Transport in Plants

Plant-water relations

  • Imbibition is the process of adsorption of water over a solid substance through capillary force of attraction.
  • Germination seeds imbibe water during its growth and that is responsible to break the seed coat and enlargement of solid wooden doors during the rainy season is due to imbibition.
  • Water potential (Ψω) is the reduction in the free energy of water when present in the cell (or) solution that is in its pure state. Ψw = Ψs + Ψp + Ψm.
  • Ψw of pure water is maximum and is considered to be zero; Ψw of the solution is always lesser than zero.
  • In Eqin 1. Ψm is disregarded as matric potential is insignificant in osmosis. Hence the equation changes to Ψw = Ψs + Ψp; Ψs is always negative for a solute-rich solution.
  • Osmosis is the movement of water molecules (solvent) from dilute region to concentrated region through a semi-permeable membrane that could be explained by potato – osmoscope and thistle funnel experiment.
  • Osmosis is of 2 type (i) Exosmosis (movement of water from the cell to outside) (ii) Endosmosis (movement of water inside the cell).
  • Osmotic pressure (o.p) π is the pressure exerted to stop the osmosis process. O.P = mRT---->eqn.2, where
           m – molar concentration
           R – gas constant
           T – Temperature
  • For an electrolytic system, eqn.2 Changes as O.P = mRT × I. Where I – Ionization potential.
  • 1 M NaCl has higher O.P than 1m glucose.
  • Electrolytes and Halophytes have higher O.P than non-electrolytes and Hydrophytes respectively.
  • A solution whose concentration is greater than the other solution is called hypertonic solution. The latter solution is called Hypotonic solution. An isotonic solution has a similar concentration range.
  • Shrinkage of the protoplast of a cell from its cell wall, when it is placed in a hypertonic solution is called plasmolysis and is of 3 stages.
                  (i) Limiting plasmolysis,
                  (ii) Incipient plasmolysis , and
                  (iii) Evident plasmolysis
  • DPD [diffusion Pressure deficit] = O.P – T.P, when
          O.P – Osmotic pressure
          T.P – Turgor pressure.
  • When a cell is placed in a hypertonic solution the cell wall exerts a pressure against the protoplasm, called wall pressure. An equal but opposite pressure exerted towards the wall from protoplasm is called turgor pressure. So, [T.P = −W.P]
  • D.P.D is also termed as the suction pressure
  • Water moves from a cell of low DPD to a high DPD.
  • Water moves from a cell of high Ψw to low Ψw
  • Hence [ D.P.D = − Ψw]

View this video for the topic from 31:47 to 53:11

Disclaimer: may from time to time provide links to third party Internet sites under their respective fair use policy and it may from time to time provide materials from such third parties on this website. These third party sites and any third party materials are provided for viewers convenience and for non-commercial educational purpose only. Compete does not operate or control in any respect any information, products or services available on these third party sites. makes no representations whatsoever concerning the content of these sites and the fact that has provided a link to such sites is NOT an endorsement, authorization, sponsorship, or affiliation by with respect to such sites, its services, the products displayed, its owners, or its providers.