Two terms, one equation, and a sign convention that decides more marks than anything else in the unit.
Tonicity is a comparison, never a property. A solution is only hypertonic relative to something else — and the same solution can be hypotonic to one cell and hypertonic to another.
Hypertonic means more solute than the other side. Used on its own the word means nothing.
More solute means lower water potential, and water moves down that gradient — every time.
A cellulose wall lets pressure build until uptake stops. Animal cells have no such brake, so they burst.
Tap each part. The two terms of the equation are both visible here — one in the vacuole, one at the wall.
Tap the cell wall, the plasma membrane, the cytoplasm, the vacuole, the turgor arrows or the equation panel.
Move the sliders and watch both water potentials change. The arrow always points from higher to lower — that is the only rule you need.
The same cell in three solutions. Watch what happens to the pressure term.
Almost every lost mark in this topic is a sign error. Solute potential is negative. Pressure potential is positive. Pure water is zero, and nothing is ever above it.
i is the number of particles per formula unit: 1 for sucrose, 2 for NaCl. Always negative.
Zero in an open beaker and in a flaccid cell. Positive in a turgid one, because the wall pushes back.
Water moves from higher Ψ to lower Ψ. −3 is higher than −7, and that catches people out constantly.
Water crosses freely in both directions; the solute cannot cross at all. Nothing here is being pushed.
Tap a node to light up its connections. The pink dashed link is the one that unlocks the calculation questions.
Two terms, one gradient, and a wall that changes everything for plants.
Drag a term into a gap, or tap a term and then tap a gap. Two terms belong nowhere.
Water moves down a gradient, from the less negative side to the more negative one. A cell placed in a solution gains water, while one placed in a solution loses it. A plant cell that has gained water becomes , whereas one that has lost enough water undergoes . The wall pushing back on the protoplast is the , which is positive. In an open beaker that term is , and adding solute always makes the solute potential more .
Two of these are calculations. Single best answer, with the reasoning as soon as you commit.