"Isotonic to the environment" means that the concentration of solutes inside a cell is the same as the concentration of solutes outside the cell. In simpler terms, the cell and its surroundings have the same "saltiness".

Here's why this is important:

* Water movement: Water moves across cell membranes to try and balance the concentration of solutes.

* If the environment is hypertonic (more concentrated than the cell), water will move out of the cell, causing it to shrink.

* If the environment is hypotonic (less concentrated than the cell), water will move into the cell, causing it to swell.

* Cell function: Cells need a stable environment to function properly. If the environment is not isotonic, it can disrupt the cell's processes and potentially damage it.

Examples:

* Red blood cells: Red blood cells need to be in an isotonic environment to function properly. If they are placed in a hypotonic solution, they will swell and burst. If they are placed in a hypertonic solution, they will shrink and become crenated.

* Plants: Plant cells have a cell wall that helps them maintain their shape. However, if the environment is too hypotonic, the cell wall can be stretched too much, leading to damage.

In summary: Being "isotonic to the environment" ensures that there is no net movement of water across the cell membrane, maintaining the cell's size and allowing it to function normally.