Water potential - class-XII

Water potential is highest in pure water or wet soil (around 0 MPa or slightly negative) and decreases along the soil-plant-atmosphere continuum, reaching its lowest values in dry atmospheric air to drive transpiration.

Adding solute to a solution increases the solute concentration, which lowers its solute potential (makes it more negative) and consequently decreases the overall water potential of the solution.

After adding, solute in water its water potential decreases and solute potential increases.

Water potential (Psi_w) is correctly expressed as the sum of its components: matric potential (Psi_m), pressure potential (Psi_p), and solute potential (Psi_s), which corresponds to option C.

• The absorption of water by the solid particles of an adsorbent without forming a solution is called Imbibition.
  
• Imbibants have very high negative water potential. It is called the matric potential. Water has (the highest) maximum water potential (maximum being zero).
  

Pure water (i.e. water with no solutes) has a water potential value of 0. As you add solutes (i.e. sugar or salt) to water, the water potential value is lowered. This, therefore, means that the water potential value for any solution is always negative (as the value is lowered from the starting value of 0). Higher the concentration, lower is water potential.

The water potential of a plant cell is determined by the combined effects of solute concentration (solute potential) and turgor pressure (pressure potential).

Water potential (Psi_w) = Psi_s + Psi_p. For cell A: -20 + 8 = -12 bars. For cell B: -12 + 8 = -4 bars. Water moves from higher potential (-4) to lower potential (-12), so from B to A.

Water potential is the fundamental thermodynamic parameter that dictates the direction of water movement across membranes in biological systems.

Diffusion Pressure Deficit (DPD) is inversely related to water potential (DPD = -Psi_w for standard solutions without external pressure). Therefore, when the water potential of a cell increases, its DPD decreases.

The pressure potential is usually positive.

Statement I is correct because increasing solute potential (making it less negative or adding positive increments) increases water potential. Statement II is correct because pure water at standard temperature and pressure has a water potential defined as zero.

NaCl dissociates into two ions (Na+ and Cl-), while sucrose does not. Therefore, 1 M NaCl has a lower (more negative) solute potential than 1 M sucrose. Consequently, the water potential of the cell in sucrose solution will be greater.

The cell will swell when the concentration of solute is more inside the cell than the surrounding. Here the concentration of solute inside the cell is 0.4 M, and out of given solutions, 0.1 M solution has a lesser concentration of solute. So, the cell which is placed in a 0.1 M solution will swell. This phenomenon is called osmosis.

If a difference in water potential exists between the two regions, spontaneous movement of water will take place, provided the movement can occur between them. The direction of flow will be energetically down hill, that is from the region of higher water potential(root hair) to the region of lower water potential(xylem) via cortex from less negative water potential (e.g., - $1$ kPa) to more negative water potential (e.g., - $2$ kPa).

Pure water is with no dissolved solutes hence its potential is highest that is zero, as solute is added to water potential or energy of water becomes negative. Diffusion is movement of substances from their higher potential/energy/concentration to places of lower potential /energy/concentration hence does not require in put of energy.

DPD of cell A=5A=5 bars
DPD of cell B=5−5=0B=5−5=0 bars
DPD of cell C=10−4=6C=10−4=6 bars
DPD of cell D=8−3=5D=8−3=5 bars
As cell B has the lowest value of DPD, therefore water will move from cell B to cells A, C and D.

The phenomenon of breaking up of water into hydrogen and oxygen in the illuminated chloroplasts is called photolysis or photocatalytic splitting of water. It can be depicted as: $4H _{2} O \rightleftharpoons 4H^{+} + 4OH^{-}$
   $4OH^{-}\xrightarrow[Mn^{2} + ,Ca^{2} +, CI^{-}]{Oxygen ,, evolving ,, complex} 2H _{2}O + O _{2}\uparrow + 4e^- $

Water potential is the measure of the free energy of water which helps in the movement of water between any two systems. Water moves from the point where the water potential is greater to the point where the water potential is less. Addition of solutes decreases the water potential (becomes more negative). Temperature has no effect on water potential. The water potential of pure water is taken as zero. 

Water potential is generally most negative in mesophyll cell walls because water evaporates from the mesophyll cells into the air spaces in the leaf. If the air surrounding the leaf has less water vapor than the air in the intercellular spaces, water vapor will leave the leaf through stomata. Order of water to move through the plant from the soil to the air ( a process called transpiration).

• Water potential is the potential energy of water relative to pure water in a plant cell or tissue. This can be written as the sum of matrix potential (due to binding of water to cell and cytoplasm), the solute potential (due to concentration of dissolved solutes which by its effect on the entropy components reduces the water potential) and pressure potential (due to hydrostatic pressure, which by its effect on energy components increases the water potential).
  
• Ψw = Ψs + Ψp + Ψm
  
• So the correct answer is "All of these".
  

The liberation of $ O _{2}$ during photolysis of water involves the role of $ Mn^{2+},Ca^{2+}$ and $CI ^{-}$ ions.