The increase in pressure potential at the source end of the sieve tube is caused by the uptake of water.The water enters the sieve tubes through

Question

Quizplus · Accepted Answer

The uptake of water into the sieve tubes is due to osmosis, as water moves from an area of higher water potential in the surrounding cells into the sieve tubes where the water potential is lower. This movement of water generates pressure potential, which increases at the source end of the sieve tube, driving the movement of sugars and other solutes through the phloem towards the sink. Active transport, bulk flow, and translocation also play a role in phloem transport, but they are not directly responsible for the increase in pressure potential at the source end. Gravity does not typically contribute to phloem transport.

The Increase in Pressure Potential at the Source End of the Sieve