Vascular Plant: Any of various plants that have the vascular tissues xylem and phloem. The vascular plants include all seed-bearing plants (the gymnosperms and angiosperms) and the pteridophytes (including the ferns, lycophytes, and horsetails). Also called tracheophyte.1

How is sugar actively transported into the phloem? There are two known mechanisms:

  • In the first mechanism, sucrose enters the cell walls near the phloem in the smallest (minor) veins of the leaf. It then enters the phloem by attaching to sucrose transporter proteins embedded in the plasma membranes of the sieve elements and companion cells.2

  • In the second mechanism, sucrose enters the companion cells of the minor vein through small plasmodesmata, and is converted to larger sugars, raffinose, and stachyose. These larger sugars are unable to diffuse back through these plasmodesmata due to their size. Therefore they are trapped in the Phloem of the leaf and build up to high concentration. They enter the sieve elements through larger plasmodesmata and are carried away toward the sinks. 2

  • When sugars and other nutrients arrive in sink tissues they unload from the phloem and enter surrounding cells, either through plasmodesmata or by crossing from one cell to another across the cell walls. The size and metabolic activity of the different sinks determines the amount of material that is delivered to them.2

  • Thus, the use of sugar in the sinks determines how much sugar flows to them.

Sieve tubes, companion cells, phloem parenchyma, bast fibers, intermediary cells
Tracheids, vessel elements, xylem parenchyma, xylem sclerenchyma
Nature of tissue:
Living tissue
Non living tissue at maturity
Unidirectional (upward)
Transportation of food and nutrients from leaves to storage organs and growing parts of plant.
Water and mineral transport from roots to aerial parts of the plant.
Tubular with soft walled cells
Tubular with hard walled cells
Moves up or down the plant's stem from "source to sink"
Moves up the plant's stem
Roots, stems and leaves
Roots, stems and leaves
Additional Functions:
Forms vascular bundles with xylem
Forms vascular bundles with phloem and gives mechanical strength to plant due to presence of lignified cells.3

Figure 2. Transport of Sugars In Vascular Plants
Figure 2. Transport of Sugars In Vascular Plants

Vascular plants evolved in the Silurian and Devonian periods approximately 400 million years ago. 4
Scientists classify vascular plants by their ability to produce seeds. Therefore, two distinct groups are seed-producing and non-seed-producing types. A fern is an example of a non-seed producing vascular plant whereas grass is an example of a seed-producing type. 5

What do you know about Transport of Sugars In Vascular Plants?
1. Describe the function of xylem and phloem tissue?
2. Describe the 2 mechanisms of how sugar is transported into the phloem.
an organism capable of self nourishment by using inorganic materials as a source of nutrients.3
a phloem cell with pores in its cell walls; contains all necessary cell organelles.1
the part of a vascular bundle consisting of sieve tubes, companion cells, parenchyma, and fibres and forming the food-conducting tissues of the plant.3
any of many minute stands of cytoplasm that extends through plant cell walls and connect adjoining cells.2

1. Translocation - Biology Encyclopedia - cells, plant, body, function, process, system, different, organs, used
2. [[ of Sugars.html#ixzz1xmE5g213| of Sugars.html#ixzz1xmE5g213]]
3. Nelson Biology 11. LeDrewB. FraserD. DulsonJ. Nelson Education Ltd. Pages 568-570 Transport of Sugars.
4. Fun Facts About Seedless Vascular Plants |
5. Defining Characteristics of Vascular Plants |