Researchers investigate the transport of a certain protein into the cells by endocytosis. In an experiment, the researchers incubate the cells in the presence of the protein and measure the amount of the protein that is absorbed into the cells over a five minute period. Based on their observations, what should the researchers do to further clarify how the availability of the protein outside the cells affects the rate of endocytosis of the protein?

The study aims to determine whether the availability of the protein outside the cells affects the rate of endocytosis. If the researchers would like to determine if the availability of protein has an effect on the rate, they should test it by varying the amount of protein they incubate the cells in.They can do this by incubating the cells with less or more proteins. If the rate of endocytosis would vary in each accordingly then they could better verify their claim.

It is important though that they keep everything else constant to prevent invalid results.This would mean that they need to keep the time period the same, including the type of cells. (this would be the controlled variables)