Why don't ecosystems systems exist between fresh and salt water systems?

Explain the side effects of cancer treatments

The distant ancestors of tigers may have had bodies without stripes. use the theory of natural selection to explain how tigers may have evolved to have stripes.

The scales shown in the introduction measure mass, or the amount of matter in a particular object. the scientific law of conservation of mass states that matter cannot be created or destroyed during a chemical reaction, but it can change from one form to another. did the simulation support this scientific law? explain why or why not.