Transport in plants
Xylem, phloem and water uptake
Plants have two transport tissues in vascular bundles. Xylem carries water and mineral ions up from the roots; its vessels are dead, hollow tubes with no end walls and thick walls strengthened with lignin, which also support the plant. Phloem carries sucrose and amino acids, both up and down, from where they're made or stored (sources) to where they're needed (sinks). Water enters root hair cells by osmosis, crosses the root cortex to the xylem, and travels up to the leaves.
≈ 30 minTranspiration and translocation
Transpiration is the loss of water vapour from leaves: water evaporates from mesophyll cell surfaces into air spaces, then diffuses out through the stomata. This pulls a continuous column of water up the xylem (the transpiration stream), because water molecules stick together (cohesion). Transpiration is faster when it is hotter, drier (low humidity), windier and brighter (more stomata open). It's measured with a potometer. Translocation moves sucrose and amino acids in the phloem from sources (leaves, storage organs) to sinks (growing points, roots, fruits).
≈ 40 min