All living cells require water and nutrients. If an organism is a single cell or if its body is only a few cells thick, water and nutrients are easily moved through the organism by diffusion. However, diffusion is generally too slow for even small plants to meet their water and nutrient needs. In plants, this problem was solved with the evolution of a specialized system for fast and efficient long-distance transport of water and nutrients. This specialized cellular network is the vascular tissue system; plants with vascular tissues are referred to as vascular plants.

The vascular tissue system is composed of two different types of tissues: xylem and phloem. Although both xylem and phloem form a continuous tissue system throughout the plant body, the two tissues have different functions. Xylem is the primary water- and mineral-conducting tissue, and phloem is the primary food-conducting tissue.

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