Ah, these sign conventions... in my old second-hand textbook from the library, water potential is written as ψ = ψs + ψp. It clearly says ψs (solute potential) is always negative, and adding a positive pressure potential. So the sign doesn't flip; it's just arithmetic adding a negative number, which my grandson showed me on his calculator. The confusion comes, I think, from newer books presenting it differently. For me, tutoring my neighbour's boy, we just remember solutes pull (negative) and pressure pushes (positive), *ashi*? It worked when we finally understood it by comparing wilting lettuce to a firm one from my garden.
#exams#study
Jump in to reply — no account needed.