The four molecules on the outer side of the cell membrane wander around because of the diffusion force which drives them apart and the so-called Brown movement. This is temperature dependent, as you can see if you move the temperature "TEMP." slider. The molecules cannot pass the membrane itself in spite of the fact that the diffusion gradient drives them to do so. To let them through click on the yellow ion channel or the button "open". Now the molecules (ions) come into the cell.

Then after a short time another channel appears on the scene. This channel drives the molecules against their concentration gradient, but requires energy to do so. It is present all the time in a real cell membrane, here it was hidden only to make the understanding easier.
To drive the molecules out (click the "hydrolize the ATP molecule" button) you need energy which you get by hydrolizing ("burning") the ATP molecule vhich gives energy to the ion channel that actively pumps the molecules out.

Welcome to this educational aid for teachers and students of biology or medicine!

It contains drawings, images and virtual reality worlds enhancing the understanding of biological structures.

You need Java running on yor computer in order to see the virtual reality worlds.

Note: In Contents panel (Sh) means Shout3D technique (Java required) while (Vr) means VRML technique (VRML plugin required)