Cells in the small intestine possess different sites for absorbing different types of amino acids, which causes competition among amino acids at the absorption sites. What is the reason for the competition among amino acids at the absorption sites in the small intestine?
1) Amino acids have different affinities for the absorption sites
2) Amino acids compete for limited space at the absorption sites
3) Amino acids inhibit each other's absorption
4) Amino acids are actively transported across the absorption sites