I have no idea how to answer this question so I thought this would be a good one for Chat GPT. I don’t know if its answer is correct. Chat GPT always presents a follow up question to engage the reader. I included it.
Good question — let’s break it down carefully.
First:
How fast do photoassimilates move through the phloem?
• In trees and other plants, phloem sap moves at about 0.5 to 1.0 meters per hour on average.
• In some plants under optimal conditions, speeds can reach up to 1–2 cm per minute, which is about 1.2 meters per hour.
It’s much slower than, say, blood flow in animals, but it’s still quite steady. In very tall trees, it can take hours to days for sugars to move from leaves at the top down to roots.
Does gravity assist the movement?
• No. Phloem transport is driven by pressure differences — not gravity.
• The process is called pressure-flow (or the Münch hypothesis).
• Sugars made in the leaves (“source”) are loaded into phloem cells, which draws water into the phloem from the nearby xylem (osmosis).
This builds up turgor pressure at the source.
• At the “sink” (e.g., roots, fruits, growing tissues), sugars are unloaded, which lowers the pressure.
• This pressure difference pushes the phloem sap through the plant, regardless of direction — up, down, sideways.
Gravity does not speed it up, and phloem can even move sugars upward against gravity when needed.
Does phloem move faster or slower than gravity?
• Gravity is “instantaneous” (things fall at ~9.8 m/s²), so gravity-driven movement would be much faster if that were the mechanism.
• Since phloem flow relies on pressure gradients and osmotic processes, it’s much slower than free-falling objects under gravity.
In short:
• ~0.5–1.0 meters per hour in trees.
• Gravity does not assist phloem movement.
• Phloem moves much slower than gravity would move something.
Would you like me to also explain how environmental factors (like drought or cold) can slow or change phloem speed in trees? It’s pretty interesting, especially for big trees!
