sugar is conducted through specialized cells known as
1 Sugar diffuses from the mesophyll in the leaf to the phloem cells in the vascular bundles. 2  Specialized cells called companion cells load the dissolved sugar into the sugar-conducting cells (called sieve elements) of the phloem by using cellular ATP as an energy source. - collections of similar cells that serve a specific purpose by functioning together. 2  Unlike animals, the major organs of plants (roots, stems, and leaves) are all composed of the same three tissues (epidermis, vascular tissues, and ground tissues).