What is translocation in plants?

• A. Movement of sucrose and amino acids through the phloem from production to storage or to respiration or growth
• B. Movement of water through the xylem
• C. Gas exchange
• D. Photosynthesis

Answer: (A)

Translocation is the movement of soluble nutrients, mainly sucrose, through the phloem from places where they are produced or stored (sources) to places where they are used or stored (sinks), such as growing tissues, fruits, or roots. This transport uses bulk flow: sugars are actively loaded into phloem at the source, which draws in water by osmosis and creates a hydrostatic pressure that pushes the sap through the sieve tubes toward sinks. When the sugars reach a sink, they’re unloaded for growth, respiration, or storage, and the pressure drops, helping to pull more sap along from other sources. Because it depends on the location of sources and sinks, the flow can move in either direction.

This is different from the movement of water through the xylem, which is driven largely by transpiration and root pressure and moves water upward from roots to leaves. Gas exchange involves stomata and the exchange of CO2 and O2, not nutrient transport. Photosynthesis is the process that makes the sugars that later get moved by translocation.