Hypotonic, isotonic, and hypertonic solutions (tonicity) | Khan Academy

TL;DR

Water molecules will move across a semipermeable membrane, causing cell expansion or shrinkage depending on the concentration of solute in the solution.

Transcript

• [Voiceover] I have three different scenarios here of a cell being immersed in a solution, and the cell is this magenta circle, that's the cellular membrane. I have the water molecules depicted by these blue circles, and then, I have the solute inside of the solution, inside of the water solution that we depict with these yellow circles. I've clea... Read More

Key Insights

• 💦 The movement of water molecules across a semipermeable membrane is called osmosis.
• 💦 The concentration of solute in the solution determines the direction and net flow of water molecules.
• 🥺 A hypotonic solution leads to cell expansion, an isotonic solution has no net flow, and a hypertonic solution causes cell shrinkage.

Questions & Answers

Q: How does the size of water molecules and solute particles affect their movement across the membrane?

The water molecules and solute particles are depicted larger than the cell to visualize their movement. Water molecules have a higher probability of moving towards the membrane due to less obstruction from solute particles.

Q: How does the concentration of solute in the solution affect the movement of water molecules?

In a hypotonic solution, where solute concentration is lower outside the cell, water molecules move into the cell, resulting in cell expansion. In an isotonic solution, there is no net flow of water molecules. In a hypertonic solution, where solute concentration is higher outside the cell, water molecules move out of the cell, causing cell shrinkage.

Q: What happens to a cell in a hypotonic solution?

In a hypotonic solution, water molecules move into the cell, increasing the internal pressure. This can cause the cell to expand or even burst if the pressure becomes too high.

Q: How does osmosis affect red blood cells in different solutions?

In a hypotonic solution, red blood cells will swell and potentially rupture. In an isotonic solution, the red blood cells will maintain their normal shape. In a hypertonic solution, the red blood cells will shrink and become dehydrated.

Summary & Key Takeaways

• Water molecules can move across a semipermeable membrane from a hypotonic solution (lower solute concentration) to the inside of a cell, leading to cell expansion.

• In an isotonic solution (equal solute concentration), there is no net flow of water molecules.

• In a hypertonic solution (higher solute concentration), water molecules move from the inside of the cell to the outside, causing cell shrinkage.