What are xylem and phloem in plants, and what do they do?

Plants, like us, need food and water to survive. We have a heart, arteries and veins that help us circulate our blood around. But plants don't have that, and need ways of transporting water and food, which they do through xylem and phloem. Both xylem and phloem are long continuous tubes made by rows of cells. Water is absorbed by plants through the roots, and it needs to be transported from there to the rest of the plant. The xylem, a long tube, moves water and solutes, from the roots all the way to the leaves. This process is called transpiration. Plants need glucose and amino-acids for survival. Plants make glucose in the leaves with photosynthesis and it is converted in sucrose. The phloem, also a long tube, moves sucrose and amino acids from the leaves all around the plant. This process is called translocation. 

The xylem and phloem are arranged in clusters called vascular bundles. They have a specific arrangement, which is slightly different in the roots to the stems. The xylem are made up of dead cells containing lignin - a woody material that makes the walls thick and stiff. This makes xylem impermeable to water and allows it to transport water. Xylem moves the water upwards - only one way, from the roots to the leaves by transpiration. Transpiration is the evapouration of water from the leaves and stems of the plant. Imagine a long string of beads - this is how water droplets stick to each other and move up the plant in the xylem. When this water evapourates out of the leaves, a suction pressure is created pulling the rest of the water through the plant. This pull is called the transpiration pull. On the other hand, the phloem is made up of living cells which have "end walls with perforations". Phloem transport sucrose and amino-acids both up and down the plant, depending on where they are needed via translocation. The leaves, that produce sucrose and amino acids are called "sources" and the places they are delivered are called "sinks". Active transport (means it uses energy) pushes the sucrose from the leaves into the phloem against the concentration gradient.