How do the circular folds in the small intestine allow more surface area for digestion

Environmental differences within ecosystems are generally caused by

The chemical form of energy that is useable by the cell to do work

Which scientific design has both practical limitations and limitations due to scale? studying the effect of bleach on the growth of mold spores exposing cultures of duckweed to different intensities of light observing the replication of dna molecules with a hand lens using colored marbles to model a cross between two colors of rabbits