Advances in the study of what led to a classification system based on evolutionary relationships.

All phases of matter may have a fixed mass

What are the three different shapes, or structures, of carbon-based molecules

1. in what ways have non-native species been beneficial? 2. what are some of the hypotheses for the collapse of honeybee colonies? 3. distinguish between regional and functional extinction. 4. why is it difficult to measure background extinction rates? 5. what three factors are most important in causing extinction rates to climb?