Samples of blood were mixed with different sodium chloride solutions. In one concentration of sodium chloride, the red blood cells were observed to maintain their normal shape. In another concentration of sodium chloride, the red blood cells were observed to swell and burst. The cells which maintained their normal shape were in a state of homeostasis.

b tumor cells have a cell wall instead of a membrane

explanation:

tumor cells different from normal cells because tumor cells have a cell wall instead of a membrane.

it provides an alternative energy pathway for the reaction to proceed.

a catalyst is a substance that speeds up the rate of a chemical reaction but is not consumed during the course of the reaction.

catalysts increase the rate of reaction without being used up. they do this by lowering the activation energy needed. with a catalyst, more collisions result in a reaction, so the rate of reaction increases. different reactions need different catalysts.

a catalyst works by providing an alternative reaction pathway to the reaction product. the rate of the reaction is increased as this alternative route has a lower activation energy than the reaction route not mediated by the catalyst.

yes, because even though a theory has a  lot of evidence to support it, it is not always true