a cell membrane is semi-permeable. meaning that it selectively chooses between what can go in and out of the cell. A door greeter is similar to this because a door greeter can tell who to allow in/out of the building they are in.
Cell membrane
Cell membrane
it controls what goes in and out of the cell like a door
I use to as a door greeter?
A door because the Cell Membrane controls what goes in and out of the cell, and so does a door. A door keeps things like wind and bugs out from coming inside, a door also saves you from losing cool air in the summer and heat in the winter.
It could be a gate. It is a gate because the door is the cell membrane. See you need to get past the cell wall before the cell membrane.
The cell membrane would be a locked door (for example) so that ONLY the people with a key can get in and the people without a key would not be able to get in.
It means that is/can be a door to a cell 'hence semi permeable membrane? (or to anything)
You could use lots of analogies. Cell membranes keep the traffic of things going on in the cell. It also keeps stuff in or out. You could say it works like screen a door. Perhaps a better analogy is that the cell membrane is like a border (between countries). The cell membrane (much like the border guards) control the traffic in and out of the cell. A fun answer could be to compare it to a Club bouncer, that allows certain people in and blocks the entrance of others. Another analogy for a cell membrane is that it is like a sieve. That is because it lets smaller particles (like water) in, while stopping bigger particles that could cause the cell harm out.
You could be referring to the cell membrane or carrier proteins. Both allow certain substances to enter cells.
An alternative to the cell wall is the cell membrane. While the cell wall provides structural support and protection in plant cells, the cell membrane controls the movement of materials in and out of the cell in both plant and animal cells.
Proteins in the cell membrane serve various functions such as transporting molecules in and out of the cell, acting as receptors for signaling molecules, and providing structural support for the membrane. They also help in cell-cell communication and adhesion, as well as in cell recognition and identification.