Use the drop-down menus to complete the statements. ___are pure substances that cannot be broken down into a simpler form. are units of two or more atoms. ___ are the smallest possible particles of an element. ___are pure substances made of two or more atoms of different elements.

1) describe the physical layout of the ocean floor ? 2) explain how the dumbo octopus swims differently than other octopus species and why this would be an advantage in the aphonic zone . 3) why are the types of organisms that live at each underwater hot vent so dramatically different ?