Final answer:
The water potential of the cell is the sum of its solute and pressure potentials, which are -0.7 MPa and 0, respectively, resulting in a water potential of -0.7 MPa.
Step-by-step explanation:
The student's question about water potential involves understanding the concept of solute potential and pressure potential. In this case, the cell has a pressure potential (ψp) of 0 and a solute potential (ψs) of -0.7 MPa. To find the cell's water potential (ψw), which is the measure of the potential energy in water in a system compared to pure water, we use the equation ψw = ψs + ψp. Since the pressure potential is 0, the water potential is simply the sum of the solute potential and the pressure potential, which in this case is -0.7 MPa + 0 = -0.7 MPa. Therefore, the answer to the student's question is: A. -0.7 MPa.