Which physical property of a medium is defined by how close the particles of the substance are to each other?

One group of reptiles, characterized by the fossil ark metal x

Match the digestive enzymes to the macro molecules they to digest. down fats into glycerol and fatty acids down carbohydrates into simple sugars down nucleic acids into nitrogenous bases and simple sugars down proteins into amino acids

What are the doorways into and out of cells, attached to the membrane, and built in the rough er.