In roses assume that red or yellow flower color is controlled by a single gene with two alleles. When you cross roses with yellow flowers with each other you always get only roses that produce yellow flowers, but when you cross roses with red flowers with each other you sometimes get offspring that produce yellow flowers. If you take one of the rose plants with red flowers that sometimes produces offspring with yellow flowers and cross it with a rose plant that makes yellow flowers you would expect that their offspring will be:

the contamination

we are putting to many trash.

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.