You are studying the transport of a particular substance into epithelial cells grown in culture. you notice that you can only find the substance inside the cell when atp is present. how is the protein moving through the membrane?

Active transport

Explanation:

This protein is moving across the membrane through active transport.

In this type of transport the substances are transported with energy expenditure, ie in the presence of ATP, as is happening with the protein transport shown in the question above. Active transport may occur from the lowest to the highest concentration.

Active transport acts as a “revolving door”. The molecule to be transported binds to the carrier molecule (membrane protein) as an enzyme binds to the substrate. The carrier molecule spins and releases the charged molecule on the other side of the membrane.