Question

If the osmotic potential of a cell is –10 bars and its pressure potential is 5 bars. Its water potential would be:
A. -5 bars
B. 5 bars
C. -10 bars
D. 10 bars

Answer 1

Hint: Water potential of a solution is the algebraic sum of osmotic potential, pressure potential, and matrix potential.

Complete answer: The water potential of a solution is the algebraic sum of osmotic potential, pressure potential, and matrix potential.
Osmotic potential is the potential of water molecules to move from a hypotonic solution to a hypertonic solution across a semi-permeable membrane. It has a negative value as an increase in osmotic potential results in the exit of water from the cell.
Pressure potential is the hydrostatic pressure that is exerted on the water in a cell. In turgid plant cells, it usually has a positive value as the entry of water causes the protoplast to push against the cell wall.
Matrix potential constitutes the adhesive intermolecular forces between the water and the solid when they are in contact with them.

Additional information: An increase in turgor pressure results in the swelling of cells and eventually bursting. Loss of turgor pressure results in loos of fluids, ex: wilting of leaves. The cell wall and plasma membrane are responsible for the turgor pressure.
The water potential of pure water is zero.

Hence, the water potential will be = (-10+5) = -5 bars

Note: Osmotic pressure is due to the different concentrations of solutes across a membrane.
When a compartment (A) has more solute compared to the other compartment (B), the water/ solvent moves from the compartment (B) to (A).
Similar pressures known as the root pressure cause the absorption of water and minerals from the soil and transport it to the leaves for photosynthesis.
Imbibition is another plant-based pressure that causes the seed to open while germinating. Here the moisture from the surrounding is absorbed through the hilum to build up pressure to break the shell.
A bar is a unit of pressure, I bar equals 100000 pascals.