* Enclose a cell: A cell membrane is the outer boundary of a cell, separating the cell's internal environment from the external environment. So, anything that isn't a cell, like a rock, a piece of paper, or a cloud, would be a non-example.
* Have a phospholipid bilayer: The cell membrane is composed of a phospholipid bilayer, which is a double layer of phospholipid molecules. Anything that doesn't have this structure, like a plastic bag, a piece of fabric, or a metal sheet, would be a non-example.
* Be selectively permeable: The cell membrane is selectively permeable, meaning it allows some substances to pass through while blocking others. A non-example would be something that is not selective, like a sieve that lets everything through or a wall that blocks everything.
Here are some specific examples of non-examples:
* A wall: Walls are not selectively permeable and don't have a phospholipid bilayer.
* A plastic bag: Plastic bags don't have a phospholipid bilayer and aren't selectively permeable.
* A piece of paper: Paper is not a membrane, and it is not selectively permeable.
* A rock: Rocks are not cells and do not have cell membranes.
In essence, anything that isn't a thin, flexible, selectively permeable barrier surrounding a cell is a non-example of a cell membrane.
