In comparing phloem and xylem, which statement best describes phloem function?

• A. Xylem transports water and minerals.
• B. Phloem transports sugars and other organic nutrients from sources to sinks; xylem carries water and minerals.
• C. Phloem transports water upward.
• D. Phloem transports sugars from sources to sinks; xylem carries water and minerals.

Answer: (B)

Phloem’s job is to move the products of photosynthesis—mainly sugars and other organic nutrients—from where they’re produced or stored (sources) to where they’re used or stored (sinks). This transport involves living phloem tissue and a mechanism (often described by the pressure-flow concept) that can push sap in multiple directions depending on the plant’s needs, such as distributing sugars to growing tissues or to storage organs. Because of this, the best description emphasizes both the type of material moved (sugars and other organic nutrients) and the direction from sources to sinks.

Xylem, by contrast, is the tissue that carries water and dissolved minerals from the roots up through the plant, usually in one main direction. So the statement that phloem transports sugars and other organic nutrients from sources to sinks, while xylem carries water and minerals, captures the true functional relationship between these two tissues. The other options either attribute phloem’s role to transporting water or describe movement that doesn’t fit phloem’s primary function.