sap is a fluid that moves in either the xylem or phloem vascular system of a plant. Xylem sap is a watery solution of minerals taken up from the soil by the roots. It moves in xylem cells (vessel elements, tracheids) that form long rows of cylindrical pipes. The flow is driven by evaporation from the leaves, and a large tree can easily take up more than 100 liters of water a day in this way. Plants go through the trouble of extracting water from the soil with one primary goal: producing sugar. Most of the water is lost while obtaining carbon dioxide from the atmosphere and in photosynthesis, a process that converts light energy into chemical energy and stores it in the bonds of sugar molecules. Plants use phloem sap to distribute the energetic sugars throughout the organism, where they are used in growth and metabolism, and for producing sweet fruits such as apples. The liquid flows in sieve element cells, which form a channel network running throughout the plant. Phloem sap contributes to many natural sweeteners, such as flower nectar and palm sugar. See palm sugar.