Which is true about ecosystems? a. once defined, an ecosystem is a unit scientists can analyze. b. all ecosystems are the same size. c. biotic and abiotic factors are the same in most ecosystems. d. all ecosystems are identical.

Which group of chordates does  notpossess true backbones?                 a.  birds      b.  frogs and toads      c.  lampreys      d.  crocodilians

19. scientists use meteorites that hit earth to provide evidence of the composition of earth's interior because they hypothesize that

The earth consists of a variety of different organisms. despite their diversity, however, some similarities on the structural and metabolic levels may be seen. these similarities can be attributed to a. similarities among organisms in their proteins and nucleic acids. b. the ability of organisms to readily adapt to sudden environmental changes. c. similarities in organisms' habitats and niches. d. the ability of all organisms to interbreed and produce new species.