Final answer:
The true statement about xylem and phloem transport is that both rely on a water potential gradient. Xylem transport is a passive process that moves water upwards, and phloem actively transports nutrients in both directions depending on the location of source and sink areas.
Step-by-step explanation:
The correct answer to the question, 'Which of the following statements about xylem and phloem transport is true?' is that both rely on a water potential gradient. While the xylem transports water up from the roots through the process of transpiration pull, which is a passive process driven by water evaporation from the leaves creating a negative pressure or tension, the phloem transports nutrients like sugars from source to sink regions. This involves a process called phloem loading, which is an active process requiring energy in the form of ATP to accumulate sugars in the sieve tube elements, resulting in water flowing into these elements, increasing the pressure, and driving the flow towards sink areas. Phloem transport can occur both upwards and downwards depending on where the nutrients need to go, unlike the unidirectional transport in xylem which is only upwards from roots to leaves. It's important to note that xylem transport is facilitated by bulk flow through non-living cells, whereas phloem transport involves bulk flow through living sieve tube cells interconnected by plasmodesmata.