The movement of materials already in the phloem can be described using the term(s) ____.

A) source-to-sink only
B) pressure flow only
C) cohesion only
D) both active transport and cohesion
E) both source-to-sink and pressure flow

The movement of materials in the phloem involves both source-to-sink transport (movement from source tissues to sink tissues, where materials are used or stored) and pressure flow (the movement of materials due to differences in pressure gradients along the phloem). Both of these processes are involved in the movement of materials already in the phloem. Cohesion is not directly involved in the movement of materials in the phloem, but rather plays a role in the movement of water in the xylem. Active transport may be involved in loading materials into the phloem, but is not directly involved in the movement of materials already in the phloem.