In Phloem, Photosynthetic Products Can Move Both Laterally and Vertically

Multiple Choice

In phloem, photosynthetic products can move both laterally and vertically. Therefore, the protoplasmic strands that link adjacent sieve tube elements are

A) actively opened and closed in response to phytochemical messages.
B) located on sieve tube plates on end walls.
C) located on sieve areas on side walls.
D) largely absent.
E) located on sieve tube plates on end walls and sieve areas on side walls.