An equator, is the definition of that!
Cell Membrane = Controls what comes into and out of a cell; found in plant and animal cells
Observation– the process of using the five senses to gather information.
Trees can be made again . Water is a natural resource fuel is too . Wind
The atria of the heart merely need to allow blood to flow into the ventricle, and therefore aren't very muscular.
The ventricles of the heart need to actually pump blood to the rest of the body, whether to the lungs or the the rest of the body.