CELLS need to be able to move SUBSTANCES both in and out. There are different ways they can do this. Some of these happen automatically - this is called PASSIVE TRANSPORT because it happens by itself, across a CONCENTRATION GRADIENT, and so the cell does NOT need to use energy for it.

However, sometimes it needs to move important substances in or out of the cell and there is no difference in concentration for it to happen automatically..... SO to make it happen the cell NEEDS TO USE ENERGY. This is called ACTIVE TRANSPORT.

This is a very simple video which explains exactly WHICH SUBSTANCES (e.g. oxygen, glucose, etc) are moved by PASSIVE TRANSPORT and WHICH SUBSTANCES are moved by ACTIVE TRANSPORT and it also tells you WHY!