pH, buffer and cell constituents

Lesson 3 : Water, pH and Buffers

pH, buffer and cell constituents

Water is the major constituent of most plant cells, but the amount varies with cell type and physiological condition.

  1. carrot root is about 85% water
  2. young lettuce leaves can contain 95% water
  3. dry seed may be only 5% water (usually around 10 to 15%)

Ionization of Water and pH: Some of the water molecules separate into [H+] and [OH-] ions. The tendency of these ions to recombine is a function of the chances for collisions between them, which depends on the number of ions in solution. This is the mass law relationship and may be expressed mathematically by saying that the product of the molar concentrations equals a constant: [H+]*[OH-] = K. This constant, K, is equal to 10-14 with the reaction, H+ + OH- --> H2O, proceeding in such a way as to assure this constancy. So in pure water both [H+] and [OH-] = 10-7 molar (M). However, water is seldom pure enough to contain equal numbers of hydrogen and hydroxyl ions. There are almost always some ions dissolved in water and the amount of cations and anions in solution determine the ratio of H+ and OH- and, thus, the pH of the solution

Imbibition (imbibe = to drink)
During imbibition, H20 enters by diffusion (even occurs in dead seed)


Functions of imbibition

  • enzyme hydration
  • metabolite mobilization
  • development of turgor pressure for cell expansion

Growth occurs after imbibition

  • H20 enters by osmosis
  • new enzymes are made
  • new cell wall materials are produced
  • respiration parallels growth
Last modified: Tuesday, 17 January 2012, 5:42 AM