In a cell if ΨP = + 0.3MPa and ΨS=-0.45MPa, then the resulting Ψ is ___. Enter your answer with either a + or a - before the number and no words.

The answer is Ψ = - 0.15 MPa.

The movement of water depends on the presence of solute, so it is referred as solute potential. But, as water enters the cells, it increases a pressure inside the cell, so this pressure is called pressure potential. The water potential (Ψ) is equal to the sum of pressure potential (ΨP) and solute potential (ΨS):

Ψ = ΨP + ΨS.

ΨP = + 0.3 MPa

ΨS = - 0.45 Mpa

Ψ = + 0.3 MPa + - 0.45MPa

Ψ = 0.3-0.45 MPa

Ψ = - 0.15 MPa