The first known single-celled organisms appeared on Earth about 3.5 billion years ago, roughly a billion years after Earth formed. More complex forms of life took longer to evolve, with the first multicellular animals not appearing until about 600 million years ago.
Large organisms include...
Mammals (Mammalia)
Stem-mammals (Synapsida)
Reptiles (Reptilia)
Dinosaurs (Dinosauria)
B. The nervous system collects and responds to information about the external and internal environment.
<span>It is the variable in an experiment is not directly altered</span>
Cholera develops when the bacterial toxin prevents G-protein inactivation , which leads to the continuous production of cAMP.
