Answer to Question #62485 in Biochemistry for Marisa McGonigal

Question

Chemical fertilizers are composed of salts that that dissolve into soil moisture and then are absorbed by the root cells of the plants. Why should you never over fertilize a plant?

Answer 1

When you over-fertilize a plant, you're putting a lot of excess solutes (soluble stuff) outside of the roots in the soil. Fertilizer may form a hypertonic solution in the soil that may draw out the water from the plant cells causing the plant to die.
In a hypertonic solution, the total molar concentration of all dissolved solute particles is greater than that of another solution, or greater than the concentration in a cell.
If concentrations of dissolved solutes are greater outside the cell, the concentration of water outside is correspondingly lower. As a result, water inside the cell will flow outwards to attain equilibrium, causing the cell to shrink. As cells lose water, they lose the ability to function.