osmosis

osmosis

net movement of water molecules from a region of higher water potential to a region of lower water potential through a partially permeable membrane

• passive movement of water across a membrane

  • simple diffusion of water

  • bulk flow by facilitated diffusion (aquaporins)

water potential

measure of tendency of water molecules to enter/leave from one solution to another

types of solutions

water molecules move from a dilute solution to a more concentrated solution across a partially permeable membrane

hypertonic solution

solution which has a lower water potential than another

hypotonic solution

solution which has a higher water potential than another

isotonic solution

solution which has the same water potential as another

what happens to an animal cell in a solution with a higher water potential?

• When an animal cell is placed in a solution with a higher water potential, the cytoplasm has a lower water potential than the solution outside the cell.

• Water enters the cell by osmosis, causing it to swell and eventually burst due to the absence of a cell wall (cytolysis)

what happens to a plant cell in a solution with a higher water potential?

• When a plant cell is placed in a solution with a higher water potential, the cell sap has a lower water potential than the solution outside the cell.

• When water enters the cell by osmosis, the central vacuole increases in size. It pushes the cell contents against the cell wall.

• When the plant cell expands, it swells or becomes turgid (the cell is in a state of turgor). The pressure exerted by the water on the cell wall is called turgor pressure. The cell is prevented from bursting by the rigid and inelastic cell wall.

what happens to a plant cell in a solution with a lower water potential?

• When a plant cell is placed in a solution with a lower water potential, its cell sap has a higher water potential than the solution outside the cell.

• When water leaves the cell by osmosis, the vacuole shrinks and stops exerting pressure on the cell wall. The cell becomes flaccid.

• If the cell continues to lose water, the cell’s cell sap and cell membrane will shrink away from the cell wall. This process is known as plasmolysis.

• This can be reversed by placing the cell in a solution with a higher water potential than the cell sap.

what happens to an animal cell in a solution with a lower water potential?

• When an animal cell is placed in a solution with a lower water potential, its cytoplasm has a higher water potential than the solution outside the cell.

• When water leaves the cell by osmosis, the cell shrinks in size and becomes dehydrated

• As it shrinks, tiny spikes appear on the cell surface membranes. This process is called crenation.