 We're nearly there. We know how water moves up the plant in the xylem, with some minerals dissolved in the water, and we know that sugars move up and down the plant in the phloem. So all that is left to discover is exactly how the phloem works. We had the transpiration stream and the transpiration pool in the xylem, but there are no forces causing translocation, so something different must happen in the phloem. The phloem uses active transport to transport the food nutrients like glucose and amino acids around the plant. If you have forgotten how that works, watch our video on diffusion, osmosis, and active transport first. Glucose is made in the leaves by photosynthesis. Glucose is converted into sucrose in the leaves, which then enters the phloem vessels, as do amino acids. They then need to be transported around the plant to every single cell. The areas of the plant where sucrose is made are called the sources, and where they are delivered are called sinks. The phloem uses active transport because the sucrose moves against its concentration gradient, from the lower concentration where it is made to a higher concentration in the phloem cells. We don't need to know much about the phloem, but just be aware that they contain sieve tube plates, which the phloem sap travels through. The neighboring companion cells provide the sieve tube elements with the energy they need for the active transport. So in these three videos, we have learnt all about the transport of water and minerals through the plant via the xylem. The transpiration of water and the leaf creates a transpiration pool, which almost physically pulls the water up through the plant. Just picture pulling water up from a well, and that is what is happening. We then also learnt about the energy driven translocation of sugars and amino acids in the phloem. Whereas water only travels in one direction, from the roots to the leaves, the sugars and amino acids are needed by every single cell, and so the phloem is multi-directional. But to achieve this, active transport and energy is needed.