Which two processes are responsible for keeping the percentage of atmospheric oxygen at relatively constant levels

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

The asian shore crab (hemigrapsus sanguineus) is an invasive species that has impacted the atlantic coast. predict what characteristic of this invader would most likely disrupt the biodiversity of this area.

Variety of living organisms; includes genetic, species, and ecological types.