _____ (a) Cohesion hypothesis (b) Mass flow hypothesi (c) Malate hypothesis (d) Donnan hypothesis
Answers
"(b) Mass flow hypothesis
""Mass flow hypothesis"" is the hypothesis which explains transport of sugar from the sites of photosynthesis to the sinks such as root and stem tips.
At the leaves, the glucose are ""converted into sucrose"" and are taken up by active transport into the ""phloem sieve tube"" cells.
Due to increased ""osmotic pressure"" at the ""source"", the sieve cells move towards sites of lower osmotic pressure which are the sinks.
On reaching the sink, the sugars are transferred to the cells from the sieve tubes by active transport. This process reduces the osmotic pressure and thus ""water moves out"" of the ""phloem"".
As a result, the hydrostatic pressure increases in the phloem and due to pressure flow, sap flows through the phloem. This also produces a ""high water potential"" at the phloem due to active removal of solutes and so the water flows onto the xylem."