This animation explains active transport across membranes and why it is needed! Transcript: Naturally, molecules and ions move from areas of high concentration to low concentration (down their concentration gradient). But what if you need them to move the other way, from low to high concentration (against their concentration gradient)? This requires energy and is called active transport. In active transport, ATP energy and transport proteins are used to pump particles against their concentration gradient, from low to high. Because this is going against the flow, it is like swimming upstream or pumping water uphill, and therefore requires energy to be used. It is easy to remember that active transport requires energy because doing active activities always uses energy. This is important anytime you need to concentrate a substance on one side of the membrane. In our sugar example, for instance, you might need to pull more sugar into the cell, even if the environment has a lower concentration. In this situation, your cell would use active transport. Remember, active transport uses ATP energy and transport proteins to pump particles from low to high! Credits: Music: www.bensound.com Photo by Alexander Schimmeck on Unsplash Photo by Kate Trysh on Unsplash Photo by Sebastian Staines on Unsplash Photo by Fabio Comparelli on Unsplash Photo by Brandon on Unsplash