Assume that the import of a particular amino acid across the plasma membrane is observed (1) to occur only down its concentration gradient and (2) to slow when a different but similar amino acid is added to the extracellular fluid. The movement of the amino acid through the membrane is most likely by:

They must use the scientific method

1) the mayans built pyramids just like the egyptians. the mayans also used hieroglyphics like them.2) power was passed down by family. for example, if the father dies, the son would be the next king.3)they both built pyramids for their structures.4)the main crop for the mayans was maize.5)they also grew manioc, beans,  squash,  amaranth, and chile peppers.

It's either -limiting factors or -scarce resources but i'd go with my first answer since the food and water are abundant they really aren't scarce