Transport in Plants
- 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
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