Biology – 3.2 Osmosis | e-Consult

Osmosis is the net movement of water across a selectively permeable membrane from a region of high water potential (low solute concentration) to a region of low water potential (high solute concentration). The cell membrane is a selectively permeable barrier, meaning it allows some substances (like water) to pass through more easily than others (like large solute molecules). This selective permeability is crucial for osmosis.

Here's a description of what happens to a potato in different solutions:

1. Hypotonic Solution: A hypotonic solution has a higher water potential than the potato cells. Water moves into the potato cells by osmosis, causing them to swell. The cell membrane pushes against the cell wall, resulting in an increase in the potato's mass. If the pressure becomes too great, the cell may burst (lyse).
2. Isotonic Solution: An isotonic solution has the same water potential as the potato cells. There is no net movement of water. The potato cells maintain their normal shape and volume, and the potato's mass remains relatively constant.
3. Hypertonic Solution: A hypertonic solution has a lower water potential than the potato cells. Water moves out of the potato cells by osmosis, causing them to shrink. The cell membrane pulls away from the cell wall, resulting in a decrease in the potato's mass. This process is called plasmolysis.

Diagram (Conceptual - a real diagram would be included here):

A diagram would show three potatoes in separate beakers: one in a hypotonic solution, one in an isotonic solution, and one in a hypertonic solution. The hypotonic potato would be swollen, the isotonic potato would be normal, and the hypertonic potato would be shrunken.