AP BIOLOGY

Detailed explanation-1: -From the companion cells, the sugar diffuses into the phloem sieve-tube elements through the plasmodesmata that link the companion cell to the sieve tube elements.

Detailed explanation-2: -Food is synthesized in the green parts of a plant. The non-green parts are depended on the photosynthetic cells for nourishment. The food in the form of sucrose is transported by the vascular tissue phloem.

Detailed explanation-3: -Within the phloem, sugars migrate to regions of low osmotic concentration and low water pressure, called sinks, from areas of high osmotic concentration and high water pressure, known as sources.

Detailed explanation-4: -Phloem parenchyma cells, called transfer cells and border parenchyma cells, are located near the finest branches and terminations of sieve tubes in leaf veinlets, where they also function in the transport of foods.