Plant Absorption

Most plants absorb the water and nutrients they need from the soil through their roots.The soil solution can move freely into the root cortex via root hairs, however it cannot pass through the endodermis on its own due to the impenetrable Casparian strip.Cells in the endodermis actively transport necessary minerals into the vascular tissue and water follows because of osmosis.
Once in the vascular tissues, this nutrient and water solution must be transported throughout the plant so that it can be used to create food during photosynthesis.Xylem is the tissue responsible for transporting this solution up the stem to the leaves, while phloem is the tissue responsible for carrying sugary food molecule solution back down the stem to places where it is needed.
There is a problem in moving the solution upward against gravity that plants have to deal with.Root pressure pushes the solution upward because of the hydrostatic pressure that is created when water and ions move into the endodermis and cannot get back out.This is because the ions are actively transported and water follows them due to osmosis.Root pressure cannot provide enough of a push for the solution to reach the highest leaves, which is where the transpiration pull-water cohesion mechanism comes into play.This process relies upon transpiration, the evaporation of water from leaves, as well as the property of water called cohesion, or the sticking together of molecules of the same substance.Transpiration is controlled by the stomata, openings in the leaves that allow for gas exchange necessary for photosynthesis.When many stomata are open more transpiration will occur and when few stomata are open water is conserved.The mechanism works much like a domino effect.When water transpires through the outermost layer of leaf cells, a water molecule is borrowed or pulled from its neighboring cell, which continues all the way down the stem rapidly.This provides…

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