Transport in Plants

Plant transport begins with diffusion, osmosis, and active transport. Water movement is best understood with water potential, and water always moves from higher water potential to lower water potential.

Important terms include turgor pressure, plasmolysis, apoplast, symplast, and Casparian strip. These ideas form the base for the whole chapter.

Most water enters through root hairs. Upward movement occurs through xylem as the ascent of sap. The most accepted explanation is the cohesion-tension-transpiration pull theory.

Root pressure can be seen in bleeding and guttation, but it cannot explain water rise to the top of tall trees.

Transpiration is the loss of water vapor from aerial parts, mainly through stomata. Guard cells regulate stomatal opening through turgor changes.

Light, temperature, humidity, and wind affect transpiration strongly. It helps in cooling and drives the xylem stream, which is why it is often called a necessary evil.

Food moves in plants mainly as sucrose through phloem. Mature leaves are usually sources, while growing regions, roots, fruits, and storage organs act as sinks.

The most accepted mechanism is the pressure-flow hypothesis, where loading at the source and unloading at the sink create the pressure gradient for mass flow.

Transport in plants becomes easy when seen as one linked system: membrane-level movement explains local uptake, xylem explains water and minerals, and phloem explains food translocation. The chapter is especially scoring when these are compared together.