What is the primary function of phloem tissue?

• A. Transport of sugars and other photosynthates from source to sink
• B. Structural support
• C. Water transport
• D. Storage of nutrients

Answer: (A)

The main idea here is that phloem moves sugars and other photosynthates from where they’re made or stored (sources) to where they’re needed or stored (sinks). Phloem tissue is the part of the plant’s vascular system that carries this nutrient-rich sap, using sieve tube elements that work with companion cells. At a source, sugars like sucrose are loaded into the phloem, which draws water from nearby xylem by osmosis and creates a bulk flow that pushes the sap through the sieve tubes toward sinks such as growing tissues, roots, or developing fruits. When the sap arrives, sugars are unloaded and used for growth or stored.

This is different from xylem, which mainly transports water and minerals from roots upward and contributes to support through its rigid, lignified cells. While phloem can contain storage cells, storing nutrients is not its primary job; its primary role is distribution of sugars and other photosynthates throughout the plant.