Which body system work together to protect the body from pathogens?

Can bacteria reproduce in a way such that when you start out with two bacteria, you get five bacteria? why or why not? * a. yes, because bacteria reproduce sexually, and can produce any number of offspring, just as humans do. b. no, because bacteria grow at an exponential rate. c. no, because when bacteria reproduce, they split into two parts, and two bacteria splitting would result in four bacteria.

Several billion years ago which gas was the least prevailant in the atmosphere

Ascientific idea becomes valid when it is what?