The answer to your question would be space. The sun's light travles through space. but if you clap, you can't hear it.
Endocytosis and exocytosis are similar in that they are both forms of cell transport. They differ because in endocytosis, a cell transports molecules into a cell (think: endo - in), and in exocytosis, the cell's molecules are transported by being expelled.
Answer:
species richness is the number of species in an ecosystem
