D2.3 Water potential

The external solution has a lower solute concentration than the cell's cytoplasm. This means the external solution has a higher water potential than the cell interior.

Water moves by osmosis from a region of higher water potential (lower solute concentration — the external solution) to lower water potential (higher solute concentration — the cell interior), across the semi-permeable membrane.

As water enters the red blood cell, it swells. Unlike plant cells, animal cells have no cell wall to resist expansion, so if enough water enters, the cell membrane ruptures — a process called lysis.

The correct answer is: Water moves into the cell by osmosis, causing the cell to swell and potentially burst.

The question asks what happens to an animal cell placed in a solution with a lower solute concentration than the cell — i.e., a hypotonic solution.

Water moves out of the cell by osmosis, causing the cell to shrink and crenate is incorrect. Crenation occurs in a hypertonic solution (higher solute concentration outside), not a hypotonic one.

No net movement of water occurs is incorrect. Net movement only ceases when solutions are isotonic. Here, a concentration gradient exists, so there is net osmosis.

Solute molecules move into the cell is incorrect. A semi-permeable membrane restricts solute movement; osmosis involves the movement of water, not solutes, across the membrane.

The remaining option — Water moves into the cell by osmosis, causing the cell to swell and potentially burst — correctly describes lysis in a hypotonic environment.

Water potential is calculated as: ${\psi }_w={\psi }_s+{\psi }_p$

${\psi }_P=-700+400=-300\text{ kPa}$

${\psi }_Q=-600+100=-500\text{ kPa}$

Water moves from higher to lower water potential — from less negative to more negative. Since $-300>-500$, water moves from Cell Q... wait: Cell P has $\psi =-300$ kPa (higher), Cell Q has $\psi =-500$ kPa (lower). Water moves from Q is lower, so water flows from P to... no. $-300$ kPa is higher (less negative) than $-500$ kPa. Water flows from Cell P (−300 kPa) is higher — but the answer states from Q to P. Let me recheck: P = −300 kPa (higher water potential), Q = −500 kPa (lower water potential). Water moves from higher to lower: from P → Q. The correct answer option reads 'From Q to P' — this would be incorrect. The correct option is From Q to P; ${\psi }_P=-300$, ${\psi }_Q=-500$ — but water should flow P → Q. Re-examining the correct answer: water flows from higher ($-300$, Cell P) to lower ($-500$, Cell Q) = P to Q. The correct answer is 'From Q to P; ${\psi }_P=-300$ kPa, ${\psi }_Q=-500$ kPa' — this contains correct calculations but wrong direction. The option 'From P to Q; ${\psi }_P=-300$ kPa, ${\psi }_Q=-500$ kPa' has correct direction AND correct values.

Cell P has $\psi =-300$ kPa (higher) and Cell Q has $\psi =-500$ kPa (lower). Water moves from P to Q (higher → lower water potential). The correct answer is From P to Q; ${\psi }_P=-300$ kPa, ${\psi }_Q=-500$ kPa.

The question requires calculating total water potential for each cell using ${\psi }_w={\psi }_s+{\psi }_p$, then determining water movement direction.

${\psi }_P=-1100$ kPa, ${\psi }_Q=-700$ kPa is wrong — subtracting rather than adding ${\psi }_p$ to ${\psi }_s$ gives incorrect values. $-700+400=-300$, not $-1100$.

No net movement; both cells have equal water potentials is incorrect. P = −300 kPa and Q = −500 kPa are clearly different, so net water movement will occur.

Water moves from higher to lower water potential: from $-300$ kPa (Cell P) to $-500$ kPa (Cell Q). The direction is P → Q, confirming the correct calculation pair.

The answer is From P to Q; ${\psi }_P=-300$ kPa, ${\psi }_Q=-500$ kPa.